From a476f73f6c8a983266d02d334a8fb8233316680d Mon Sep 17 00:00:00 2001
From: Tom Arn <sw@t-arn.com>
Date: Tue, 13 May 2025 07:34:22 +0200
Subject: [PATCH 01/27] * implented on_navigation_started for winforms *
 implented on_navigation_started for android * extended the webview example

---
 android/src/toga_android/widgets/webview.py   | 34 +++++++++++++++++--
 cocoa/src/toga_cocoa/widgets/webview.py       |  2 ++
 core/src/toga/widgets/webview.py              | 26 ++++++++++++++
 examples/webview/webview/app.py               | 16 +++++++++
 gtk/src/toga_gtk/widgets/webview.py           |  1 +
 iOS/src/toga_iOS/widgets/webview.py           |  2 ++
 winforms/src/toga_winforms/widgets/webview.py | 12 +++++++
 7 files changed, 91 insertions(+), 2 deletions(-)

diff --git a/android/src/toga_android/widgets/webview.py b/android/src/toga_android/widgets/webview.py
index 7699e8f56f..5b431c05cd 100644
--- a/android/src/toga_android/widgets/webview.py
+++ b/android/src/toga_android/widgets/webview.py
@@ -2,7 +2,7 @@
 from http.cookiejar import CookieJar
 
 from android.webkit import ValueCallback, WebView as A_WebView, WebViewClient
-from java import dynamic_proxy
+from java import dynamic_proxy, static_proxy, constructor, jboolean, jclass, Override
 
 from toga.widgets.webview import CookiesResult, JavaScriptResult
 
@@ -23,6 +23,31 @@ def onReceiveValue(self, value):
         self.result.set_result(res)
 
 
+class TogaNavigationEvent():
+    def __init__(self, webresourcerequest):
+        self.request = webresourcerequest
+        self.cancel = False
+
+
+class TogaWebClient(static_proxy(WebViewClient)):
+    def __init__(self, impl):
+        super().__init__()
+        self.webview_impl = impl
+
+    @Override(jboolean, [A_WebView, WebResourceRequest])
+    def shouldOverrideUrlLoading(self, webview, webresourcerequest):
+        if self.webview_impl.interface.on_navigation_starting:
+            event = TogaNavigationEvent(webresourcerequest)
+            allow = self.webview_impl.interface.on_navigation_starting(
+                webresourcerequest.getUrl().toString()
+            )
+            if not allow:
+                event.cancel = True
+                event = None
+                return True
+        return False
+
+
 class WebView(Widget):
     SUPPORTS_ON_WEBVIEW_LOAD = False
 
@@ -30,7 +55,8 @@ def create(self):
         self.native = A_WebView(self._native_activity)
         # Set a WebViewClient so that new links open in this activity,
         # rather than triggering the phone's web browser.
-        self.native.setWebViewClient(WebViewClient())
+        client = TogaWebClient(self)
+        self.native.setWebViewClient(client)
 
         self.settings = self.native.getSettings()
         self.default_user_agent = self.settings.getUserAgentString()
@@ -86,3 +112,7 @@ def evaluate_javascript(self, javascript, on_result=None):
 
         self.native.evaluateJavascript(javascript, ReceiveString(result))
         return result
+
+    def set_on_navigation_starting(self, handler):
+        # print(f"set_on_navigation_starting")
+        pass
\ No newline at end of file
diff --git a/cocoa/src/toga_cocoa/widgets/webview.py b/cocoa/src/toga_cocoa/widgets/webview.py
index c7b79835a0..9db5d850fe 100644
--- a/cocoa/src/toga_cocoa/widgets/webview.py
+++ b/cocoa/src/toga_cocoa/widgets/webview.py
@@ -80,6 +80,8 @@ def acceptsFirstResponder(self) -> bool:
 
 
 class WebView(Widget):
+    SUPPORTS_ON_NAVIGATION_STARTING = False
+
     def create(self):
         self.native = TogaWebView.alloc().init()
         self.native.interface = self.interface
diff --git a/core/src/toga/widgets/webview.py b/core/src/toga/widgets/webview.py
index 8fc79c7d09..868463be79 100644
--- a/core/src/toga/widgets/webview.py
+++ b/core/src/toga/widgets/webview.py
@@ -33,6 +33,7 @@ def __init__(
         url: str | None = None,
         content: str | None = None,
         user_agent: str | None = None,
+        on_navigation_starting = None,
         on_webview_load: OnWebViewLoadHandler | None = None,
         **kwargs,
     ):
@@ -50,6 +51,9 @@ def __init__(
             value provided for the ``url`` argument will be ignored.
         :param user_agent: The user agent to use for web requests. If not
             provided, the default user agent for the platform will be used.
+        :param on_navigation_starting: A handler that will be invoked when the 
+            web view is requesting permission to navigate or redirect 
+            to a different URI. 
         :param on_webview_load: A handler that will be invoked when the web view
             finishes loading.
         :param kwargs: Initial style properties.
@@ -60,6 +64,7 @@ def __init__(
 
         # Set the load handler before loading the first URL.
         self.on_webview_load = on_webview_load
+        self.on_navigation_starting = on_navigation_starting
 
         # Load both content and root URL if it's provided by the user.
         # Otherwise, load the URL only.
@@ -104,6 +109,27 @@ async def load_url(self, url: str) -> asyncio.Future:
         self._set_url(url, future=loaded_future)
         return await loaded_future
 
+    @property
+    def on_navigation_starting(self):
+        """A handler that will be invoked when the webview is requesting 
+        permission to navigate or redirect to a different URI.
+        
+        The handler will receive the arguments `widget` and `url` and must 
+        return True to allow the navigation or False to deny the navigation to the URL.
+
+        :returns: The function ``callable`` that is called by this navigation event.
+        """
+        return self._on_navigation_starting
+
+    @on_navigation_starting.setter
+    def on_navigation_starting(self, handler):
+        """Set the handler to invoke when the webview starts navigating """
+        if handler and not getattr(self._impl, "SUPPORTS_ON_NAVIGATION_STARTING", True):
+            self.factory.not_implemented("WebView.on_navigation_starting")
+        
+        self._on_navigation_starting = wrapped_handler(self, handler)
+        self._impl.set_on_navigation_starting(self._on_navigation_starting)
+
     @property
     def on_webview_load(self) -> OnWebViewLoadHandler:
         """The handler to invoke when the web view finishes loading.
diff --git a/examples/webview/webview/app.py b/examples/webview/webview/app.py
index 46fc8066db..8a9ba98eae 100644
--- a/examples/webview/webview/app.py
+++ b/examples/webview/webview/app.py
@@ -1,9 +1,12 @@
 import toga
 from toga.constants import COLUMN, ROW
 from toga.style import Pack
+import asyncio
 
 
 class ExampleWebView(toga.App):
+    allowed_base_url = "https://beeware.org/"
+
     async def on_do_async_js(self, widget, **kwargs):
         self.label.text = repr(await self.webview.evaluate_javascript("2 + 2"))
 
@@ -22,6 +25,16 @@ def on_bad_js_result(self, result, *, exception=None):
     def on_webview_load(self, widget, **kwargs):
         self.label.text = "www loaded!"
 
+    def on_navigation_starting(self, widget, url):
+        # print(f"on_navigation_starting: {url}")
+        allow = True
+        if !url.startswith(allowed_base_url):
+            allow = False
+            message = f"Navigation not allowed to: {url}"
+            dialog = toga.InfoDialog("on_navigation_starting()", message)
+            task = asyncio.create_task(self.dialog(dialog))
+        return allow
+            
     def on_set_url(self, widget, **kwargs):
         self.label.text = "Loading page..."
         self.webview.url = "https://beeware.org/"
@@ -92,6 +105,9 @@ def startup(self):
             on_webview_load=self.on_webview_load,
             style=Pack(flex=1),
         )
+        # activate web navigation filtering on supported platforms
+        if getattr(self.webview._impl, "SUPPORTS_ON_NAVIGATION_STARTING", True):
+            self.webview.on_navigation_starting = self.on_navigation_starting
 
         box = toga.Box(
             children=[
diff --git a/gtk/src/toga_gtk/widgets/webview.py b/gtk/src/toga_gtk/widgets/webview.py
index 6e135795d5..ea548e8a35 100644
--- a/gtk/src/toga_gtk/widgets/webview.py
+++ b/gtk/src/toga_gtk/widgets/webview.py
@@ -10,6 +10,7 @@
 
 class WebView(Widget):
     """GTK WebView implementation."""
+    SUPPORTS_ON_NAVIGATION_STARTING = False
 
     def create(self):
         if GTK_VERSION >= (4, 0, 0):  # pragma: no-cover-if-gtk3
diff --git a/iOS/src/toga_iOS/widgets/webview.py b/iOS/src/toga_iOS/widgets/webview.py
index f89f00dcd5..0f683998e8 100644
--- a/iOS/src/toga_iOS/widgets/webview.py
+++ b/iOS/src/toga_iOS/widgets/webview.py
@@ -76,6 +76,8 @@ def webView_didFinishNavigation_(self, navigation) -> None:
 
 
 class WebView(Widget):
+    SUPPORTS_ON_NAVIGATION_STARTING = False
+
     def create(self):
         self.native = TogaWebView.alloc().init()
         self.native.interface = self.interface
diff --git a/winforms/src/toga_winforms/widgets/webview.py b/winforms/src/toga_winforms/widgets/webview.py
index 71d71698d2..bbf4313f22 100644
--- a/winforms/src/toga_winforms/widgets/webview.py
+++ b/winforms/src/toga_winforms/widgets/webview.py
@@ -136,6 +136,8 @@ def winforms_initialization_completed(self, sender, args):
             settings.IsSwipeNavigationEnabled = False
             settings.IsZoomControlEnabled = True
 
+            self.native.CoreWebView2.NavigationStarting += self.winforms_navigation_starting
+            
             for task in self.pending_tasks:
                 task()
             self.pending_tasks = None
@@ -179,6 +181,13 @@ def winforms_navigation_completed(self, sender, args):
             self.loaded_future.set_result(None)
             self.loaded_future = None
 
+    def winforms_navigation_starting(self, sender, event):
+        print(f"winforms_navigation_starting: {event.Uri}")
+        if self.interface.on_navigation_starting:
+            allow = self.interface.on_navigation_starting(event.Uri)
+            if not allow:
+                event.Cancel = True
+
     def get_url(self):
         source = self.native.Source
         if source is None:  # pragma: nocover
@@ -234,6 +243,9 @@ def get_cookies(self):
 
         return result
 
+    def set_on_navigation_starting(self, handler):
+        pass
+
     def evaluate_javascript(self, javascript, on_result=None):
         result = JavaScriptResult(on_result)
         task_scheduler = TaskScheduler.FromCurrentSynchronizationContext()

From 23e2747dd044d380763ac57b384d327ed2b1bd7a Mon Sep 17 00:00:00 2001
From: Tom Arn <sw@t-arn.com>
Date: Tue, 13 May 2025 13:31:57 +0200
Subject: [PATCH 02/27] * fixed some issues

---
 android/src/toga_android/widgets/webview.py   | 13 +++++++++----
 examples/webview/pyproject.toml               |  4 ++++
 examples/webview/webview/app.py               | 13 +++++++------
 winforms/src/toga_winforms/widgets/webview.py |  8 +++++---
 4 files changed, 25 insertions(+), 13 deletions(-)

diff --git a/android/src/toga_android/widgets/webview.py b/android/src/toga_android/widgets/webview.py
index 5b431c05cd..19f711b77c 100644
--- a/android/src/toga_android/widgets/webview.py
+++ b/android/src/toga_android/widgets/webview.py
@@ -1,8 +1,13 @@
 import json
 from http.cookiejar import CookieJar
 
-from android.webkit import ValueCallback, WebView as A_WebView, WebViewClient
-from java import dynamic_proxy, static_proxy, constructor, jboolean, jclass, Override
+from android.webkit import (
+    ValueCallback,
+    WebResourceRequest,
+    WebView as A_WebView,
+    WebViewClient,
+)
+from java import Override, dynamic_proxy, jboolean, static_proxy
 
 from toga.widgets.webview import CookiesResult, JavaScriptResult
 
@@ -23,7 +28,7 @@ def onReceiveValue(self, value):
         self.result.set_result(res)
 
 
-class TogaNavigationEvent():
+class TogaNavigationEvent:
     def __init__(self, webresourcerequest):
         self.request = webresourcerequest
         self.cancel = False
@@ -115,4 +120,4 @@ def evaluate_javascript(self, javascript, on_result=None):
 
     def set_on_navigation_starting(self, handler):
         # print(f"set_on_navigation_starting")
-        pass
\ No newline at end of file
+        pass
diff --git a/examples/webview/pyproject.toml b/examples/webview/pyproject.toml
index 70c7994eb6..edfb984bb5 100644
--- a/examples/webview/pyproject.toml
+++ b/examples/webview/pyproject.toml
@@ -53,6 +53,10 @@ build_gradle_dependencies = [
     "com.google.android.material:material:1.12.0",
 ]
 
+build_gradle_extra_content="""
+chaquopy.defaultConfig.staticProxy("toga_android.widgets.webview")
+"""
+
 # Web deployment
 [tool.briefcase.app.webview.web]
 requires = [
diff --git a/examples/webview/webview/app.py b/examples/webview/webview/app.py
index 8a9ba98eae..60b5707604 100644
--- a/examples/webview/webview/app.py
+++ b/examples/webview/webview/app.py
@@ -1,7 +1,8 @@
+import asyncio
+
 import toga
 from toga.constants import COLUMN, ROW
 from toga.style import Pack
-import asyncio
 
 
 class ExampleWebView(toga.App):
@@ -26,15 +27,15 @@ def on_webview_load(self, widget, **kwargs):
         self.label.text = "www loaded!"
 
     def on_navigation_starting(self, widget, url):
-        # print(f"on_navigation_starting: {url}")
-        allow = True
-        if !url.startswith(allowed_base_url):
+        print(f"on_navigation_starting: {url}")
+        allow = True
+        if not url.startswith(self.allowed_base_url):
             allow = False
             message = f"Navigation not allowed to: {url}"
             dialog = toga.InfoDialog("on_navigation_starting()", message)
-            task = asyncio.create_task(self.dialog(dialog))
+            asyncio.create_task(self.dialog(dialog))
         return allow
-            
+
     def on_set_url(self, widget, **kwargs):
         self.label.text = "Loading page..."
         self.webview.url = "https://beeware.org/"
diff --git a/winforms/src/toga_winforms/widgets/webview.py b/winforms/src/toga_winforms/widgets/webview.py
index bbf4313f22..ba5d0c7ff1 100644
--- a/winforms/src/toga_winforms/widgets/webview.py
+++ b/winforms/src/toga_winforms/widgets/webview.py
@@ -136,8 +136,10 @@ def winforms_initialization_completed(self, sender, args):
             settings.IsSwipeNavigationEnabled = False
             settings.IsZoomControlEnabled = True
 
-            self.native.CoreWebView2.NavigationStarting += self.winforms_navigation_starting
-            
+            self.native.CoreWebView2.NavigationStarting += (
+                self.winforms_navigation_starting
+            )
+
             for task in self.pending_tasks:
                 task()
             self.pending_tasks = None
@@ -182,7 +184,7 @@ def winforms_navigation_completed(self, sender, args):
             self.loaded_future = None
 
     def winforms_navigation_starting(self, sender, event):
-        print(f"winforms_navigation_starting: {event.Uri}")
+        # print(f"winforms_navigation_starting: {event.Uri}")
         if self.interface.on_navigation_starting:
             allow = self.interface.on_navigation_starting(event.Uri)
             if not allow:

From 4c6777d6cd10190cb40c614c7997ce5e03242dc0 Mon Sep 17 00:00:00 2001
From: Tom Arn <sw@t-arn.com>
Date: Tue, 13 May 2025 14:03:26 +0200
Subject: [PATCH 03/27] * added change note * applied black

---
 changes/3442.feature.rst                      |  1 +
 core/src/toga/widgets/webview.py              | 18 +++++++++---------
 winforms/src/toga_winforms/widgets/webview.py |  1 -
 3 files changed, 10 insertions(+), 10 deletions(-)
 create mode 100644 changes/3442.feature.rst

diff --git a/changes/3442.feature.rst b/changes/3442.feature.rst
new file mode 100644
index 0000000000..af9ff12988
--- /dev/null
+++ b/changes/3442.feature.rst
@@ -0,0 +1 @@
+The WebView widget now supports an on_navigation_starting handler to prevent user-defined URLs from being loaded
diff --git a/core/src/toga/widgets/webview.py b/core/src/toga/widgets/webview.py
index 868463be79..e71a01d1e3 100644
--- a/core/src/toga/widgets/webview.py
+++ b/core/src/toga/widgets/webview.py
@@ -33,7 +33,7 @@ def __init__(
         url: str | None = None,
         content: str | None = None,
         user_agent: str | None = None,
-        on_navigation_starting = None,
+        on_navigation_starting=None,
         on_webview_load: OnWebViewLoadHandler | None = None,
         **kwargs,
     ):
@@ -51,9 +51,9 @@ def __init__(
             value provided for the ``url`` argument will be ignored.
         :param user_agent: The user agent to use for web requests. If not
             provided, the default user agent for the platform will be used.
-        :param on_navigation_starting: A handler that will be invoked when the 
-            web view is requesting permission to navigate or redirect 
-            to a different URI. 
+        :param on_navigation_starting: A handler that will be invoked when the
+            web view is requesting permission to navigate or redirect
+            to a different URI.
         :param on_webview_load: A handler that will be invoked when the web view
             finishes loading.
         :param kwargs: Initial style properties.
@@ -111,10 +111,10 @@ async def load_url(self, url: str) -> asyncio.Future:
 
     @property
     def on_navigation_starting(self):
-        """A handler that will be invoked when the webview is requesting 
+        """A handler that will be invoked when the webview is requesting
         permission to navigate or redirect to a different URI.
-        
-        The handler will receive the arguments `widget` and `url` and must 
+
+        The handler will receive the arguments `widget` and `url` and must
         return True to allow the navigation or False to deny the navigation to the URL.
 
         :returns: The function ``callable`` that is called by this navigation event.
@@ -123,10 +123,10 @@ def on_navigation_starting(self):
 
     @on_navigation_starting.setter
     def on_navigation_starting(self, handler):
-        """Set the handler to invoke when the webview starts navigating """
+        """Set the handler to invoke when the webview starts navigating"""
         if handler and not getattr(self._impl, "SUPPORTS_ON_NAVIGATION_STARTING", True):
             self.factory.not_implemented("WebView.on_navigation_starting")
-        
+
         self._on_navigation_starting = wrapped_handler(self, handler)
         self._impl.set_on_navigation_starting(self._on_navigation_starting)
 
diff --git a/winforms/src/toga_winforms/widgets/webview.py b/winforms/src/toga_winforms/widgets/webview.py
index ba5d0c7ff1..5cf56694f6 100644
--- a/winforms/src/toga_winforms/widgets/webview.py
+++ b/winforms/src/toga_winforms/widgets/webview.py
@@ -41,7 +41,6 @@ def cookies_completion_handler(result):
     """
 
     def _completion_handler(task):
-
         # Initialize a CookieJar to store cookies
         cookie_jar = CookieJar()
 

From 4849755bd8a06e3cfbeaac5151210d9c1c7776c5 Mon Sep 17 00:00:00 2001
From: Tom Arn <sw@t-arn.com>
Date: Tue, 13 May 2025 14:07:19 +0200
Subject: [PATCH 04/27] fixed pre-commit issue

---
 gtk/src/toga_gtk/widgets/webview.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/gtk/src/toga_gtk/widgets/webview.py b/gtk/src/toga_gtk/widgets/webview.py
index ea548e8a35..d35c09b00b 100644
--- a/gtk/src/toga_gtk/widgets/webview.py
+++ b/gtk/src/toga_gtk/widgets/webview.py
@@ -10,6 +10,7 @@
 
 class WebView(Widget):
     """GTK WebView implementation."""
+
     SUPPORTS_ON_NAVIGATION_STARTING = False
 
     def create(self):

From 7f335d69907f549b3d42cc654bc9a6f10bcb2149 Mon Sep 17 00:00:00 2001
From: Tom Arn <sw@t-arn.com>
Date: Tue, 13 May 2025 14:44:17 +0200
Subject: [PATCH 05/27] removed unnecessary set_on_navigation_starting() method

---
 android/src/toga_android/widgets/webview.py   | 4 ----
 core/src/toga/widgets/webview.py              | 1 -
 winforms/src/toga_winforms/widgets/webview.py | 3 ---
 3 files changed, 8 deletions(-)

diff --git a/android/src/toga_android/widgets/webview.py b/android/src/toga_android/widgets/webview.py
index 19f711b77c..3743dcf835 100644
--- a/android/src/toga_android/widgets/webview.py
+++ b/android/src/toga_android/widgets/webview.py
@@ -117,7 +117,3 @@ def evaluate_javascript(self, javascript, on_result=None):
 
         self.native.evaluateJavascript(javascript, ReceiveString(result))
         return result
-
-    def set_on_navigation_starting(self, handler):
-        # print(f"set_on_navigation_starting")
-        pass
diff --git a/core/src/toga/widgets/webview.py b/core/src/toga/widgets/webview.py
index e71a01d1e3..17a7d1e0da 100644
--- a/core/src/toga/widgets/webview.py
+++ b/core/src/toga/widgets/webview.py
@@ -128,7 +128,6 @@ def on_navigation_starting(self, handler):
             self.factory.not_implemented("WebView.on_navigation_starting")
 
         self._on_navigation_starting = wrapped_handler(self, handler)
-        self._impl.set_on_navigation_starting(self._on_navigation_starting)
 
     @property
     def on_webview_load(self) -> OnWebViewLoadHandler:
diff --git a/winforms/src/toga_winforms/widgets/webview.py b/winforms/src/toga_winforms/widgets/webview.py
index 5cf56694f6..4231b8f961 100644
--- a/winforms/src/toga_winforms/widgets/webview.py
+++ b/winforms/src/toga_winforms/widgets/webview.py
@@ -244,9 +244,6 @@ def get_cookies(self):
 
         return result
 
-    def set_on_navigation_starting(self, handler):
-        pass
-
     def evaluate_javascript(self, javascript, on_result=None):
         result = JavaScriptResult(on_result)
         task_scheduler = TaskScheduler.FromCurrentSynchronizationContext()

From a209b71b29dac0de48730e6c24e9b180f6a46bb0 Mon Sep 17 00:00:00 2001
From: Tom Arn <sw@t-arn.com>
Date: Mon, 26 May 2025 08:12:02 +0200
Subject: [PATCH 06/27] * removed unnecessary TogaNavigationEvent * added type
 declaration for handler * added WeakrefCallable wrapper

---
 android/src/toga_android/widgets/webview.py   |  9 ---------
 core/src/toga/widgets/webview.py              | 12 +++++++++++-
 winforms/src/toga_winforms/widgets/webview.py |  2 +-
 3 files changed, 12 insertions(+), 11 deletions(-)

diff --git a/android/src/toga_android/widgets/webview.py b/android/src/toga_android/widgets/webview.py
index 3743dcf835..ac2400d70e 100644
--- a/android/src/toga_android/widgets/webview.py
+++ b/android/src/toga_android/widgets/webview.py
@@ -28,12 +28,6 @@ def onReceiveValue(self, value):
         self.result.set_result(res)
 
 
-class TogaNavigationEvent:
-    def __init__(self, webresourcerequest):
-        self.request = webresourcerequest
-        self.cancel = False
-
-
 class TogaWebClient(static_proxy(WebViewClient)):
     def __init__(self, impl):
         super().__init__()
@@ -42,13 +36,10 @@ def __init__(self, impl):
     @Override(jboolean, [A_WebView, WebResourceRequest])
     def shouldOverrideUrlLoading(self, webview, webresourcerequest):
         if self.webview_impl.interface.on_navigation_starting:
-            event = TogaNavigationEvent(webresourcerequest)
             allow = self.webview_impl.interface.on_navigation_starting(
                 webresourcerequest.getUrl().toString()
             )
             if not allow:
-                event.cancel = True
-                event = None
                 return True
         return False
 
diff --git a/core/src/toga/widgets/webview.py b/core/src/toga/widgets/webview.py
index 17a7d1e0da..efaaf5f7db 100644
--- a/core/src/toga/widgets/webview.py
+++ b/core/src/toga/widgets/webview.py
@@ -25,6 +25,16 @@ def __call__(self, widget: WebView, **kwargs: Any) -> object:
         """
 
 
+class OnNavigationStartingHandler(Protocol):
+    def __call__(self, widget: WebView, **kwargs: Any) -> object:
+        """A handler to invoke when the WebView is requesting permission to navigate or
+        redirect to a different URI.
+
+        :param widget: The WebView
+        :param kwargs: Ensures compatibility with arguments added in future versions.
+        """
+
+
 class WebView(Widget):
     def __init__(
         self,
@@ -33,7 +43,7 @@ def __init__(
         url: str | None = None,
         content: str | None = None,
         user_agent: str | None = None,
-        on_navigation_starting=None,
+        on_navigation_starting: OnNavigationStartingHandler | None = None,
         on_webview_load: OnWebViewLoadHandler | None = None,
         **kwargs,
     ):
diff --git a/winforms/src/toga_winforms/widgets/webview.py b/winforms/src/toga_winforms/widgets/webview.py
index 4231b8f961..cd495b14d6 100644
--- a/winforms/src/toga_winforms/widgets/webview.py
+++ b/winforms/src/toga_winforms/widgets/webview.py
@@ -135,7 +135,7 @@ def winforms_initialization_completed(self, sender, args):
             settings.IsSwipeNavigationEnabled = False
             settings.IsZoomControlEnabled = True
 
-            self.native.CoreWebView2.NavigationStarting += (
+            self.native.CoreWebView2.NavigationStarting += WeakrefCallable(
                 self.winforms_navigation_starting
             )
 

From c6119bab62ec739996aebbd920544555a97cf92f Mon Sep 17 00:00:00 2001
From: Tom Arn <sw@t-arn.com>
Date: Wed, 11 Jun 2025 19:15:52 +0200
Subject: [PATCH 07/27] * windows implementation now supports synchronous and
 asynchronous on_navigation_starting handlers

---
 core/src/toga/widgets/webview.py              | 53 ++++++++++++++++---
 examples/webview/webview/app.py               | 19 +++++--
 winforms/src/toga_winforms/widgets/webview.py | 48 ++++++++++++++++-
 3 files changed, 106 insertions(+), 14 deletions(-)

diff --git a/core/src/toga/widgets/webview.py b/core/src/toga/widgets/webview.py
index efaaf5f7db..318c06ade6 100644
--- a/core/src/toga/widgets/webview.py
+++ b/core/src/toga/widgets/webview.py
@@ -63,7 +63,9 @@ def __init__(
             provided, the default user agent for the platform will be used.
         :param on_navigation_starting: A handler that will be invoked when the
             web view is requesting permission to navigate or redirect
-            to a different URI.
+            to a different URI. The handler can be synchronous or async and must
+            return 1 for allowing the URL, 0 for denying the URL or an awaited
+            QuestionDialog
         :param on_webview_load: A handler that will be invoked when the web view
             finishes loading.
         :param kwargs: Initial style properties.
@@ -72,8 +74,18 @@ def __init__(
 
         self.user_agent = user_agent
 
+        # list for URLs allowed by the user code (usually based on some regex in the
+        # on_navigation_starting handler)
+        self._code_allowed_urls = []
+        # lists for URLs explicitly allowed or denied by the user
+        self._user_allowed_urls = []
+        self._user_denied_urls = []
+        self._url_count = 0
+
         # Set the load handler before loading the first URL.
         self.on_webview_load = on_webview_load
+
+        # Set the handler for URL filtering
         self.on_navigation_starting = on_navigation_starting
 
         # Load both content and root URL if it's provided by the user.
@@ -88,6 +100,8 @@ def _create(self) -> Any:
 
     def _set_url(self, url: str | None, future: asyncio.Future | None) -> None:
         # Utility method for validating and setting the URL with a future.
+        # mark this URL as set from code (for using in on_navigation_starting_handler)
+        self._url_count = 0
         if (url is not None) and not url.startswith(("https://", "http://")):
             raise ValueError("WebView can only display http:// and https:// URLs")
 
@@ -105,6 +119,7 @@ def url(self) -> str | None:
 
     @url.setter
     def url(self, value: str | None) -> None:
+        print(f"webview url.setter: {value}")
         self._set_url(value, future=None)
 
     async def load_url(self, url: str) -> asyncio.Future:
@@ -124,8 +139,9 @@ def on_navigation_starting(self):
         """A handler that will be invoked when the webview is requesting
         permission to navigate or redirect to a different URI.
 
-        The handler will receive the arguments `widget` and `url` and must
-        return True to allow the navigation or False to deny the navigation to the URL.
+        The handler will receive the arguments `widget` and `url` and can
+        be synchronous or async. It must return 1 for allowing the URL,
+        0 for denying the URL or an awaited QuestionDialog
 
         :returns: The function ``callable`` that is called by this navigation event.
         """
@@ -134,10 +150,31 @@ def on_navigation_starting(self):
     @on_navigation_starting.setter
     def on_navigation_starting(self, handler):
         """Set the handler to invoke when the webview starts navigating"""
-        if handler and not getattr(self._impl, "SUPPORTS_ON_NAVIGATION_STARTING", True):
-            self.factory.not_implemented("WebView.on_navigation_starting")
-
-        self._on_navigation_starting = wrapped_handler(self, handler)
+        if handler:
+            if not getattr(self._impl, "SUPPORTS_ON_NAVIGATION_STARTING", True):
+                self.factory.not_implemented("WebView.on_navigation_starting")
+                return
+            self._on_navigation_starting = wrapped_handler(self, handler)
+
+    def on_navigation_starting_callback(self, future, url=None):
+        try:
+            msg = f"on_navigation_starting_callback, url={url}, "
+            msg += f"result={str(future.result())}"
+            print(msg)
+            if future.result() == 1:
+                self._code_allowed_urls.append(url)
+                print(f"Adding code allowed URL={url}")
+                print(f"Navigating to {url}")
+                self.url = url  # navigate to the url
+            elif future.result() is True:
+                self._user_allowed_urls.append(url)
+                print(f"Adding user allowed URL={url}")
+                print(f"Navigating to {url}")
+                self.url = url  # navigate to the url
+            elif future.result() is False:
+                self._user_denied_urls.append(url)
+        except Exception as ex:
+            print(f"on_navigation_starting_callback exception: {str(ex)}")
 
     @property
     def on_webview_load(self) -> OnWebViewLoadHandler:
@@ -186,6 +223,8 @@ def set_content(self, root_url: str, content: str) -> None:
             and used to resolve any relative URLs in the content.
         :param content: The HTML content for the WebView
         """
+        # mark this URL as set from code (for using in on_navigation_starting_handler)
+        self._url_count = 0
         self._impl.set_content(root_url, content)
 
     @property
diff --git a/examples/webview/webview/app.py b/examples/webview/webview/app.py
index 60b5707604..d7f0f1cbf6 100644
--- a/examples/webview/webview/app.py
+++ b/examples/webview/webview/app.py
@@ -26,16 +26,24 @@ def on_bad_js_result(self, result, *, exception=None):
     def on_webview_load(self, widget, **kwargs):
         self.label.text = "www loaded!"
 
-    def on_navigation_starting(self, widget, url):
-        print(f"on_navigation_starting: {url}")
-        allow = True
+    def on_navigation_starting_sync(self, widget, url):
+        print(f"on_navigation_starting_sync: {url}")
+        allow = 1
         if not url.startswith(self.allowed_base_url):
-            allow = False
+            allow = 0
             message = f"Navigation not allowed to: {url}"
             dialog = toga.InfoDialog("on_navigation_starting()", message)
             asyncio.create_task(self.dialog(dialog))
         return allow
 
+    async def on_navigation_starting_async(self, widget, url):
+        print(f"on_navigation_starting_async: {url}")
+        if not url.startswith(self.allowed_base_url):
+            message = f"Do you want to allow navigation to: {url}"
+            dialog = toga.QuestionDialog("on_navigation_starting_async()", message)
+            return await self.main_window.dialog(dialog)
+        return 1
+
     def on_set_url(self, widget, **kwargs):
         self.label.text = "Loading page..."
         self.webview.url = "https://beeware.org/"
@@ -108,7 +116,8 @@ def startup(self):
         )
         # activate web navigation filtering on supported platforms
         if getattr(self.webview._impl, "SUPPORTS_ON_NAVIGATION_STARTING", True):
-            self.webview.on_navigation_starting = self.on_navigation_starting
+            self.webview.on_navigation_starting = self.on_navigation_starting_async
+            # self.webview.on_navigation_starting = self.on_navigation_starting_sync
 
         box = toga.Box(
             children=[
diff --git a/winforms/src/toga_winforms/widgets/webview.py b/winforms/src/toga_winforms/widgets/webview.py
index cd495b14d6..05a8c493e6 100644
--- a/winforms/src/toga_winforms/widgets/webview.py
+++ b/winforms/src/toga_winforms/widgets/webview.py
@@ -1,3 +1,5 @@
+import asyncio
+import functools
 import json
 import webbrowser
 from http.cookiejar import Cookie, CookieJar
@@ -183,10 +185,52 @@ def winforms_navigation_completed(self, sender, args):
             self.loaded_future = None
 
     def winforms_navigation_starting(self, sender, event):
-        # print(f"winforms_navigation_starting: {event.Uri}")
+        print(f"winforms_navigation_starting: {event.Uri}")
+        self.interface._url_count += 1
         if self.interface.on_navigation_starting:
-            allow = self.interface.on_navigation_starting(event.Uri)
+            print("checking URL permission...")
+            if self.interface._url_count == 1:
+                print("Allow the URL set from code")
+                allow = True
+            elif event.Uri in self.interface._code_allowed_urls:
+                # URL is allowed by user on_navigation_starting handler
+                print("URL is allowed by user on_navigation_starting handler")
+                allow = True
+                # prevent the list from growing endlessly
+                self.interface._code_allowed_urls.remove(event.Uri)
+            elif event.Uri in self.interface._user_allowed_urls:
+                # URL is allowed by user interaction
+                print("URL is allowed by user")
+                allow = True
+            elif event.Uri in self.interface._user_denied_urls:
+                # URL is denied by user interaction
+                print("URL is denied by user")
+                allow = False
+            else:
+                result = self.interface.on_navigation_starting(event.Uri)
+                print("winforms_navigation_starting()")
+                if isinstance(result, int):
+                    # on_navigation_starting handler is synchronous
+                    print(f"synchronous handler, result={str(result)}")
+                    allow = True if result == 1 else False
+                elif isinstance(result, asyncio.Future):
+                    # on_navigation_starting handler is asynchronous
+                    if result.done():
+                        allow = result.result()
+                        print(f"asynchronous handler, result={str(allow)}")
+                    else:
+                        # deny the navigation until the user
+                        # or the user on_navigation_starting handler has allowed it
+                        allow = False
+                        print("waiting for permission")
+                        result.add_done_callback(
+                            functools.partial(
+                                self.interface.on_navigation_starting_callback,
+                                url=event.Uri,
+                            )
+                        )
             if not allow:
+                print("Denying navigation")
                 event.Cancel = True
 
     def get_url(self):

From 98ec9fd8485e933e8aa8e72f2ac1c774fc42b226 Mon Sep 17 00:00:00 2001
From: Tom Arn <sw@t-arn.com>
Date: Fri, 13 Jun 2025 16:29:08 +0200
Subject: [PATCH 08/27] refactored the code for Windows to use the cleanup
 method of wrapped_handler

---
 core/src/toga/widgets/webview.py              | 58 +++++++++----------
 examples/webview/webview/app.py               | 12 ++--
 winforms/src/toga_winforms/widgets/webview.py | 38 +++---------
 3 files changed, 43 insertions(+), 65 deletions(-)

diff --git a/core/src/toga/widgets/webview.py b/core/src/toga/widgets/webview.py
index 318c06ade6..e7405c0370 100644
--- a/core/src/toga/widgets/webview.py
+++ b/core/src/toga/widgets/webview.py
@@ -64,7 +64,7 @@ def __init__(
         :param on_navigation_starting: A handler that will be invoked when the
             web view is requesting permission to navigate or redirect
             to a different URI. The handler can be synchronous or async and must
-            return 1 for allowing the URL, 0 for denying the URL or an awaited
+            return True for allowing the URL, False for denying the URL or an awaited
             QuestionDialog
         :param on_webview_load: A handler that will be invoked when the web view
             finishes loading.
@@ -74,13 +74,13 @@ def __init__(
 
         self.user_agent = user_agent
 
-        # list for URLs allowed by the user code (usually based on some regex in the
-        # on_navigation_starting handler)
-        self._code_allowed_urls = []
-        # lists for URLs explicitly allowed or denied by the user
-        self._user_allowed_urls = []
-        self._user_denied_urls = []
+        # If URL is allowed by user interaction or user on_navigation_starting
+        # handler, the count will be set to 0
         self._url_count = 0
+        # For passing the requested URL to the cleanup method of
+        # the user on_navigation_starting async handler. Stays to None for synchronous
+        # handlers
+        self._requested_url = None
 
         # Set the load handler before loading the first URL.
         self.on_webview_load = on_webview_load
@@ -100,8 +100,9 @@ def _create(self) -> Any:
 
     def _set_url(self, url: str | None, future: asyncio.Future | None) -> None:
         # Utility method for validating and setting the URL with a future.
-        # mark this URL as set from code (for using in on_navigation_starting_handler)
-        self._url_count = 0
+        if self.on_navigation_starting:
+            # mark URL as being allowed
+            self._url_count = 0
         if (url is not None) and not url.startswith(("https://", "http://")):
             raise ValueError("WebView can only display http:// and https:// URLs")
 
@@ -119,7 +120,6 @@ def url(self) -> str | None:
 
     @url.setter
     def url(self, value: str | None) -> None:
-        print(f"webview url.setter: {value}")
         self._set_url(value, future=None)
 
     async def load_url(self, url: str) -> asyncio.Future:
@@ -140,39 +140,38 @@ def on_navigation_starting(self):
         permission to navigate or redirect to a different URI.
 
         The handler will receive the arguments `widget` and `url` and can
-        be synchronous or async. It must return 1 for allowing the URL,
-        0 for denying the URL or an awaited QuestionDialog
+        be synchronous or async. It must return True for allowing the URL,
+        False for denying the URL or an awaited QuestionDialog
 
         :returns: The function ``callable`` that is called by this navigation event.
         """
         return self._on_navigation_starting
 
     @on_navigation_starting.setter
-    def on_navigation_starting(self, handler):
+    def on_navigation_starting(self, handler, url=url):
         """Set the handler to invoke when the webview starts navigating"""
+        self._on_navigation_starting = None
         if handler:
             if not getattr(self._impl, "SUPPORTS_ON_NAVIGATION_STARTING", True):
                 self.factory.not_implemented("WebView.on_navigation_starting")
                 return
-            self._on_navigation_starting = wrapped_handler(self, handler)
+            self._on_navigation_starting = wrapped_handler(
+                self, handler, cleanup=self.on_navigation_starting_callback
+            )
 
-    def on_navigation_starting_callback(self, future, url=None):
+    def on_navigation_starting_callback(self, widget, result):
         try:
+            url = widget._requested_url
             msg = f"on_navigation_starting_callback, url={url}, "
-            msg += f"result={str(future.result())}"
+            msg += f"result={str(result)}"
             print(msg)
-            if future.result() == 1:
-                self._code_allowed_urls.append(url)
-                print(f"Adding code allowed URL={url}")
-                print(f"Navigating to {url}")
-                self.url = url  # navigate to the url
-            elif future.result() is True:
-                self._user_allowed_urls.append(url)
-                print(f"Adding user allowed URL={url}")
+            if url is None:
+                # The user on_navigation_handler is synchronous - do nothing
+                return
+            if result is True:
                 print(f"Navigating to {url}")
-                self.url = url  # navigate to the url
-            elif future.result() is False:
-                self._user_denied_urls.append(url)
+                # navigate to the url, the URL will automatically be marked as allowed
+                self.url = url
         except Exception as ex:
             print(f"on_navigation_starting_callback exception: {str(ex)}")
 
@@ -223,8 +222,9 @@ def set_content(self, root_url: str, content: str) -> None:
             and used to resolve any relative URLs in the content.
         :param content: The HTML content for the WebView
         """
-        # mark this URL as set from code (for using in on_navigation_starting_handler)
-        self._url_count = 0
+        if self.on_navigation_starting:
+            # mark URL as being allowed
+            self._url_count = 0
         self._impl.set_content(root_url, content)
 
     @property
diff --git a/examples/webview/webview/app.py b/examples/webview/webview/app.py
index d7f0f1cbf6..be04af731d 100644
--- a/examples/webview/webview/app.py
+++ b/examples/webview/webview/app.py
@@ -28,9 +28,9 @@ def on_webview_load(self, widget, **kwargs):
 
     def on_navigation_starting_sync(self, widget, url):
         print(f"on_navigation_starting_sync: {url}")
-        allow = 1
+        allow = True
         if not url.startswith(self.allowed_base_url):
-            allow = 0
+            allow = False
             message = f"Navigation not allowed to: {url}"
             dialog = toga.InfoDialog("on_navigation_starting()", message)
             asyncio.create_task(self.dialog(dialog))
@@ -42,7 +42,7 @@ async def on_navigation_starting_async(self, widget, url):
             message = f"Do you want to allow navigation to: {url}"
             dialog = toga.QuestionDialog("on_navigation_starting_async()", message)
             return await self.main_window.dialog(dialog)
-        return 1
+        return True
 
     def on_set_url(self, widget, **kwargs):
         self.label.text = "Loading page..."
@@ -113,11 +113,9 @@ def startup(self):
             url="https://beeware.org/",
             on_webview_load=self.on_webview_load,
             style=Pack(flex=1),
+            # on_navigation_starting=self.on_navigation_starting_async,
+            on_navigation_starting=self.on_navigation_starting_sync,
         )
-        # activate web navigation filtering on supported platforms
-        if getattr(self.webview._impl, "SUPPORTS_ON_NAVIGATION_STARTING", True):
-            self.webview.on_navigation_starting = self.on_navigation_starting_async
-            # self.webview.on_navigation_starting = self.on_navigation_starting_sync
 
         box = toga.Box(
             children=[
diff --git a/winforms/src/toga_winforms/widgets/webview.py b/winforms/src/toga_winforms/widgets/webview.py
index 05a8c493e6..48c6a82955 100644
--- a/winforms/src/toga_winforms/widgets/webview.py
+++ b/winforms/src/toga_winforms/widgets/webview.py
@@ -1,5 +1,4 @@
 import asyncio
-import functools
 import json
 import webbrowser
 from http.cookiejar import Cookie, CookieJar
@@ -186,49 +185,30 @@ def winforms_navigation_completed(self, sender, args):
 
     def winforms_navigation_starting(self, sender, event):
         print(f"winforms_navigation_starting: {event.Uri}")
-        self.interface._url_count += 1
         if self.interface.on_navigation_starting:
             print("checking URL permission...")
+            self.interface._url_count += 1
             if self.interface._url_count == 1:
-                print("Allow the URL set from code")
+                # URL is allowed by user code
+                print("URL is allowed by user code")
                 allow = True
-            elif event.Uri in self.interface._code_allowed_urls:
-                # URL is allowed by user on_navigation_starting handler
-                print("URL is allowed by user on_navigation_starting handler")
-                allow = True
-                # prevent the list from growing endlessly
-                self.interface._code_allowed_urls.remove(event.Uri)
-            elif event.Uri in self.interface._user_allowed_urls:
-                # URL is allowed by user interaction
-                print("URL is allowed by user")
-                allow = True
-            elif event.Uri in self.interface._user_denied_urls:
-                # URL is denied by user interaction
-                print("URL is denied by user")
-                allow = False
             else:
-                result = self.interface.on_navigation_starting(event.Uri)
-                print("winforms_navigation_starting()")
-                if isinstance(result, int):
+                result = self.interface.on_navigation_starting(url=event.Uri)
+                if isinstance(result, bool):
                     # on_navigation_starting handler is synchronous
                     print(f"synchronous handler, result={str(result)}")
-                    allow = True if result == 1 else False
+                    allow = result
                 elif isinstance(result, asyncio.Future):
                     # on_navigation_starting handler is asynchronous
+                    self.interface._requested_url = event.Uri
                     if result.done():
                         allow = result.result()
                         print(f"asynchronous handler, result={str(allow)}")
                     else:
-                        # deny the navigation until the user
-                        # or the user on_navigation_starting handler has allowed it
+                        # deny the navigation until the user himself or the user
+                        # defined on_navigation_starting handler has allowed it
                         allow = False
                         print("waiting for permission")
-                        result.add_done_callback(
-                            functools.partial(
-                                self.interface.on_navigation_starting_callback,
-                                url=event.Uri,
-                            )
-                        )
             if not allow:
                 print("Denying navigation")
                 event.Cancel = True

From 39af7627825c308714923872e7fb2b32e0c023e0 Mon Sep 17 00:00:00 2001
From: Tom Arn <sw@t-arn.com>
Date: Mon, 16 Jun 2025 17:18:39 +0200
Subject: [PATCH 09/27] defined on_navigation_starting cleanup method as inner
 method

---
 core/src/toga/widgets/webview.py              | 42 +++++++++----------
 examples/webview/webview/app.py               |  4 +-
 winforms/src/toga_winforms/widgets/webview.py |  2 +-
 3 files changed, 23 insertions(+), 25 deletions(-)

diff --git a/core/src/toga/widgets/webview.py b/core/src/toga/widgets/webview.py
index e7405c0370..61caeaaee4 100644
--- a/core/src/toga/widgets/webview.py
+++ b/core/src/toga/widgets/webview.py
@@ -77,10 +77,6 @@ def __init__(
         # If URL is allowed by user interaction or user on_navigation_starting
         # handler, the count will be set to 0
         self._url_count = 0
-        # For passing the requested URL to the cleanup method of
-        # the user on_navigation_starting async handler. Stays to None for synchronous
-        # handlers
-        self._requested_url = None
 
         # Set the load handler before loading the first URL.
         self.on_webview_load = on_webview_load
@@ -148,33 +144,35 @@ def on_navigation_starting(self):
         return self._on_navigation_starting
 
     @on_navigation_starting.setter
-    def on_navigation_starting(self, handler, url=url):
+    def on_navigation_starting(self, handler, url=None):
         """Set the handler to invoke when the webview starts navigating"""
+
+        def cleanup(widget, result):
+            try:
+                msg = f"on_navigation_starting.cleanup, url={url}, "
+                msg += f"result={str(result)}"
+                print(msg)
+                print(f"widget._requested_url={widget._requested_url}")
+                if url is None:
+                    # The user on_navigation_handler is synchronous - do nothing
+                    return
+                if result is True:
+                    print(f"Navigating to {url}")
+                    # navigate to the url, the URL will automatically be marked
+                    # as allowed
+                    self.url = url
+            except Exception as ex:
+                print(f"on_navigation_starting.cleanup exception: {str(ex)}")
+
         self._on_navigation_starting = None
         if handler:
             if not getattr(self._impl, "SUPPORTS_ON_NAVIGATION_STARTING", True):
                 self.factory.not_implemented("WebView.on_navigation_starting")
                 return
             self._on_navigation_starting = wrapped_handler(
-                self, handler, cleanup=self.on_navigation_starting_callback
+                self, handler, cleanup=cleanup
             )
 
-    def on_navigation_starting_callback(self, widget, result):
-        try:
-            url = widget._requested_url
-            msg = f"on_navigation_starting_callback, url={url}, "
-            msg += f"result={str(result)}"
-            print(msg)
-            if url is None:
-                # The user on_navigation_handler is synchronous - do nothing
-                return
-            if result is True:
-                print(f"Navigating to {url}")
-                # navigate to the url, the URL will automatically be marked as allowed
-                self.url = url
-        except Exception as ex:
-            print(f"on_navigation_starting_callback exception: {str(ex)}")
-
     @property
     def on_webview_load(self) -> OnWebViewLoadHandler:
         """The handler to invoke when the web view finishes loading.
diff --git a/examples/webview/webview/app.py b/examples/webview/webview/app.py
index be04af731d..4578eca064 100644
--- a/examples/webview/webview/app.py
+++ b/examples/webview/webview/app.py
@@ -113,8 +113,8 @@ def startup(self):
             url="https://beeware.org/",
             on_webview_load=self.on_webview_load,
             style=Pack(flex=1),
-            # on_navigation_starting=self.on_navigation_starting_async,
-            on_navigation_starting=self.on_navigation_starting_sync,
+            on_navigation_starting=self.on_navigation_starting_async,
+            # on_navigation_starting=self.on_navigation_starting_sync,
         )
 
         box = toga.Box(
diff --git a/winforms/src/toga_winforms/widgets/webview.py b/winforms/src/toga_winforms/widgets/webview.py
index 48c6a82955..a84d38f9c7 100644
--- a/winforms/src/toga_winforms/widgets/webview.py
+++ b/winforms/src/toga_winforms/widgets/webview.py
@@ -200,7 +200,7 @@ def winforms_navigation_starting(self, sender, event):
                     allow = result
                 elif isinstance(result, asyncio.Future):
                     # on_navigation_starting handler is asynchronous
-                    self.interface._requested_url = event.Uri
+                    self.interface._requested_url = event.Uri  # should not be needed
                     if result.done():
                         allow = result.result()
                         print(f"asynchronous handler, result={str(allow)}")

From 44814b21424b07be0552a581a1216fca768514fa Mon Sep 17 00:00:00 2001
From: Tom Arn <sw@t-arn.com>
Date: Wed, 5 Nov 2025 09:42:36 +0100
Subject: [PATCH 10/27] extended wrapped_handler and handler_with_cleanup to
 pass kwargs to the cleanup method

---
 core/src/toga/handlers.py                     | 4 ++--
 core/src/toga/widgets/webview.py              | 6 +++---
 examples/webview/webview/app.py               | 6 ++++--
 winforms/src/toga_winforms/widgets/webview.py | 1 -
 4 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/core/src/toga/handlers.py b/core/src/toga/handlers.py
index 20b829a1d8..bf963d4b47 100644
--- a/core/src/toga/handlers.py
+++ b/core/src/toga/handlers.py
@@ -86,7 +86,7 @@ async def handler_with_cleanup(
     else:
         if cleanup:
             try:
-                cleanup(interface, result)
+                cleanup(interface, result, **kwargs)
             except Exception as e:
                 print("Error in async handler cleanup:", e, file=sys.stderr)
                 traceback.print_exc()
@@ -170,7 +170,7 @@ def _handler(*args: object, **kwargs: object) -> object:
                     else:
                         try:
                             if cleanup:
-                                cleanup(interface, result)
+                                cleanup(interface, result, **kwargs)
                             return result
                         except Exception as e:
                             print("Error in handler cleanup:", e, file=sys.stderr)
diff --git a/core/src/toga/widgets/webview.py b/core/src/toga/widgets/webview.py
index 61caeaaee4..20961db0d3 100644
--- a/core/src/toga/widgets/webview.py
+++ b/core/src/toga/widgets/webview.py
@@ -144,15 +144,15 @@ def on_navigation_starting(self):
         return self._on_navigation_starting
 
     @on_navigation_starting.setter
-    def on_navigation_starting(self, handler, url=None):
+    def on_navigation_starting(self, handler):
         """Set the handler to invoke when the webview starts navigating"""
 
-        def cleanup(widget, result):
+        def cleanup(widget, result, **kwargs):
+            url = kwargs.get("url", None)
             try:
                 msg = f"on_navigation_starting.cleanup, url={url}, "
                 msg += f"result={str(result)}"
                 print(msg)
-                print(f"widget._requested_url={widget._requested_url}")
                 if url is None:
                     # The user on_navigation_handler is synchronous - do nothing
                     return
diff --git a/examples/webview/webview/app.py b/examples/webview/webview/app.py
index 4578eca064..c2fe7b0363 100644
--- a/examples/webview/webview/app.py
+++ b/examples/webview/webview/app.py
@@ -26,7 +26,8 @@ def on_bad_js_result(self, result, *, exception=None):
     def on_webview_load(self, widget, **kwargs):
         self.label.text = "www loaded!"
 
-    def on_navigation_starting_sync(self, widget, url):
+    def on_navigation_starting_sync(self, widget, **kwargs):
+        url = kwargs.get("url", None)
         print(f"on_navigation_starting_sync: {url}")
         allow = True
         if not url.startswith(self.allowed_base_url):
@@ -36,7 +37,8 @@ def on_navigation_starting_sync(self, widget, url):
             asyncio.create_task(self.dialog(dialog))
         return allow
 
-    async def on_navigation_starting_async(self, widget, url):
+    async def on_navigation_starting_async(self, widget, **kwargs):
+        url = kwargs.get("url", "No URL awailable")
         print(f"on_navigation_starting_async: {url}")
         if not url.startswith(self.allowed_base_url):
             message = f"Do you want to allow navigation to: {url}"
diff --git a/winforms/src/toga_winforms/widgets/webview.py b/winforms/src/toga_winforms/widgets/webview.py
index a84d38f9c7..c941dee625 100644
--- a/winforms/src/toga_winforms/widgets/webview.py
+++ b/winforms/src/toga_winforms/widgets/webview.py
@@ -200,7 +200,6 @@ def winforms_navigation_starting(self, sender, event):
                     allow = result
                 elif isinstance(result, asyncio.Future):
                     # on_navigation_starting handler is asynchronous
-                    self.interface._requested_url = event.Uri  # should not be needed
                     if result.done():
                         allow = result.result()
                         print(f"asynchronous handler, result={str(allow)}")

From 951a94b9407ba9e1836128087be99d4c7b522954 Mon Sep 17 00:00:00 2001
From: Tom Arn <sw@t-arn.com>
Date: Wed, 5 Nov 2025 09:50:54 +0100
Subject: [PATCH 11/27] Renamed the class of the WebView example to match the
 current code

---
 examples/webview/webview/app.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/examples/webview/webview/app.py b/examples/webview/webview/app.py
index c2fe7b0363..6e63db92fd 100644
--- a/examples/webview/webview/app.py
+++ b/examples/webview/webview/app.py
@@ -5,7 +5,7 @@
 from toga.style import Pack
 
 
-class ExampleWebView(toga.App):
+class WebViewApp(toga.App):
     allowed_base_url = "https://beeware.org/"
 
     async def on_do_async_js(self, widget, **kwargs):
@@ -133,7 +133,7 @@ def startup(self):
 
 
 def main():
-    return ExampleWebView("Toga WebView Demo", "org.beeware.toga.examples.webview")
+    return WebViewApp("Toga WebView Demo", "org.beeware.toga.examples.webview")
 
 
 if __name__ == "__main__":

From d7751b23703a7bdf02c84d408e70778619049252 Mon Sep 17 00:00:00 2001
From: Tom Arn <sw@t-arn.com>
Date: Fri, 7 Nov 2025 07:06:27 +0100
Subject: [PATCH 12/27] * fixed calling the on_navigation_starting handler on
 Android

---
 android/src/toga_android/widgets/webview.py | 2 +-
 examples/webview/webview/app.py             | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/android/src/toga_android/widgets/webview.py b/android/src/toga_android/widgets/webview.py
index ac2400d70e..db2903e09a 100644
--- a/android/src/toga_android/widgets/webview.py
+++ b/android/src/toga_android/widgets/webview.py
@@ -37,7 +37,7 @@ def __init__(self, impl):
     def shouldOverrideUrlLoading(self, webview, webresourcerequest):
         if self.webview_impl.interface.on_navigation_starting:
             allow = self.webview_impl.interface.on_navigation_starting(
-                webresourcerequest.getUrl().toString()
+                url=webresourcerequest.getUrl().toString()
             )
             if not allow:
                 return True
diff --git a/examples/webview/webview/app.py b/examples/webview/webview/app.py
index 6e63db92fd..b324620364 100644
--- a/examples/webview/webview/app.py
+++ b/examples/webview/webview/app.py
@@ -115,8 +115,8 @@ def startup(self):
             url="https://beeware.org/",
             on_webview_load=self.on_webview_load,
             style=Pack(flex=1),
-            on_navigation_starting=self.on_navigation_starting_async,
-            # on_navigation_starting=self.on_navigation_starting_sync,
+            # on_navigation_starting=self.on_navigation_starting_async,
+            on_navigation_starting=self.on_navigation_starting_sync,
         )
 
         box = toga.Box(

From 883060703ba2e175787a98ed946a256de62ca88b Mon Sep 17 00:00:00 2001
From: Tom Arn <sw@t-arn.com>
Date: Mon, 10 Nov 2025 17:50:40 +0100
Subject: [PATCH 13/27] * fixed app crash on Android when staticProxy setting
 is missing in pyproject.toml * improve docstring for on_navigation_starting *
 updated app.py to include the latest changes from main

---
 android/src/toga_android/widgets/webview.py   | 37 +++++++------------
 .../widgets/webview_static_proxy.py           | 21 +++++++++++
 core/src/toga/widgets/webview.py              |  9 +++--
 examples/webview/webview/app.py               | 32 +++++++++-------
 4 files changed, 57 insertions(+), 42 deletions(-)
 create mode 100644 android/src/toga_android/widgets/webview_static_proxy.py

diff --git a/android/src/toga_android/widgets/webview.py b/android/src/toga_android/widgets/webview.py
index db2903e09a..466681b9c9 100644
--- a/android/src/toga_android/widgets/webview.py
+++ b/android/src/toga_android/widgets/webview.py
@@ -1,13 +1,8 @@
 import json
 from http.cookiejar import CookieJar
 
-from android.webkit import (
-    ValueCallback,
-    WebResourceRequest,
-    WebView as A_WebView,
-    WebViewClient,
-)
-from java import Override, dynamic_proxy, jboolean, static_proxy
+from android.webkit import ValueCallback, WebView as A_WebView, WebViewClient
+from java import dynamic_proxy
 
 from toga.widgets.webview import CookiesResult, JavaScriptResult
 
@@ -28,30 +23,24 @@ def onReceiveValue(self, value):
         self.result.set_result(res)
 
 
-class TogaWebClient(static_proxy(WebViewClient)):
-    def __init__(self, impl):
-        super().__init__()
-        self.webview_impl = impl
-
-    @Override(jboolean, [A_WebView, WebResourceRequest])
-    def shouldOverrideUrlLoading(self, webview, webresourcerequest):
-        if self.webview_impl.interface.on_navigation_starting:
-            allow = self.webview_impl.interface.on_navigation_starting(
-                url=webresourcerequest.getUrl().toString()
-            )
-            if not allow:
-                return True
-        return False
-
-
 class WebView(Widget):
     SUPPORTS_ON_WEBVIEW_LOAD = False
 
     def create(self):
         self.native = A_WebView(self._native_activity)
+        try:
+            from .webview_static_proxy import TogaWebClient
+
+            client = TogaWebClient(self)
+        except BaseException:
+            client = WebViewClient()
+            msg = "chaquopy.defaultConfig.staticProxy"
+            msg += '("toga_android.widgets.webview_static_proxy") '
+            msg += 'missing in pyproject.toml section "build_gradle_extra_content"\n'
+            msg += "on_navigation_starting handler is therefore not available"
+            print(msg)
         # Set a WebViewClient so that new links open in this activity,
         # rather than triggering the phone's web browser.
-        client = TogaWebClient(self)
         self.native.setWebViewClient(client)
 
         self.settings = self.native.getSettings()
diff --git a/android/src/toga_android/widgets/webview_static_proxy.py b/android/src/toga_android/widgets/webview_static_proxy.py
new file mode 100644
index 0000000000..177571d0cb
--- /dev/null
+++ b/android/src/toga_android/widgets/webview_static_proxy.py
@@ -0,0 +1,21 @@
+from android.webkit import WebResourceRequest, WebView as A_WebView, WebViewClient
+from java import Override, jboolean, static_proxy
+
+
+class TogaWebClient(static_proxy(WebViewClient)):
+    def __init__(self, impl):
+        super().__init__()
+        self.webview_impl = impl
+
+    @Override(jboolean, [A_WebView, WebResourceRequest])
+    def shouldOverrideUrlLoading(self, webview, webresourcerequest):
+        if self.webview_impl.interface.on_navigation_starting:
+            allow = self.webview_impl.interface.on_navigation_starting(
+                url=webresourcerequest.getUrl().toString()
+            )
+            if not allow:
+                return True
+        return False
+
+
+# TogaWebClient
diff --git a/core/src/toga/widgets/webview.py b/core/src/toga/widgets/webview.py
index 20961db0d3..e3822cc874 100644
--- a/core/src/toga/widgets/webview.py
+++ b/core/src/toga/widgets/webview.py
@@ -133,11 +133,12 @@ async def load_url(self, url: str) -> asyncio.Future:
     @property
     def on_navigation_starting(self):
         """A handler that will be invoked when the webview is requesting
-        permission to navigate or redirect to a different URI.
+        permission to navigate or redirect to a different URI. This feature is
+        currently only supported on Windows and Android.
 
-        The handler will receive the arguments `widget` and `url` and can
-        be synchronous or async. It must return True for allowing the URL,
-        False for denying the URL or an awaited QuestionDialog
+        The handler will receive the positional argument `widget` and the keyword
+        argument `url` and can be synchronous or async. It must return True for
+        allowing the URL, False for denying the URL or an awaited QuestionDialog
 
         :returns: The function ``callable`` that is called by this navigation event.
         """
diff --git a/examples/webview/webview/app.py b/examples/webview/webview/app.py
index b324620364..34f1ab05eb 100644
--- a/examples/webview/webview/app.py
+++ b/examples/webview/webview/app.py
@@ -2,7 +2,6 @@
 
 import toga
 from toga.constants import COLUMN, ROW
-from toga.style import Pack
 
 
 class WebViewApp(toga.App):
@@ -17,10 +16,13 @@ def on_good_js(self, widget, **kwargs):
             "+ navigator.userAgent;"
         )
 
-    def on_bad_js(self, widget, **kwargs):
-        self.webview.evaluate_javascript("invalid js", on_result=self.on_bad_js_result)
-
-    def on_bad_js_result(self, result, *, exception=None):
+    async def on_bad_js(self, widget, **kwargs):
+        try:
+            result = await self.webview.evaluate_javascript("invalid js")
+            exception = None
+        except Exception as exc:
+            result = None
+            exception = exc
         self.label.text = f"{result=!r}, {exception=!r}"
 
     def on_webview_load(self, widget, **kwargs):
@@ -78,12 +80,12 @@ def on_set_agent(self, widget, **kwargs):
 
     def startup(self):
         self.main_window = toga.MainWindow()
-        self.label = toga.Label("www is loading |", style=Pack(flex=1, margin=5))
+        self.label = toga.Label("www is loading |", flex=1, margin=5)
 
         button_box = toga.Box(
             children=[
                 toga.Box(
-                    style=Pack(direction=ROW),
+                    direction=ROW,
                     children=[
                         toga.Button("set URL", on_press=self.on_set_url),
                         toga.Button("load URL", on_press=self.on_load_url),
@@ -92,7 +94,7 @@ def startup(self):
                     ],
                 ),
                 toga.Box(
-                    style=Pack(direction=ROW),
+                    direction=ROW,
                     children=[
                         toga.Button("2 + 2", on_press=self.on_do_async_js),
                         toga.Button("good js", on_press=self.on_good_js),
@@ -101,20 +103,22 @@ def startup(self):
                     ],
                 ),
                 toga.Box(
-                    style=Pack(direction=ROW),
+                    direction=ROW,
                     children=[
                         toga.Button("set agent", on_press=self.on_set_agent),
                         toga.Button("get agent", on_press=self.on_get_agent),
                     ],
                 ),
             ],
-            style=Pack(flex=0, direction=COLUMN, margin=5),
+            flex=0,
+            direction=COLUMN,
+            margin=5,
         )
 
         self.webview = toga.WebView(
             url="https://beeware.org/",
             on_webview_load=self.on_webview_load,
-            style=Pack(flex=1),
+            flex=1,
             # on_navigation_starting=self.on_navigation_starting_async,
             on_navigation_starting=self.on_navigation_starting_sync,
         )
@@ -125,7 +129,8 @@ def startup(self):
                 self.label,
                 self.webview,
             ],
-            style=Pack(flex=1, direction=COLUMN),
+            flex=1,
+            direction=COLUMN,
         )
 
         self.main_window.content = box
@@ -137,5 +142,4 @@ def main():
 
 
 if __name__ == "__main__":
-    app = main()
-    app.main_loop()
+    main().main_loop()

From 0483945a0ddbf3ed8fdcbf6537b78898eafc7b38 Mon Sep 17 00:00:00 2001
From: Tom Arn <sw@t-arn.com>
Date: Mon, 10 Nov 2025 18:49:07 +0100
Subject: [PATCH 14/27] fixed staticProxy in pyproject.toml

---
 examples/webview/pyproject.toml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/examples/webview/pyproject.toml b/examples/webview/pyproject.toml
index edfb984bb5..630e812dcc 100644
--- a/examples/webview/pyproject.toml
+++ b/examples/webview/pyproject.toml
@@ -54,7 +54,7 @@ build_gradle_dependencies = [
 ]
 
 build_gradle_extra_content="""
-chaquopy.defaultConfig.staticProxy("toga_android.widgets.webview")
+chaquopy.defaultConfig.staticProxy("toga_android.widgets.webview_static_proxy")
 """
 
 # Web deployment

From 6fde3616d8916b02ae23e9d6ce1a77e922bdada7 Mon Sep 17 00:00:00 2001
From: Tom Arn <sw@t-arn.com>
Date: Mon, 17 Nov 2025 17:33:47 +0100
Subject: [PATCH 15/27] adjusted test_handlers.py for the changed cleanup
 handler

---
 core/tests/test_handlers.py | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/core/tests/test_handlers.py b/core/tests/test_handlers.py
index 79cbf0bd5c..62bc8e2553 100644
--- a/core/tests/test_handlers.py
+++ b/core/tests/test_handlers.py
@@ -148,7 +148,7 @@ def handler(*args, **kwargs):
     }
 
     # Cleanup method was invoked
-    cleanup.assert_called_once_with(obj, 42)
+    cleanup.assert_called_once_with(obj, 42, kwarg1=3, kwarg2=4)
 
 
 def test_function_handler_with_cleanup_error(capsys):
@@ -177,7 +177,7 @@ def handler(*args, **kwargs):
     }
 
     # Cleanup method was invoked
-    cleanup.assert_called_once_with(obj, 42)
+    cleanup.assert_called_once_with(obj, 42, kwarg1=3, kwarg2=4)
 
     # Evidence of the handler cleanup error is in the log.
     assert (
@@ -439,7 +439,7 @@ async def handler(*args, **kwargs):
     }
 
     # Cleanup method was invoked
-    cleanup.assert_called_once_with(obj, 42)
+    cleanup.assert_called_once_with(obj, 42, kwarg1=3, kwarg2=4)
 
 
 async def test_coroutine_handler_with_cleanup_error(capsys):
@@ -471,7 +471,7 @@ async def handler(*args, **kwargs):
     }
 
     # Cleanup method was invoked
-    cleanup.assert_called_once_with(obj, 42)
+    cleanup.assert_called_once_with(obj, 42, kwarg1=3, kwarg2=4)
 
     # Evidence of the handler cleanup error is in the log.
     assert (

From 2251c6deb50ed1a39f2287df30dbf2edf6e9800f Mon Sep 17 00:00:00 2001
From: Tom Arn <sw@t-arn.com>
Date: Tue, 18 Nov 2025 00:02:35 +0100
Subject: [PATCH 16/27] Applied changes as requested by review

---
 android/src/toga_android/widgets/webview.py    | 18 ++++++++++++------
 .../widgets/webview_static_proxy.py            |  3 ---
 core/src/toga/handlers.py                      |  2 +-
 core/src/toga/widgets/webview.py               | 14 ++++++--------
 winforms/src/toga_winforms/widgets/webview.py  |  5 +++--
 5 files changed, 22 insertions(+), 20 deletions(-)

diff --git a/android/src/toga_android/widgets/webview.py b/android/src/toga_android/widgets/webview.py
index 466681b9c9..d876c91263 100644
--- a/android/src/toga_android/widgets/webview.py
+++ b/android/src/toga_android/widgets/webview.py
@@ -1,8 +1,10 @@
 import json
 from http.cookiejar import CookieJar
 
+
 from android.webkit import ValueCallback, WebView as A_WebView, WebViewClient
 from java import dynamic_proxy
+from java.lang import NoClassDefFoundError
 
 from toga.widgets.webview import CookiesResult, JavaScriptResult
 
@@ -32,13 +34,17 @@ def create(self):
             from .webview_static_proxy import TogaWebClient
 
             client = TogaWebClient(self)
-        except BaseException:
+        except NoClassDefFoundError:
             client = WebViewClient()
-            msg = "chaquopy.defaultConfig.staticProxy"
-            msg += '("toga_android.widgets.webview_static_proxy") '
-            msg += 'missing in pyproject.toml section "build_gradle_extra_content"\n'
-            msg += "on_navigation_starting handler is therefore not available"
-            print(msg)
+            if self.interface.on_navigation_starting:
+                import sys
+                print(
+                    'chaquopy.defaultConfig.staticProxy'
+                    '("toga_android.widgets.webview_static_proxy") '
+                    'missing in pyproject.toml section "build_gradle_extra_content". '
+                    'on_navigation_starting handler is therefore not available',
+                    file=sys.stderr
+                )
         # Set a WebViewClient so that new links open in this activity,
         # rather than triggering the phone's web browser.
         self.native.setWebViewClient(client)
diff --git a/android/src/toga_android/widgets/webview_static_proxy.py b/android/src/toga_android/widgets/webview_static_proxy.py
index 177571d0cb..85f9af10e8 100644
--- a/android/src/toga_android/widgets/webview_static_proxy.py
+++ b/android/src/toga_android/widgets/webview_static_proxy.py
@@ -16,6 +16,3 @@ def shouldOverrideUrlLoading(self, webview, webresourcerequest):
             if not allow:
                 return True
         return False
-
-
-# TogaWebClient
diff --git a/core/src/toga/handlers.py b/core/src/toga/handlers.py
index 064843023e..7e11eaecf2 100644
--- a/core/src/toga/handlers.py
+++ b/core/src/toga/handlers.py
@@ -87,7 +87,7 @@ async def handler_with_cleanup(
     else:
         if cleanup:
             try:
-                cleanup(interface, result, **kwargs)
+                cleanup(interface, result, *args, **kwargs)
             except Exception as e:
                 print("Error in async handler cleanup:", e, file=sys.stderr)
                 traceback.print_exc()
diff --git a/core/src/toga/widgets/webview.py b/core/src/toga/widgets/webview.py
index dd5906ddfa..b1cb0ff22d 100644
--- a/core/src/toga/widgets/webview.py
+++ b/core/src/toga/widgets/webview.py
@@ -73,10 +73,10 @@ def __init__(
         super().__init__(id, style, **kwargs)
 
         self.user_agent = user_agent
-
+        
         # If URL is allowed by user interaction or user on_navigation_starting
-        # handler, the count will be set to 0
-        self._url_count = 0
+        # handler, this attribute is True
+        self._url_allowed = True
 
         # Set the load handler before loading the first URL.
         self.on_webview_load = on_webview_load
@@ -98,7 +98,7 @@ def _set_url(self, url: str | None, future: asyncio.Future | None) -> None:
         # Utility method for validating and setting the URL with a future.
         if self.on_navigation_starting:
             # mark URL as being allowed
-            self._url_count = 0
+            self._url_allowed = True
         if (url is not None) and not url.startswith(("https://", "http://")):
             raise ValueError("WebView can only display http:// and https:// URLs")
 
@@ -133,7 +133,7 @@ async def load_url(self, url: str) -> asyncio.Future:
         return await loaded_future
 
     @property
-    def on_navigation_starting(self):
+    def on_navigation_starting(self) -> OnNavigationStartingHandler:
         """A handler that will be invoked when the webview is requesting
         permission to navigate or redirect to a different URI. This feature is
         currently only supported on Windows and Android.
@@ -141,8 +141,6 @@ def on_navigation_starting(self):
         The handler will receive the positional argument `widget` and the keyword
         argument `url` and can be synchronous or async. It must return True for
         allowing the URL, False for denying the URL or an awaited QuestionDialog
-
-        :returns: The function ``callable`` that is called by this navigation event.
         """
         return self._on_navigation_starting
 
@@ -225,7 +223,7 @@ def set_content(self, root_url: str, content: str) -> None:
         """
         if self.on_navigation_starting:
             # mark URL as being allowed
-            self._url_count = 0
+            self._url_allowed = True
         self._impl.set_content(root_url, content)
 
     @property
diff --git a/winforms/src/toga_winforms/widgets/webview.py b/winforms/src/toga_winforms/widgets/webview.py
index ad73272f87..1597dcd686 100644
--- a/winforms/src/toga_winforms/widgets/webview.py
+++ b/winforms/src/toga_winforms/widgets/webview.py
@@ -187,11 +187,12 @@ def winforms_navigation_starting(self, sender, event):
         print(f"winforms_navigation_starting: {event.Uri}")
         if self.interface.on_navigation_starting:
             print("checking URL permission...")
-            self.interface._url_count += 1
-            if self.interface._url_count == 1:
+            if self.interface._url_allowed:
                 # URL is allowed by user code
                 print("URL is allowed by user code")
                 allow = True
+                # allow the URL only this time
+                self.interface._url_allowed = False
             else:
                 result = self.interface.on_navigation_starting(url=event.Uri)
                 if isinstance(result, bool):

From 0c9072f6a4ee53d0d6e824a43f80987c4c163477 Mon Sep 17 00:00:00 2001
From: Tom Arn <sw@t-arn.com>
Date: Tue, 18 Nov 2025 11:29:38 +0100
Subject: [PATCH 17/27] * added asynchronous on_navigation_starting handler for
 Android * fixed too long lines * set asynchronous handler in example app

---
 android/src/toga_android/widgets/webview.py    | 18 ++++++++----------
 .../widgets/webview_static_proxy.py            | 15 ++++++++++++++-
 examples/webview/webview/app.py                |  4 ++--
 3 files changed, 24 insertions(+), 13 deletions(-)

diff --git a/android/src/toga_android/widgets/webview.py b/android/src/toga_android/widgets/webview.py
index d876c91263..13ce49143b 100644
--- a/android/src/toga_android/widgets/webview.py
+++ b/android/src/toga_android/widgets/webview.py
@@ -1,7 +1,6 @@
 import json
 from http.cookiejar import CookieJar
 
-
 from android.webkit import ValueCallback, WebView as A_WebView, WebViewClient
 from java import dynamic_proxy
 from java.lang import NoClassDefFoundError
@@ -27,6 +26,7 @@ def onReceiveValue(self, value):
 
 class WebView(Widget):
     SUPPORTS_ON_WEBVIEW_LOAD = False
+    SUPPORTS_ON_NAVIGATION_STARTING = True
 
     def create(self):
         self.native = A_WebView(self._native_activity)
@@ -35,16 +35,14 @@ def create(self):
 
             client = TogaWebClient(self)
         except NoClassDefFoundError:
+            self.SUPPORTS_ON_NAVIGATION_STARTING = False
             client = WebViewClient()
-            if self.interface.on_navigation_starting:
-                import sys
-                print(
-                    'chaquopy.defaultConfig.staticProxy'
-                    '("toga_android.widgets.webview_static_proxy") '
-                    'missing in pyproject.toml section "build_gradle_extra_content". '
-                    'on_navigation_starting handler is therefore not available',
-                    file=sys.stderr
-                )
+            print(
+                'chaquopy.defaultConfig.staticProxy("toga_android.widgets'
+                '.webview_static_proxy") missing in pyproject.toml section'
+                ' "build_gradle_extra_content". on_navigation_starting '
+                "handler is therefore not available"
+            )
         # Set a WebViewClient so that new links open in this activity,
         # rather than triggering the phone's web browser.
         self.native.setWebViewClient(client)
diff --git a/android/src/toga_android/widgets/webview_static_proxy.py b/android/src/toga_android/widgets/webview_static_proxy.py
index 85f9af10e8..d12e4ca667 100644
--- a/android/src/toga_android/widgets/webview_static_proxy.py
+++ b/android/src/toga_android/widgets/webview_static_proxy.py
@@ -1,3 +1,5 @@
+import asyncio
+
 from android.webkit import WebResourceRequest, WebView as A_WebView, WebViewClient
 from java import Override, jboolean, static_proxy
 
@@ -10,9 +12,20 @@ def __init__(self, impl):
     @Override(jboolean, [A_WebView, WebResourceRequest])
     def shouldOverrideUrlLoading(self, webview, webresourcerequest):
         if self.webview_impl.interface.on_navigation_starting:
-            allow = self.webview_impl.interface.on_navigation_starting(
+            result = self.webview_impl.interface.on_navigation_starting(
                 url=webresourcerequest.getUrl().toString()
             )
+            if isinstance(result, bool):
+                # on_navigation_starting handler is synchronous
+                allow = result
+            elif isinstance(result, asyncio.Future):
+                # on_navigation_starting handler is asynchronous
+                if result.done():
+                    allow = result.result()
+                else:
+                    # deny the navigation until the user himself or the user
+                    # defined on_navigation_starting handler has allowed it
+                    allow = False
             if not allow:
                 return True
         return False
diff --git a/examples/webview/webview/app.py b/examples/webview/webview/app.py
index 34f1ab05eb..66ab2a51c2 100644
--- a/examples/webview/webview/app.py
+++ b/examples/webview/webview/app.py
@@ -119,8 +119,8 @@ def startup(self):
             url="https://beeware.org/",
             on_webview_load=self.on_webview_load,
             flex=1,
-            # on_navigation_starting=self.on_navigation_starting_async,
-            on_navigation_starting=self.on_navigation_starting_sync,
+            on_navigation_starting=self.on_navigation_starting_async,
+            # on_navigation_starting=self.on_navigation_starting_sync,
         )
 
         box = toga.Box(

From 8d70393bcef00a096805eba9d2b46ae5894167c0 Mon Sep 17 00:00:00 2001
From: Tom Arn <sw@t-arn.com>
Date: Tue, 18 Nov 2025 11:50:21 +0100
Subject: [PATCH 18/27] fixed trailing blanks

---
 core/src/toga/widgets/webview.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/core/src/toga/widgets/webview.py b/core/src/toga/widgets/webview.py
index b1cb0ff22d..4d7f669a21 100644
--- a/core/src/toga/widgets/webview.py
+++ b/core/src/toga/widgets/webview.py
@@ -73,7 +73,7 @@ def __init__(
         super().__init__(id, style, **kwargs)
 
         self.user_agent = user_agent
-        
+
         # If URL is allowed by user interaction or user on_navigation_starting
         # handler, this attribute is True
         self._url_allowed = True

From 7862ff82c332722ed59f800ca0f50a17bc5d8026 Mon Sep 17 00:00:00 2001
From: Tom Arn <sw@t-arn.com>
Date: Tue, 18 Nov 2025 12:42:41 +0100
Subject: [PATCH 19/27] fixed tests for the added *args parameter passed to
 handler cleanup

---
 core/tests/test_handlers.py | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/core/tests/test_handlers.py b/core/tests/test_handlers.py
index 62bc8e2553..09aab8402e 100644
--- a/core/tests/test_handlers.py
+++ b/core/tests/test_handlers.py
@@ -148,7 +148,7 @@ def handler(*args, **kwargs):
     }
 
     # Cleanup method was invoked
-    cleanup.assert_called_once_with(obj, 42, kwarg1=3, kwarg2=4)
+    cleanup.assert_called_once_with(obj, 42, "arg1", "arg2", kwarg1=3, kwarg2=4)
 
 
 def test_function_handler_with_cleanup_error(capsys):
@@ -177,7 +177,7 @@ def handler(*args, **kwargs):
     }
 
     # Cleanup method was invoked
-    cleanup.assert_called_once_with(obj, 42, kwarg1=3, kwarg2=4)
+    cleanup.assert_called_once_with(obj, 42, "arg1", "arg2", kwarg1=3, kwarg2=4)
 
     # Evidence of the handler cleanup error is in the log.
     assert (
@@ -439,7 +439,7 @@ async def handler(*args, **kwargs):
     }
 
     # Cleanup method was invoked
-    cleanup.assert_called_once_with(obj, 42, kwarg1=3, kwarg2=4)
+    cleanup.assert_called_once_with(obj, 42, "arg1", "arg2", kwarg1=3, kwarg2=4)
 
 
 async def test_coroutine_handler_with_cleanup_error(capsys):
@@ -471,7 +471,7 @@ async def handler(*args, **kwargs):
     }
 
     # Cleanup method was invoked
-    cleanup.assert_called_once_with(obj, 42, kwarg1=3, kwarg2=4)
+    cleanup.assert_called_once_with(obj, 42, "arg1", "arg2", kwarg1=3, kwarg2=4)
 
     # Evidence of the handler cleanup error is in the log.
     assert (

From 82ebcf09a2dd21fcc837bac84551013446b86157 Mon Sep 17 00:00:00 2001
From: Tom Arn <sw@t-arn.com>
Date: Tue, 18 Nov 2025 14:08:18 +0100
Subject: [PATCH 20/27] * fixed call to handler cleanup * adjusted WebView
 documentation for Android's staticProxy * added Android staticProxy for
 testbed application * removed debugging prints

---
 android/src/toga_android/widgets/webview.py   | 4 ++--
 core/src/toga/handlers.py                     | 2 +-
 core/src/toga/widgets/webview.py              | 8 +++-----
 testbed/pyproject.toml                        | 2 ++
 winforms/src/toga_winforms/widgets/webview.py | 9 ++-------
 5 files changed, 10 insertions(+), 15 deletions(-)

diff --git a/android/src/toga_android/widgets/webview.py b/android/src/toga_android/widgets/webview.py
index 13ce49143b..15fe7849e4 100644
--- a/android/src/toga_android/widgets/webview.py
+++ b/android/src/toga_android/widgets/webview.py
@@ -39,8 +39,8 @@ def create(self):
             client = WebViewClient()
             print(
                 'chaquopy.defaultConfig.staticProxy("toga_android.widgets'
-                '.webview_static_proxy") missing in pyproject.toml section'
-                ' "build_gradle_extra_content". on_navigation_starting '
+                '.webview_static_proxy") missing in pyproject.toml section '
+                '"build_gradle_extra_content". on_navigation_starting '
                 "handler is therefore not available"
             )
         # Set a WebViewClient so that new links open in this activity,
diff --git a/core/src/toga/handlers.py b/core/src/toga/handlers.py
index 7e11eaecf2..070b8bbb1b 100644
--- a/core/src/toga/handlers.py
+++ b/core/src/toga/handlers.py
@@ -171,7 +171,7 @@ def _handler(*args: object, **kwargs: object) -> object:
                     else:
                         try:
                             if cleanup:
-                                cleanup(interface, result, **kwargs)
+                                cleanup(interface, result, *args, **kwargs)
                             return result
                         except Exception as e:
                             print("Error in handler cleanup:", e, file=sys.stderr)
diff --git a/core/src/toga/widgets/webview.py b/core/src/toga/widgets/webview.py
index 4d7f669a21..4e72033bbe 100644
--- a/core/src/toga/widgets/webview.py
+++ b/core/src/toga/widgets/webview.py
@@ -65,7 +65,9 @@ def __init__(
             web view is requesting permission to navigate or redirect
             to a different URI. The handler can be synchronous or async and must
             return True for allowing the URL, False for denying the URL or an awaited
-            QuestionDialog
+            QuestionDialog. On Android, this handler needs
+            `chaquopy.defaultConfig.staticProxy("toga_android.widgets.webview_static_proxy")`
+            in the build_gradle_extra_content section of pyproject.toml
         :param on_webview_load: A handler that will be invoked when the web view
             finishes loading.
         :param kwargs: Initial style properties.
@@ -151,14 +153,10 @@ def on_navigation_starting(self, handler):
         def cleanup(widget, result, **kwargs):
             url = kwargs.get("url", None)
             try:
-                msg = f"on_navigation_starting.cleanup, url={url}, "
-                msg += f"result={str(result)}"
-                print(msg)
                 if url is None:
                     # The user on_navigation_handler is synchronous - do nothing
                     return
                 if result is True:
-                    print(f"Navigating to {url}")
                     # navigate to the url, the URL will automatically be marked
                     # as allowed
                     self.url = url
diff --git a/testbed/pyproject.toml b/testbed/pyproject.toml
index 264525efc3..eb88f3932c 100644
--- a/testbed/pyproject.toml
+++ b/testbed/pyproject.toml
@@ -115,6 +115,8 @@ android.defaultConfig.python {
     // Pytest's assertion rewriting produces its own .pyc files.
     pyc.src = false
 }
+
+chaquopy.defaultConfig.staticProxy("toga_android.widgets.webview_static_proxy")
 """
 
 [tool.briefcase.app.testbed.web]
diff --git a/winforms/src/toga_winforms/widgets/webview.py b/winforms/src/toga_winforms/widgets/webview.py
index 1597dcd686..9c0e2c378e 100644
--- a/winforms/src/toga_winforms/widgets/webview.py
+++ b/winforms/src/toga_winforms/widgets/webview.py
@@ -184,12 +184,10 @@ def winforms_navigation_completed(self, sender, args):
             self.loaded_future = None
 
     def winforms_navigation_starting(self, sender, event):
-        print(f"winforms_navigation_starting: {event.Uri}")
         if self.interface.on_navigation_starting:
-            print("checking URL permission...")
+            # check URL permission
             if self.interface._url_allowed:
                 # URL is allowed by user code
-                print("URL is allowed by user code")
                 allow = True
                 # allow the URL only this time
                 self.interface._url_allowed = False
@@ -197,20 +195,17 @@ def winforms_navigation_starting(self, sender, event):
                 result = self.interface.on_navigation_starting(url=event.Uri)
                 if isinstance(result, bool):
                     # on_navigation_starting handler is synchronous
-                    print(f"synchronous handler, result={str(result)}")
                     allow = result
                 elif isinstance(result, asyncio.Future):
                     # on_navigation_starting handler is asynchronous
                     if result.done():
                         allow = result.result()
-                        print(f"asynchronous handler, result={str(allow)}")
                     else:
                         # deny the navigation until the user himself or the user
                         # defined on_navigation_starting handler has allowed it
                         allow = False
-                        print("waiting for permission")
             if not allow:
-                print("Denying navigation")
+                # Deny navigation
                 event.Cancel = True
 
     def get_url(self):

From ef4149df2a6ccf9c5bde57145924dabff5c4aa46 Mon Sep 17 00:00:00 2001
From: Tom Arn <sw@t-arn.com>
Date: Thu, 27 Nov 2025 00:37:19 +0100
Subject: [PATCH 21/27] added core tests

---
 core/tests/widgets/test_webview.py      | 84 +++++++++++++++++++++++++
 dummy/src/toga_dummy/widgets/webview.py | 26 ++++++++
 2 files changed, 110 insertions(+)

diff --git a/core/tests/widgets/test_webview.py b/core/tests/widgets/test_webview.py
index 951e133a1a..fa5200af15 100644
--- a/core/tests/widgets/test_webview.py
+++ b/core/tests/widgets/test_webview.py
@@ -34,12 +34,14 @@ def test_widget_created():
 def test_create_with_values():
     """A WebView can be created with initial values."""
     on_webview_load = Mock()
+    on_navigation_starting = Mock()
 
     widget = toga.WebView(
         id="foobar",
         url="https://beeware.org",
         user_agent="Custom agent",
         on_webview_load=on_webview_load,
+        on_navigation_starting=on_navigation_starting,
         # A style property
         width=256,
     )
@@ -50,6 +52,7 @@ def test_create_with_values():
     assert widget.url == "https://beeware.org"
     assert widget.user_agent == "Custom agent"
     assert widget.on_webview_load._raw == on_webview_load
+    assert widget.on_navigation_starting._raw == on_navigation_starting
     assert widget.style.width == 256
 
 
@@ -330,3 +333,84 @@ async def delayed_cookie_retrieval():
     assert cookie.path == "/"
     assert cookie.secure is True
     assert cookie.expires is None
+
+
+def test_webview_navigationstarting_disabled(monkeypatch):
+    """If the backend doesn't support on_navigation_starting, 
+    a warning is raised."""
+    try:
+        # Temporarily set the feature attribute on the backend
+        DummyWebView.SUPPORTS_ON_NAVIGATION_STARTING = False
+
+        # Instantiate a new widget with a hobbled backend.
+        widget = toga.WebView()
+        handler = Mock()
+
+        # Setting the handler raises a warning
+        with pytest.warns(
+            toga.NotImplementedWarning,
+            match=r"\[Dummy\] Not implemented: WebView\.on_navigation_starting",
+        ):
+            widget.on_navigation_starting = handler
+
+        # But the handler is still installed
+        assert widget.on_navigation_starting._raw == handler
+    finally:
+        # Clear the feature attribute.
+        del DummyWebView.SUPPORTS_ON_NAVIGATION_STARTING
+
+def test_navigation_starting_no_handler(widget):
+    """When no handler is set, navigation should be allowed"""
+
+    widget.url = None
+    widget._impl.simulate_navigation_starting("https://beeware.org")
+    assert widget.url == "https://beeware.org"
+
+def test_navigation_starting_sync(widget):
+    """Synchronous handler"""
+    def handler(widget, **kwargs):
+        url = kwargs.get("url", None)
+        if url == "https://beeware.org":
+            return True
+        else:
+            return False
+
+    widget.url = None
+    widget.on_navigation_starting = handler
+    # test allowed URL
+    widget._impl.simulate_navigation("https://beeware.org")
+    assert widget.url == "https://beeware.org"
+    # test denied URL
+    widget._impl.simulate_navigation("https://google.com")
+    assert widget.url == "https://beeware.org"
+
+async def test_navigation_starting_async(widget):
+    """ Mocking user response"""
+    async def dialog_mock(url):
+        await asyncio.sleep(0.3)
+        if url == "https://beeware.org":
+            return True
+        else:
+            return False
+
+    """Asynchronous handler"""
+    async def handler(widget, **kwargs):
+        url = kwargs.get("url", None)
+        return await dialog_mock(url)
+
+    widget.url = None
+    widget.on_navigation_starting = handler
+    # test allowed URL
+    widget._impl.simulate_navigation("https://beeware.org")
+    # navigation is denied until user decides
+    assert widget.url is None
+    # wait for the user response
+    asyncio.sleep(0.5)
+    assert widget.url == "https://beeware.org"
+    # test denied URL
+    widget._impl.simulate_navigation("https://google.com")
+    # navigation is denied until user decides
+    assert widget.url == "https://beeware.org"
+    # wait for the user response
+    asyncio.sleep(0.5)
+    assert widget.url == "https://beeware.org"
diff --git a/dummy/src/toga_dummy/widgets/webview.py b/dummy/src/toga_dummy/widgets/webview.py
index 4b6363aa07..677a9367b9 100644
--- a/dummy/src/toga_dummy/widgets/webview.py
+++ b/dummy/src/toga_dummy/widgets/webview.py
@@ -1,3 +1,4 @@
+import asyncio
 from http.cookiejar import CookieJar
 
 from toga.widgets.webview import CookiesResult, JavaScriptResult
@@ -53,3 +54,28 @@ def simulate_cookie_retrieval(self, cookies):
         for cookie in cookies:
             cookie_jar.set_cookie(cookie)
         self._cookie_result.set_result(cookie_jar)
+
+    def simulate_navigation_starting(self, url):
+        """Simulate a navigation"""
+        allow = True
+        if self.interface.on_navigation_starting:
+            if self.interface._url_allowed:
+                # URL is allowed by user code
+                allow = True
+                # allow the URL only this time
+                self.interface._url_allowed = False
+            else:
+                result = self.interface.on_navigation_starting(url=url)
+                if isinstance(result, bool):
+                    # on_navigation_starting handler is synchronous
+                    allow = result
+                elif isinstance(result, asyncio.Future):
+                    # on_navigation_starting handler is asynchronous
+                    if result.done():
+                        allow = result.result()
+                    else:
+                        # deny the navigation until the user himself or the user
+                        # defined on_navigation_starting handler has allowed it
+                        allow = False
+        if allow:
+            self.set_url(url)

From d6f9ab532551b24a48e81f2a0cda216b68136be3 Mon Sep 17 00:00:00 2001
From: Tom Arn <sw@t-arn.com>
Date: Thu, 27 Nov 2025 06:40:53 +0100
Subject: [PATCH 22/27] * fixing pre-commit failures

---
 core/tests/widgets/test_webview.py                    | 10 ++++++++--
 positron/src/positron/django_templates/manage.py.tmpl |  1 +
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/core/tests/widgets/test_webview.py b/core/tests/widgets/test_webview.py
index fa5200af15..a064bb8d91 100644
--- a/core/tests/widgets/test_webview.py
+++ b/core/tests/widgets/test_webview.py
@@ -336,7 +336,7 @@ async def delayed_cookie_retrieval():
 
 
 def test_webview_navigationstarting_disabled(monkeypatch):
-    """If the backend doesn't support on_navigation_starting, 
+    """If the backend doesn't support on_navigation_starting,
     a warning is raised."""
     try:
         # Temporarily set the feature attribute on the backend
@@ -359,6 +359,7 @@ def test_webview_navigationstarting_disabled(monkeypatch):
         # Clear the feature attribute.
         del DummyWebView.SUPPORTS_ON_NAVIGATION_STARTING
 
+
 def test_navigation_starting_no_handler(widget):
     """When no handler is set, navigation should be allowed"""
 
@@ -366,8 +367,10 @@ def test_navigation_starting_no_handler(widget):
     widget._impl.simulate_navigation_starting("https://beeware.org")
     assert widget.url == "https://beeware.org"
 
+
 def test_navigation_starting_sync(widget):
     """Synchronous handler"""
+
     def handler(widget, **kwargs):
         url = kwargs.get("url", None)
         if url == "https://beeware.org":
@@ -384,8 +387,10 @@ def handler(widget, **kwargs):
     widget._impl.simulate_navigation("https://google.com")
     assert widget.url == "https://beeware.org"
 
+
 async def test_navigation_starting_async(widget):
-    """ Mocking user response"""
+    """Mocking user response"""
+
     async def dialog_mock(url):
         await asyncio.sleep(0.3)
         if url == "https://beeware.org":
@@ -394,6 +399,7 @@ async def dialog_mock(url):
             return False
 
     """Asynchronous handler"""
+
     async def handler(widget, **kwargs):
         url = kwargs.get("url", None)
         return await dialog_mock(url)
diff --git a/positron/src/positron/django_templates/manage.py.tmpl b/positron/src/positron/django_templates/manage.py.tmpl
index 9a95520e2d..137db483d7 100644
--- a/positron/src/positron/django_templates/manage.py.tmpl
+++ b/positron/src/positron/django_templates/manage.py.tmpl
@@ -1,5 +1,6 @@
 #!/usr/bin/env python
 """Django's command-line utility for administrative tasks."""
+
 import os
 import sys
 

From 1cb8fbf2a1c9e98b3b8c30ff1c60edece7c7a110 Mon Sep 17 00:00:00 2001
From: Tom Arn <sw@t-arn.com>
Date: Thu, 27 Nov 2025 08:04:55 +0100
Subject: [PATCH 23/27] * fixed test_webview_navigationstarting_disabled *
 fixed test_navigation_starting_async

---
 core/tests/widgets/test_webview.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/core/tests/widgets/test_webview.py b/core/tests/widgets/test_webview.py
index a064bb8d91..cbf396538c 100644
--- a/core/tests/widgets/test_webview.py
+++ b/core/tests/widgets/test_webview.py
@@ -353,8 +353,8 @@ def test_webview_navigationstarting_disabled(monkeypatch):
         ):
             widget.on_navigation_starting = handler
 
-        # But the handler is still installed
-        assert widget.on_navigation_starting._raw == handler
+        # The handler is not installed
+        assert widget.on_navigation_starting is None
     finally:
         # Clear the feature attribute.
         del DummyWebView.SUPPORTS_ON_NAVIGATION_STARTING
@@ -405,6 +405,7 @@ async def handler(widget, **kwargs):
         return await dialog_mock(url)
 
     widget.url = None
+    self.interface._url_allowed = False
     widget.on_navigation_starting = handler
     # test allowed URL
     widget._impl.simulate_navigation("https://beeware.org")

From 7444b1a7426471db2498373ec7aaef65951df677 Mon Sep 17 00:00:00 2001
From: Tom Arn <sw@t-arn.com>
Date: Thu, 27 Nov 2025 08:31:19 +0100
Subject: [PATCH 24/27] fixed test_navigation_starting_async

---
 core/tests/widgets/test_webview.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/core/tests/widgets/test_webview.py b/core/tests/widgets/test_webview.py
index cbf396538c..03b0bcfc06 100644
--- a/core/tests/widgets/test_webview.py
+++ b/core/tests/widgets/test_webview.py
@@ -405,7 +405,7 @@ async def handler(widget, **kwargs):
         return await dialog_mock(url)
 
     widget.url = None
-    self.interface._url_allowed = False
+    widget._url_allowed = False
     widget.on_navigation_starting = handler
     # test allowed URL
     widget._impl.simulate_navigation("https://beeware.org")

From 48e9af8a01cc9d6d9824a774e58957f576962ab7 Mon Sep 17 00:00:00 2001
From: Tom Arn <sw@t-arn.com>
Date: Thu, 27 Nov 2025 08:58:45 +0100
Subject: [PATCH 25/27] fixed test_webview.py

---
 core/tests/widgets/test_webview.py | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/core/tests/widgets/test_webview.py b/core/tests/widgets/test_webview.py
index 03b0bcfc06..e02a15abaf 100644
--- a/core/tests/widgets/test_webview.py
+++ b/core/tests/widgets/test_webview.py
@@ -381,10 +381,10 @@ def handler(widget, **kwargs):
     widget.url = None
     widget.on_navigation_starting = handler
     # test allowed URL
-    widget._impl.simulate_navigation("https://beeware.org")
+    widget._impl.simulate_navigation_starting("https://beeware.org")
     assert widget.url == "https://beeware.org"
     # test denied URL
-    widget._impl.simulate_navigation("https://google.com")
+    widget._impl.simulate_navigation_starting("https://google.com")
     assert widget.url == "https://beeware.org"
 
 
@@ -408,14 +408,14 @@ async def handler(widget, **kwargs):
     widget._url_allowed = False
     widget.on_navigation_starting = handler
     # test allowed URL
-    widget._impl.simulate_navigation("https://beeware.org")
+    widget._impl.simulate_navigation_starting("https://beeware.org")
     # navigation is denied until user decides
     assert widget.url is None
     # wait for the user response
     asyncio.sleep(0.5)
     assert widget.url == "https://beeware.org"
     # test denied URL
-    widget._impl.simulate_navigation("https://google.com")
+    widget._impl.simulate_navigation_starting("https://google.com")
     # navigation is denied until user decides
     assert widget.url == "https://beeware.org"
     # wait for the user response

From 5773f037be6117516d97d132a3fbbaef32e0cd23 Mon Sep 17 00:00:00 2001
From: Tom Arn <sw@t-arn.com>
Date: Thu, 27 Nov 2025 09:13:22 +0100
Subject: [PATCH 26/27] fixed test_webview.py

---
 core/tests/widgets/test_webview.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/core/tests/widgets/test_webview.py b/core/tests/widgets/test_webview.py
index e02a15abaf..721cb6a45a 100644
--- a/core/tests/widgets/test_webview.py
+++ b/core/tests/widgets/test_webview.py
@@ -412,12 +412,12 @@ async def handler(widget, **kwargs):
     # navigation is denied until user decides
     assert widget.url is None
     # wait for the user response
-    asyncio.sleep(0.5)
+    await asyncio.sleep(0.5)
     assert widget.url == "https://beeware.org"
     # test denied URL
     widget._impl.simulate_navigation_starting("https://google.com")
     # navigation is denied until user decides
     assert widget.url == "https://beeware.org"
     # wait for the user response
-    asyncio.sleep(0.5)
+    await asyncio.sleep(0.5)
     assert widget.url == "https://beeware.org"

From b7a622199964eb43dc7a5f10680543434844f216 Mon Sep 17 00:00:00 2001
From: Tom Arn <sw@t-arn.com>
Date: Fri, 28 Nov 2025 13:03:08 +0100
Subject: [PATCH 27/27] * added test for None URL * added test for set_content
 with navigation_starting handler * removed unnecessary try block * modified
 set_url on dummy platform

---
 core/src/toga/widgets/webview.py        | 17 +++++++----------
 core/tests/widgets/test_webview.py      | 18 ++++++++++++++++++
 dummy/src/toga_dummy/widgets/webview.py |  2 ++
 ~toxtest.cmd                            |  1 +
 4 files changed, 28 insertions(+), 10 deletions(-)
 create mode 100644 ~toxtest.cmd

diff --git a/core/src/toga/widgets/webview.py b/core/src/toga/widgets/webview.py
index 4e72033bbe..8350e22a63 100644
--- a/core/src/toga/widgets/webview.py
+++ b/core/src/toga/widgets/webview.py
@@ -152,16 +152,13 @@ def on_navigation_starting(self, handler):
 
         def cleanup(widget, result, **kwargs):
             url = kwargs.get("url", None)
-            try:
-                if url is None:
-                    # The user on_navigation_handler is synchronous - do nothing
-                    return
-                if result is True:
-                    # navigate to the url, the URL will automatically be marked
-                    # as allowed
-                    self.url = url
-            except Exception as ex:
-                print(f"on_navigation_starting.cleanup exception: {str(ex)}")
+            if url is None:
+                # The user on_navigation_handler is synchronous - do nothing
+                return
+            if result is True:
+                # navigate to the url, the URL will automatically be marked
+                # as allowed
+                self.url = url
 
         self._on_navigation_starting = None
         if handler:
diff --git a/core/tests/widgets/test_webview.py b/core/tests/widgets/test_webview.py
index 721cb6a45a..e4cea1cfb0 100644
--- a/core/tests/widgets/test_webview.py
+++ b/core/tests/widgets/test_webview.py
@@ -209,6 +209,21 @@ def test_set_content_with_property(widget):
     )
 
 
+def test_set_content_with_navigation_starting(widget):
+    """Static HTML content can be loaded into the page, using a setter."""
+    # Set up a navigation_starting handler
+    handler = Mock()
+    widget.on_navigation_starting = handler
+    # Set the content
+    widget.content = "<h1>Fancy page</h1>"
+    assert_action_performed_with(
+        widget,
+        "set content",
+        root_url="",
+        content="<h1>Fancy page</h1>",
+    )
+
+
 def test_get_content_property_error(widget):
     """Verify that using the getter on widget.content fails."""
     with pytest.raises(AttributeError):
@@ -380,6 +395,9 @@ def handler(widget, **kwargs):
 
     widget.url = None
     widget.on_navigation_starting = handler
+    # test None-URL
+    widget._impl.simulate_navigation_starting(None)
+    assert widget.url is None
     # test allowed URL
     widget._impl.simulate_navigation_starting("https://beeware.org")
     assert widget.url == "https://beeware.org"
diff --git a/dummy/src/toga_dummy/widgets/webview.py b/dummy/src/toga_dummy/widgets/webview.py
index 677a9367b9..b2ec198692 100644
--- a/dummy/src/toga_dummy/widgets/webview.py
+++ b/dummy/src/toga_dummy/widgets/webview.py
@@ -26,6 +26,8 @@ def get_url(self):
     def set_url(self, value, future=None):
         self._set_value("url", value)
         self._set_value("loaded_future", future)
+        # allow the URL only once
+        self.interface._url_allowed = False
 
     def get_cookies(self):
         self._action("cookies")
diff --git a/~toxtest.cmd b/~toxtest.cmd
new file mode 100644
index 0000000000..7789eb0def
--- /dev/null
+++ b/~toxtest.cmd
@@ -0,0 +1 @@
+tox -e py -- tests/widgets/test_webview.py