fix(win32): remove WS_VISIBLE and add assert in GetClientArea

windows/runner/win32_window.cpp

@@ -1,5 +1,6 @@
 #include "win32_window.h"
 
+#include <cassert>
 #include <dwmapi.h>
 #include <flutter_windows.h>
 
@@ -134,6 +135,7 @@ bool Win32Window::Create(const std::wstring& title,
   UINT dpi = FlutterDesktopGetDpiForMonitor(monitor);
   double scale_factor = dpi / 96.0;
 
+  // Create window WITHOUT WS_VISIBLE flag - visibility controlled by Show()
   HWND window = CreateWindow(
       window_class, title.c_str(), WS_OVERLAPPEDWINDOW,
       Scale(origin.x, scale_factor), Scale(origin.y, scale_factor),
@@ -144,12 +146,24 @@ bool Win32Window::Create(const std::wstring& title,
     return false;
   }
 
+  // Set window_handle_ immediately after CreateWindow returns
+  window_handle_ = window;
+
+  // Do NOT call ShowWindow here - let the caller control visibility via Show()
+  // Do NOT call UpdateWindow here - window is not visible yet
+
   UpdateTheme(window);
 
   return OnCreate();
 }
 
 bool Win32Window::Show() {
+  // Show requires a valid window handle
+  assert(window_handle_ && "Show() called before window was created");
+
+  if (!window_handle_) {
+    return false;
+  }
   return ShowWindow(window_handle_, SW_SHOWNORMAL);
 }
 
@@ -164,8 +178,11 @@ LRESULT CALLBACK Win32Window::WndProc(HWND const window,
                      reinterpret_cast<LONG_PTR>(window_struct->lpCreateParams));
 
     auto that = static_cast<Win32Window*>(window_struct->lpCreateParams);
+    // Ensure window_handle_ is set (it should already be set in Create())
+    if (!that->window_handle_) {
+      that->window_handle_ = window;
+    }
     EnableFullDpiSupportIfAvailable(window);
-    that->window_handle_ = window;
   } else if (Win32Window* that = GetThisFromHandle(window)) {
     return that->MessageHandler(window, message, wparam, lparam);
   }
@@ -239,6 +256,13 @@ Win32Window* Win32Window::GetThisFromHandle(HWND const window) noexcept {
 }
 
 void Win32Window::SetChildContent(HWND content) {
+  // SetChildContent requires a valid window handle
+  assert(window_handle_ && "SetChildContent() called before window was created");
+
+  if (!window_handle_) {
+    return;
+  }
+
   child_content_ = content;
   SetParent(content, window_handle_);
   RECT frame = GetClientArea();
@@ -250,8 +274,16 @@ void Win32Window::SetChildContent(HWND content) {
 }
 
 RECT Win32Window::GetClientArea() {
-  RECT frame;
-  GetClientRect(window_handle_, &frame);
+  // GetClientArea assumes that window_handle_ has been created and is valid.
+  // A null window_handle_ indicates a usage error at the call site.
+  RECT frame{0, 0, 0, 0};
+
+  assert(window_handle_ && "GetClientArea called with null window_handle_");
+
+  if (window_handle_) {
+    GetClientRect(window_handle_, &frame);
+  }
+
   return frame;
 }
 
@@ -273,6 +305,10 @@ void Win32Window::OnDestroy() {
 }
 
 void Win32Window::UpdateTheme(HWND const window) {
+  if (!window) {
+    return;
+  }
+
   DWORD light_mode;
   DWORD light_mode_size = sizeof(light_mode);
   LSTATUS result = RegGetValue(HKEY_CURRENT_USER, kGetPreferredBrightnessRegKey,
@@ -282,7 +318,11 @@ void Win32Window::UpdateTheme(HWND const window) {
 
   if (result == ERROR_SUCCESS) {
     BOOL enable_dark_mode = light_mode == 0;
-    DwmSetWindowAttribute(window, DWMWA_USE_IMMERSIVE_DARK_MODE,
-                          &enable_dark_mode, sizeof(enable_dark_mode));
+    // Try to set dark mode attribute - will fail silently on unsupported Windows versions
+    HRESULT hr = DwmSetWindowAttribute(window, DWMWA_USE_IMMERSIVE_DARK_MODE,
+                                      &enable_dark_mode, sizeof(enable_dark_mode));
+    // hr will be E_INVALIDARG (0x80070057) on Windows versions < 10.0.17763
+    // We ignore the error as dark mode is not supported on older versions
+    (void)hr; // Suppress unused variable warning
   }
-}
+}