Accessing NonClientRegionsChangedEventArgs.ChangedRegions with AOT enabled causes NotSupportedException

[SuGar0218]

Describe the bug

When NativeAOT is enabled, accessing NonClientRegionsChangedEventArgs.ChangedRegions in my InputNonClientPointerSource.RegionsChanged event handler, it throws System.NotSupportedException with message "Cannot handle array marshalling for non blittable type 'Microsoft.UI.Input.NonClientRegionKind'.". But it works properly without NativeAOT.

Why is this important?

• Non-client regions set by InputNonClientPointerSource.SetRegionRects will become 0×0 rects unexpectedly, for example, when the title bar area set by Window.SetTitleBar and InputNonClientPointerSource.SetRegionRects with NonClientKind.Caption dragged and clicked. It is also mentioned at Setting the maximize region of a win32 window using InputNonClientPointerSource secretly reverts back to default #10379 . Handling InputNonClientPointerSource.RegionsChanged event is a feasible way to remedy this issue.
• NativeAOT is a good feature.

Steps to reproduce the bug

1. Create a new C# WinUI 3 project.
2. Enable "Publish Native AOT" in the project property settings.
3. Handle InputNonClientPointerSource.RegionsChanged event and access NonClientRegionsChangedEventArgs.ChangedRegions.

public sealed partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
        ExtendsContentIntoTitleBar = true;
        _inputNonClientPointerSource = InputNonClientPointerSource.GetForWindowId(AppWindow.Id);
        _inputNonClientPointerSource.RegionsChanged += OnNonClientRegionsChanged;
    }

    private void OnNonClientRegionsChanged(InputNonClientPointerSource sender, NonClientRegionsChangedEventArgs args)
    {
        NonClientRegionKind[] changedRegions = args.ChangedRegions;
    }

    private readonly InputNonClientPointerSource _inputNonClientPointerSource;
}

Actual behavior

System.NotSupportedException is thrown at NonClientRegionKind[] changedRegions = args.ChangedRegions with message: "Cannot handle array marshalling for non blittable type 'Microsoft.UI.Input.NonClientRegionKind'".

Expected behavior

Cause no exceptions.

Screenshots

NuGet package version

WinUI 3 - Windows App SDK 1.8.1: 1.8.250916003

Windows version

Windows 11 (24H2): Build 26100

Additional context

No response

[snigdha011997]

Hi @SuGar0218 , can you help us by providing minimal repro project?

[SuGar0218]

Hi @SuGar0218 , can you help us by providing minimal repro project?

https://github.com/SuGar0218/MicrosoftUIXamlIssue10835

[manodasanW]

Hey @SuGar0218, support for marshaling non-blittable array is currently available in the Microsoft.Windows.CsWinRT previews when you are targeting .NET 9 or later. So, if you update your project to have a package reference to the CsWinRT preview package and update your target framework to .NET 9 or later, you should see this issue go away.