[Misaka-L]

What does the pull request do?

This pull request will call Screen?.OnChanged() when received window message WM_SETTINGCHANGE with wParam SPI_SETWORKAREA.

What is the current behavior?

Screens.Changed won't trigger and screen WorkingArea property won't updated if only working area changed.
(Change taskbar position or size will change the working area)

What is the updated/expected behavior with this PR?

Screens.Changed will trigger and screen WorkingArea property will also update if working area changed.

How was the solution implemented (if it's not obvious)?

This pull request add a case for WM_SETTINGCHANGE in AppWndProc, which will call Screen?.OnChanged(), update the screen working area property and trigger Screens.Changed.

Test Video

See WorkingArea and Screens.Changed Trigger Counter

2026-07-05.23-31-44.mp4

Checklist

• Added unit tests (if possible)?
  • Currently no way to trigger working area changed without modify OS settings.
  • Update the IntergrationTestApp to test this patch. See above.
• Added XML documentation to any related classes?
• Consider submitting a PR to https://github.com/AvaloniaUI/avalonia-docs with user documentation

Fixed issues

Fixes #19006

[avaloniaui-bot]

You can test this PR using the following package version. 12.1.999-cibuild0067169-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[avaloniaui-bot]

You can test this PR using the following package version. 12.1.999-cibuild0067191-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[MrJul]

Don't do this in the window-specific wndproc. Use Win32Platform.WndProc instead, which is meant for "global" messages.

[Misaka-L]

Logic move to existing WindowsMessage.WM_SETTINGCHANGE if statement in Win32Platform.WndProc.

Avalonia/src/Windows/Avalonia.Win32/Win32Platform.cs

Lines 178 to 195 in 8193052

	if (msg == (uint)WindowsMessage.WM_SETTINGCHANGE
	&& PlatformSettings is Win32PlatformSettings win32PlatformSettings)
	{
	var changedSetting = Marshal.PtrToStringAuto(lParam);
	if (changedSetting == "ImmersiveColorSet" // dark/light mode
	|| changedSetting == "WindowsThemeElement") // high contrast mode
	{
	win32PlatformSettings.OnColorValuesChanged();
	}
	// Notify WorkingArea changed to Screens
	if ((SystemParametersInfo)wParam == SystemParametersInfo.SPI_SETWORKAREA)
	{
	Screen?.OnChanged();
	}
	}

[Misaka-L]

I just notice that this statement will only run if PlatformSettings is Win32PlatformSettings win32PlatformSettings...
Should I make a new if statement for this patch?

[MrJul]

Keep a single if (msg == (uint)WindowsMessage.WM_SETTINGCHANGE) for both but wrap the existing color change with an inner if (PlatformSettings is Win32PlatformSettings win32PlatformSettings)

[Misaka-L]

Patched

[avaloniaui-bot]

You can test this PR using the following package version. 12.1.999-cibuild0067207-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[MrJul]

Works as advertised.
LGTM!