[Windows] Fix runtime theme update for controls and TitleBar

[Tamilarasan-Paranthaman]

Note

Are you waiting for the changes in this PR to be merged?
It would be very helpful if you could test the resulting artifacts from this PR and let us know in a comment if this change resolves your issue. Thank you!

Root Cause of the Issue:

• In WinUI, the theme can only be set when the app is started, not while it's running. On the .NET MAUI side, we explicitly update control colors according to the defined styles for the respective theme. As a result, colors were updated correctly for the controls we handled explicitly.

• However, controls where we did not explicitly set the colors (e.g., DatePicker/TimePicker backgrounds, Checkbox tick marks, and TitleBar colors) were not updated properly when the theme changed.

• This happens because WinUI default colors are tied to the theme at the time the app is launched. For example, if the app starts in Light theme, the WinUI theme is initialized as Light and its colors are applied for the entire lifecycle. These defaults are not refreshed when the theme changes at runtime.

• Due to this limitation, theme-related colors (including TitleBar color) were not updated as expected.

Description of Change

• Implemented a common logic to apply the appropriate theme by setting the RequestedTheme on the root view of the Window. This approach is consistent with what is used in the WinUI Gallery repo.

• With this change, theme-related colors are correctly refreshed across all child views, resolving both theming inconsistencies and the TitleBar color issue when the app theme is changed.

Reference:

• The implementation is based on the following references. Additionally, there is a known issue in WinUI where updating the theme at runtime does not refresh the TitleBar caption button colors, which requires manual handling.

• Updating Root View RequestedTheme: https://github.com/microsoft/WinUI-Gallery/blob/96dc185a3a3e488f820d06579d85cb4f480a7089/WinUIGallery/Helpers/ThemeHelper.cs#L62

• AppWindow TitleBar doesn't update caption button colors correctly when changed while app is running: https://github.com/microsoft/WinUI-Gallery/blob/96dc185a3a3e488f820d06579d85cb4f480a7089/WinUIGallery/Helpers/TitleBarHelper.cs#L22

Screenshot

Before Fix	After Fix
Before-Fix.mp4	After-Fix.mp4

Issues Fixed

Fixes #12507
Fixes #22058
Fixes #30518 (Windows)
Fixes #30807
Fixes #31819

[Copilot]

Pull Request Overview

This PR fixes runtime theme changes for Windows controls and TitleBar by implementing proper theme propagation through WinUI's root view element. The issue occurred because WinUI's default colors are tied to the theme at app launch and don't update when the theme changes at runtime.

• Implements theme application by setting RequestedTheme on the root view of each window
• Adds proper TitleBar button color handling for theme changes
• Creates comprehensive UI tests to validate theme switching behavior

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/Core/src/Platform/Windows/MauiWinUIWindow.cs	Removes hardcoded theme logic and adds code style improvements
src/Controls/src/Core/Application/Application.cs	Adds platform-specific hooks for theme and window lifecycle events
src/Controls/src/Core/Application/Application.Windows.cs	Implements Windows-specific theme application logic and TitleBar color management
src/Controls/tests/TestCases.HostApp/Issues/Issue22058.cs	Creates test UI page with theme switching button and TimePicker
src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue22058.cs	Adds automated test to verify theme changes work correctly

[malsabi]

Does this work also on Picker control it uses ComboBox for WinUI, I faced issues with the drop-down menu and context-menu's not respecting the theme light / dark mode. Can you please confirm. @Tamilarasan-Paranthaman

[Tamilarasan-Paranthaman]

Does this work also on Picker control it uses ComboBox for WinUI, I faced issues with the drop-down menu and context-menu's not respecting the theme light / dark mode. Can you please confirm. @Tamilarasan-Paranthaman

@malsabi, yes, I have tested this with the Picker control, and it respects Light/Dark theme changes correctly with this fix. I have attached the test code along with videos showing the behavior both with the latest NuGet version and with this fix for your reference. Please let me know if there are any other scenarios you would like me to check, and I will check them on my end and update you.

Tested Code:

<Picker x:Name="picker"
      VerticalOptions="Center"
      Title="Select a monkey">
  <Picker.ItemsSource>
    <x:Array Type="{x:Type x:String}">
      <x:String>Baboon</x:String>
      <x:String>Capuchin Monkey</x:String>
      <x:String>Blue Monkey</x:String>
      <x:String>Squirrel Monkey</x:String>
      <x:String>Golden Lion Tamarin</x:String>
      <x:String>Howler Monkey</x:String>
      <x:String>Japanese Macaque</x:String>
    </x:Array>
  </Picker.ItemsSource>
</Picker>

Screenshot

With latest NuGet	With this Fix
Picker-With-Latest-NuGet.mp4	Picker-With-This-Fix.mp4

[jsuarezruiz]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[jsuarezruiz]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[Tamilarasan-Paranthaman]

@jsuarezruiz, it seems the CI generated images are not rendered properly on Windows. The Title Bar is not visible, and a grey overlay appears in the images.

However, the sample works as expected when run locally. I have attached the CI generated images below for your reference.

I also added a Thread.Sleep after the theme change, maybe that isn’t the proper approach? Should we use Task.Delay instead? I’m not sure why it behaves differently in the CI environment.

I have now replaced Thread.Sleep with Task.Delay. Could you please run the UI tests to regenerate the Windows images?

Debugging in local	CI Images (Windows)
App.mp4

[jsuarezruiz]

/azp run MAUI-UITests-public

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[Tamilarasan-Paranthaman]

@jsuarezruiz, The image is still not generated properly, and this issue occurs only in the CI environment. When I debug the sample locally, it works fine. It also works correctly when I run it from the Test Explorer in Visual Studio. For now, I have added the CI generated image and also set the page’s BackgroundProperty using SetAppThemeColor to see if it helps in the CI environment. Could you please share your insights on this?

[PureWeen]

/azp run maui-pr-uitests, maui-pr-devicetests

[azure-pipelines]

Azure Pipelines successfully started running 2 pipeline(s).