[WinUI][dotnet8] - New window blinks when loading a content.

[rodirigos]

Describe the bug

In .NET 7, windows wait to render the content before opening. In .NET 8 and later, an unintended flicker occurs while loading this content. This flicker comes with a default background. It also occurs using MAUI.

Steps to reproduce the bug

1 - Create multiple windows with some content and an alternative background color.

Expected behavior

It should open like in dotnet7, appearing all the window with a rendered content. (not a flickering before opening).

Screenshots

NuGet package version

None

Windows version

No response

Additional context

No response

[danielancines]

I have a MDI large application for a Bank in .net Maui, using Pinvoke.SetParent and not able to migrate to .net 8 and 9 because of this behavior.

[lfmouradasilva]

Same issue here. This is a breaking change, and it’s blocking me from updating my application.

[fpedrolucas95]

I'm also experiencing this flickering issue in a .NET Maui desktop application. This is a significant blocker for updating to .NET 8 and 9, as it creates a poor user experience.

[Elwilton]

I’m facing the same issue. I’m trying to migrate from .NET 7 to .NET 8 and having problems with the presentation of new screens.

[lgztx96]

Similar problems exist when using the C++ language.

[MasterOliver21]

I encountered the same problem in some tests I did while migrating the .NET version. Because of that, I had to pause the migration.

[rodirigos]

Here's some example using WinUI
https://github.com/rodirigos/NewWindowTest
There's already an example in Maui with a more appealing issue

[lhak]

@rodirigos You can set the RequestedTheme property of the StackPanel (the window content) to ElementTheme.Dark if you want the window background color to be black.

[danielancines]

@rodirigos You can set the RequestedTheme property of the StackPanel (the window content) to ElementTheme.Dark if you want the window background color to be black.

Yes, the window background was black and behavior is the same, but less visible.

[rodirigos]

@rodirigos You can set the RequestedTheme property of the StackPanel (the window content) to ElementTheme.Dark if you want the window background color to be black.

Same behavior. Only changed the color to show the delay. As you can see in the example above, the labels inside the content still have the same issue.

[castorix]

@rodirigos You can set the RequestedTheme property of the StackPanel (the window content) to ElementTheme.Dark if you want the window background color to be black.

Same behavior. Only changed the color to show the delay. As you can see in the example above, the labels inside the content still have the same issue.

I have the same problem in .NET 7.0 (Windows 10 22H2, Windows App SDK 1.6.241114003, slow PC)
Test with your sample (I just changed colors, size, ...) :

[lhak]

One issue here is that all windows are created and shown on the UI thread, so there is never a chance for the content to render until all windows are visible. Moving the call of window.Activate() to a low priority dispatcher call with DispatcherQueue.TryEnqueue might improve things.

However, in my experience, some delay between the window background and the XAML content showing cannot currently be avoided. I guess a fix would require more work in winui to pre-render the content before the window is visible.