XAML Islands - Empty DesktopWindowXamlSource window visible on task bar

[taenri]

Describe the bug

When running a XAML Islands Win32 Desktop app using Win UI 2.6.1 Preview, a blank window with title DesktopWindowXamlSource appears on the task bar.

When the user opens a valid XAML Islands window, the content for DesktopWindowXamlSource is set and it is attached to an HWND. At this point the 'blank' DesktopWindowXamlSource window disappears. As soon as the user closes the XAML Islands window, however, the blank DesktopWindowXamlSource window reappears.

Also notable: closing this blank window will also cause the entire process to exit.

Our app usually does not show any window until the user explicitly opens one through a systray icon, so most of the time the content for DesktopWindowXamlSource is expected to be empty and its HWND should be invisible to the user.

We have found that this issue only repros in the Windows 10 Insider build 19044.1348.

I have also confirmed that this issue persists in Win UI 2.8.0 Preview.

Steps to reproduce the bug

I was able to repro the issue using the xaml-islands Playground found in this repo: https://github.com/asklar/xaml-islands/tree/main/Playground

1. Clone the xaml-islands repo above.
2. Comment out lines 172-251 in Playground\WindowsProject1.cpp to ensure that the DesktopWindowXamlSource hwnd content does not get set on startup.
3. Build the Playground solution and launch the executable in Windows 10 build 19044 (I can help validate changes on this build of windows if needed)
4. Observe that an empty DesktopWindowXamlSource window appears in the task bar.

Expected behavior

When using XAML Islands with WinUI 2X preview, the blank DesktopWindowXamlSource HWND should not be visible at all to the user when it is not actively hosting any content.

Screenshots

NuGet package versions

Microsoft.UI.Xaml.2.6.1-prerelease.210709001
Microsoft.UI.Xaml.2.7.0-prerelease.210913003
Microsoft.UI.Xaml.2.8.0-prerelease.210927001

Windows app type

• UWP
• Win32

Device form factor

Desktop

Windows version

Insider Build (19044)

Additional context

No response

[zadjii-msft]

Possibly relevant discussion: microsoft/terminal#6507 (comment)

[sylveon]

This is the fake CoreWindow used for OS XAML compat. What I do is grab the HWND of the window using

HWND hwnd;
winrt::check_hresult(winrt::Windows::UI::Core::CoreWindow::GetForCurrentThread().as<ICoreWindowInterop>()->get_WindowHandle(&hwnd));

Then I can just call ShowWindow(hwnd, SW_HIDE);

[sylveon]

@MattTheTechLV this issue is for bugs with the XAML Islands API, not end user applications.

[sylveon]

@MattTheTechLV this issue is for bugs with the XAML Islands API, not end user applications.

[MattTheTechLV]

@MattTheTechLV this issue is for bugs with the XAML Islands API, not end user applications.

Yup sorry, I was directed by a Contributor where I originally posted saying it belonged here, then realized right after I posted it, that it in fact did not belong here, and I had posted in the correct place originally. So I deleted my comment almost right away. Sorry about the confusion.

[taenri]

This is the fake CoreWindow used for OS XAML compat. What I do is grab the HWND of the window using

HWND hwnd;
winrt::check_hresult(winrt::Windows::UI::Core::CoreWindow::GetForCurrentThread().as<ICoreWindowInterop>()->get_WindowHandle(&hwnd));

Then I can just call ShowWindow(hwnd, SW_HIDE);

@sylveon - We are performing similar logic by using EnumThreadWindows to search for window handles created on our main thread with the title of "DesktopWindowXamlSource". Then we are calling ShowWindow(hwnd, SW_HIDE) to manually hide it. This seems to work well in our local testing using a virtual machine with the same version of Windows 10 that we know to be affected (build 19044, aka 21H2). On my VM, the issue persists without this manual hiding logic but fixed when our manual hiding logic is applied.

However, many of our users are still reporting this issue despite our best efforts. My understanding is that this bug has been fixed at the OS-level within the CoreWindow object itself in Windows 11 (from within the Windows.UI.Core namespace) but has not been patched for Windows 10.

[mario-beeler]

Hello @taenri

I don't get it. Is there now a patch we can use for the problem in Windows 10 22H2? Still have the OneDrive Windows and in the other thread is closed with the reason it is opened here. We need some information.

[sylveon]

@sylveon - We are performing similar logic by using EnumThreadWindows to search for window handles created on our main thread with the title of "DesktopWindowXamlSource". Then we are calling ShowWindow(hwnd, SW_HIDE) to manually hide it. This seems to work well in our local testing using a virtual machine with the same version of Windows 10 that we know to be affected (build 19044, aka 21H2). On my VM, the issue persists without this manual hiding logic but fixed when our manual hiding logic is applied.

However, many of our users are still reporting this issue despite our best efforts. My understanding is that this bug has been fixed at the OS-level within the CoreWindow object itself in Windows 11 (from within the Windows.UI.Core namespace) but has not been patched for Windows 10.

Have you tried using ICoreWindowInterop? I've always found manual window searches to be fragile.

[github-actions]

This issue is stale because it has been open 180 days with no activity. Remove stale label or comment or this will be closed in 5 days.

[JJBrychell]

Because WinUI2 is in maintenance mode and that the issue has a work around (manually hiding the window using ShowWindow) and that there was a reported fix in later releases of Windows 10, we are closing this bug.

If the issue affects WinUi3, please feel free to reopen this issue.

[taenri]

@JJBrychell - Just to clarify, there are still some Windows versions where calling ShowWindow does not work. However, there is still another workaround that I think I should mention for others running into this issue:

Calling ITaskbarList::DeleteTab on the CoreWindow HWND will resolve the issue for good.
https://learn.microsoft.com/en-us/windows/win32/api/shobjidl_core/nf-shobjidl_core-itaskbarlist-deletetab