COMException -2147023728 when calling BackgroundTaskRegistration in MAUI WinUI project

[Mvk3aJKQh]

Description

I created both a brand new single and multi-app MAUI project, and added System.Diagnostics.Debug.WriteLine(Windows.ApplicationModel.Background.BackgroundTaskRegistration.AllTasks.Count); to the WinUI App constructor after InitializeComponent(); and it throws this exception. Works for .NET 8, but not for .NET 9. Creating the new project for .NET 8, then selecting .NET 9 for Windows prompts to install the Android SDKs when building.

Steps to Reproduce

1. Create a new .NET 9 MAUI project
2. Add System.Diagnostics.Debug.WriteLine(Windows.ApplicationModel.Background.BackgroundTaskRegistration.AllTasks.Count); to the WinUI App constructor after InitializeComponent();
3. Run

Link to public reproduction project repository

https://github.com/Mvk3aJKQh/COMException-2147023728

Version with bug

9.0.14 SR1.4

Is this a regression from previous behavior?

Yes, this used to work in .NET MAUI

Last version that worked well

.NET 8

Affected platforms

Windows

Affected platform versions

Windows 10 build 19045.5371

Did you find any workaround?

No response

Relevant log output

System.Runtime.InteropServices.COMException
  HResult=0x80070490
  Message=
  Source=WinRT.Runtime
  StackTrace:
   at WinRT.ExceptionHelpers.<ThrowExceptionForHR>g__Throw|38_0(Int32 hr)
   at WinRT.ExceptionHelpers.ThrowExceptionForHR(Int32 hr)
   at ABI.Windows.ApplicationModel.Background.IBackgroundTaskRegistrationStaticsMethods.get_AllTasks(IObjectReference _obj)
   at Windows.ApplicationModel.Background.BackgroundTaskRegistration.get_AllTasks()
   at Product.Platforms.Windows.App..ctor() in {ProjectPath}\Platforms\Windows\App.xaml.cs:line 11
   at Product.Platforms.Windows.Program.<>c.<Main>b__0_0(ApplicationInitializationCallbackParams p) in {OutputPath}\obj\Debug\net9.0-windows10.0.19041.0\win10-x64\Platforms\Windows\App.g.i.cs:line 29
   at ABI.Microsoft.UI.Xaml.ApplicationInitializationCallback.Do_Abi_Invoke(IntPtr thisPtr, IntPtr p)

[Mvk3aJKQh]

Added link to repository

[RoiChen001]

I can repro this issue at Windows platform on the latest 17.13 Preview 5(9.0.30 & 9.0.14), but the exception does not exist in 8.0.100.

[mattleibow]

Is this a packaged or unpackaged app?

Seems to be this: microsoft/WindowsAppSDK#4201

Even this: microsoft/CsWinRT#1518

[mattleibow]

@RoiChen001 are you able to use .net 8 and upgrade the Windows App SDK to the latest?

[mattleibow]

Does this happen on Windows 11 AND Windows 10?

[Mvk3aJKQh]

Looks like a problem with the WindowsPackageType element in the project file. In a new .NET 8 project, this element isn't required, though the properties UI has the "Create a Windows MSIX package." option already selected. When I deselect this option, same exception occurs. In a new .NET 9 project, this element is required, already present, and removing it from the project file will cause a different exception. This option is not already selected in the properties UI, and selecting it changes the value of the WindowsPackageType element from "None" to "MSIX". And this corrects the problem raised in this issue.

In the new .NET 8 project, deselecting the "Create a Windows MSIX package." option adds the WindowsPackageType element to the project file with a value of "None". This results in the same exception raised in this issue. Reselecting this option then changes the value of this element to "MSIX". However, this element can be removed from the .NET 8 project file without causing an exception.

[dotnet-policy-service]

Thanks for the issue report @Mvk3aJKQh! This issue appears to be a problem with Visual Studio, so we ask that you use the VS feedback tool to report the issue. That way it will get to the routed to the team that owns this experience in VS.

If you encounter a problem with Visual Studio, we want to know about it so that we can diagnose and fix it. By using the Report a Problem tool, you can collect detailed information about the problem, and send it to Microsoft with just a few button clicks.

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[Mvk3aJKQh]

Well I can't find information about whether (MSIX) packaging is required to use WinRT. The exception suggests that it is required, since a value of "None" causes the exception in both projects. This would seem to be an issue with an API, and not Visual Studio. The properties UI in Visual Studio does something different between newly created .NET 8 and .NET 9 projects, but the issue is the same when deselecting the "Create a Windows MSIX package." option in the .NET 8 project. So we still have a requirement to create an MSIX package to access the Windows.ApplicationModel.Background namespace.