WPF BlazorWebView: Unable to open multiple WPF windows with BlazorWebView content

Describe the bug

Opening a second WPF window with BlazorWebView content throws an InvalidOperationException.

To Reproduce

https://github.com/3bit/WpfBlazorMultipleWindowsTest demonstrates the problem. Just start the app and click on the button to open a new instance of the Blazor app in a second WPF window…

Stacktrace

System.Reflection.TargetInvocationException HResult=0x80131604 Message=Exception has been thrown by the target of an invocation. Source=System.Private.CoreLib StackTrace: at System.RuntimeMethodHandle.InvokeMethod(Object target, Span`1& arguments, Signature sig, Boolean constructor, Boolean wrapExceptions) at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture) at System.Delegate.DynamicInvokeImpl(Object[] args) at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs) at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler) at System.Windows.Threading.DispatcherOperation.InvokeImpl() at System.Windows.Threading.DispatcherOperation.InvokeInSecurityContext(Object state) at MS.Internal.CulturePreservingExecutionContext.CallbackWrapper(Object obj) at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state) — End of stack trace from previous location — at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at MS.Internal.CulturePreservingExecutionContext.Run(CulturePreservingExecutionContext executionContext, ContextCallback callback, Object state) at System.Windows.Threading.DispatcherOperation.Invoke() at System.Windows.Threading.Dispatcher.ProcessQueue() at System.Windows.Threading.Dispatcher.WndProcHook(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled) at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled) at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o) at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs) at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler) at System.Windows.Threading.Dispatcher.LegacyInvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs) at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam) at MS.Win32.UnsafeNativeMethods.DispatchMessage(MSG& msg) at System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame) at System.Windows.Threading.Dispatcher.PushFrame(DispatcherFrame frame) at System.Windows.Threading.Dispatcher.Run() at System.Windows.Application.RunDispatcher(Object ignore) at System.Windows.Application.RunInternal(Window window) at System.Windows.Application.Run() at WpfBlazorMultipleWindowsTest.App.Main()

This exception was originally thrown at this call stack: [External Code]

Inner Exception 1: InvalidOperationException: There is already a subscriber to the content ‘title’.

Further technical details

• ASP.NET Core version 6.0.100-rc.1.21463.6
• Microsoft Edge WebView2 Runtime 94.0.992.38
• Visual Studio 2022 Community 17.0.0 Preview 4.1

dotnet --info

.NET SDK (reflecting any global.json): Version: 6.0.100-rc.1.21463.6 Commit: e627d556a1

Runtime Environment: OS Name: Windows OS Version: 10.0.19043 OS Platform: Windows RID: win10-x64 Base Path: C:\Program Files\dotnet\sdk\6.0.100-rc.1.21463.6\

Host (useful for support): Version: 6.0.0-rc.1.21451.13 Commit: d7619cd4b1

.NET SDKs installed: 3.1.413 [C:\Program Files\dotnet\sdk] 5.0.102 [C:\Program Files\dotnet\sdk] 5.0.104 [C:\Program Files\dotnet\sdk] 5.0.401 [C:\Program Files\dotnet\sdk] 6.0.100-rc.1.21463.6 [C:\Program Files\dotnet\sdk]

.NET runtimes installed: Microsoft.AspNetCore.All 2.1.24 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All] Microsoft.AspNetCore.All 2.1.30 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All] Microsoft.AspNetCore.App 2.1.24 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 2.1.30 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 3.1.9 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 3.1.11 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 3.1.19 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 5.0.2 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 5.0.4 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 5.0.10 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 6.0.0-rc.1.21452.15 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.NETCore.App 2.1.24 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 2.1.30 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 3.1.9 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 3.1.11 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 3.1.15 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 3.1.19 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 5.0.2 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 5.0.4 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 5.0.10 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 6.0.0-rc.1.21451.13 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.WindowsDesktop.App 3.1.9 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App] Microsoft.WindowsDesktop.App 3.1.11 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App] Microsoft.WindowsDesktop.App 3.1.15 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App] Microsoft.WindowsDesktop.App 3.1.16 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App] Microsoft.WindowsDesktop.App 3.1.17 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App] Microsoft.WindowsDesktop.App 3.1.18 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App] Microsoft.WindowsDesktop.App 3.1.19 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App] Microsoft.WindowsDesktop.App 5.0.2 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App] Microsoft.WindowsDesktop.App 5.0.4 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App] Microsoft.WindowsDesktop.App 5.0.10 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App] Microsoft.WindowsDesktop.App 6.0.0-rc.1.21451.3 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

[3bit]

Thanks for looking into this so quickly!

[Eilon]

Indeed, avoiding a static/shared Dispatcher and creating a unique one in each BlazorWebView seems to do the trick.

Very interesting bug find!