How to Fix unhandled exception in windows when closing a secondary window using the close button in the title bar

Question

When Multiple windows are opened using
Application.Current.OpenWindow()
Closing a window (not the primary application window) using the close button in the title bar (specially when the window is not in the foreground) raises an unhandled Exception.

Everything works fine when the windows are closed from within the code using
Application.Current.CloseWindow()

I Have reported the bug with details in :
https://github.com/dotnet/maui/issues/17787

Answer 1

Although the issue dose not appear on all windows 11 machines and I don't know why, here is the solution:

By adding the following lines to the MauiProgram.cs to be able to call the function

SetBorderAndTitleBar(false, false);

the problem was fixed. ( Just the lines between #If Windows and #endif.)

/// Need to use the 2 following name spaces:
#if WINDOWS 
using Microsoft.UI;
using Microsoft.UI.Windowing;
#endif

namespace MauiAppWindowTest
{
    public static class MauiProgram
    {
        public static bool NoTitleBar=false;
        public static MauiApp CreateMauiApp()
        {
            var builder = MauiApp.CreateBuilder();
            builder
                .UseMauiApp<App>()
                .ConfigureFonts(fonts =>
                {
                    fonts.AddFont("OpenSans-Regular.ttf", "OpenSansRegular");
                    fonts.AddFont("OpenSans-Semibold.ttf", "OpenSansSemibold");
                });
/// The Code below was added
#if WINDOWS
           builder.ConfigureLifecycleEvents(events =>
           {
               events.AddWindows(wndLifeCycleBuilder =>
               { 
                   wndLifeCycleBuilder.OnWindowCreated(window =>
                   {  
                          IntPtr nativeWindowHandle = WinRT.Interop.WindowNative.GetWindowHandle(window);
                          WindowId win32WindowsId = Win32Interop.GetWindowIdFromWindow(nativeWindowHandle);
                          AppWindow appWindow = AppWindow.GetFromWindowId(win32WindowsId);
                          if (appWindow.Presenter is OverlappedPresenter p)
                          {
							  /// Calling this function resolves the issue
                              p.SetBorderAndTitleBar(false, false);
                          }
                   });
               });
           });
#endif
/// Up to Here

            return builder.Build();
        }
    }
}