[Preview 4] MessageDialog is no longer functional

Describe the bug Showing a message dialog no longer works in a Win32 app using Preview 4

Steps to reproduce the bug Run the following code, for instance in a button click event:

            var dlg = new MessageDialog("Test");
            try
            {
                await dlg.ShowAsync();
            }
            catch (System.Exception ex)
            {
                Debug.WriteLine(ex.Message);
            }

See the following exception thrown in the catch:

Invalid window handle. (0x80070578)

Expected behavior Dialog displayed

Version Info

NuGet package version: [Microsoft.WinUI 3.0.0-preview4.210210.4]

Windows app type:

UWP	Win32
	Yes

Windows 10 version	Saw the problem?
Insider Build (xxxxx)
October 2020 Update (19042)
May 2020 Update (19041)
November 2019 Update (18363)
May 2019 Update (18362)
October 2018 Update (17763)
April 2018 Update (17134)
Fall Creators Update (16299)
Creators Update (15063)

Device form factor	Saw the problem?
Desktop
Xbox
Surface Hub
IoT

Additional context Workaround:

        [ComImport]
        [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
        [Guid("3E68D4BD-7135-4D10-8018-9FB6D9F33FA1")]
        internal interface IInitializeWithWindow
        {
            void Initialize(IntPtr hwnd);
        }

        [ComImport]
        [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
        [Guid("EECDBF0E-BAE9-4CB6-A68E-9598E1CB57BB")]
        internal interface IWindowNative
        {
            IntPtr WindowHandle { get; }
        }


// ...
            var dlg = new MessageDialog("Test");
            IInitializeWithWindow withWindow = dlg.As<IInitializeWithWindow>();
            var handle = this.As<IWindowNative>().WindowHandle;
            try
            {
                withWindow.Initialize(handle);
                await dlg.ShowAsync();
            }
            catch (System.Exception ex)
            {
                Debug.WriteLine(ex.Message);
            }

Alternative workaround without requiring knowledge of the current window:

        public static IAsyncOperation<IUICommand> ShowDialogAsync(string content, string title = null)
        {
            var dlg = new MessageDialog(content, title ?? "");
            var handle = GetActiveWindow();
            if (handle == IntPtr.Zero)
                throw new InvalidOperationException();
            dlg.As<IInitializeWithWindow>().Initialize(handle);
            return dlg.ShowAsync();
        }

        [ComImport]
        [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
        [Guid("3E68D4BD-7135-4D10-8018-9FB6D9F33FA1")]
        internal interface IInitializeWithWindow
        {
            void Initialize(IntPtr hwnd);
        }

        [DllImport("user32.dll")]
        private static extern IntPtr GetActiveWindow();

[dotMorten]

Yup I’m aware of the new helper, but it doesn’t really address the problem. If the dialog took the xamlroot as a parameter it would at least be a bit more obvious, perhaps combined with hiding the empty constructor from intellisense (since it needs to stay there for xaml support).

And speaking of that helper: It isn’t even clear what type it takes as a parameter (just any object), nor is there any intellisense to tell me anything:

When you don’t hook up the window handle or root (because how are you supposed to know you need to?), you get really really poor error messages, not help messages (it’s not invalid, it’s just not set):

At least you can get a bit further with some extension methods, but we shouldn’t have to do this:

All of this ultimately leads to an extremely frustrating and off-putting developer experience. I feel a bit like beating a dead horse, since I’ve been making this same point over and over. It’s one thing that WinUI “works” and can do what it needs to, but that doesn’t help, if the developer experience is so frustrating we give up before we really get into using it.

[dotMorten]

Remember that MessageDialog is an old Windows 8 era system API

Again just an excuse. WinUI needs a message dialog that fits into the WinUI model of things. We shouldn’t have to be doing these crazy hacks to make basic things work. But we’re currently left with no choice.