System.Runtime.InteropServices.COMException: 'Invalid window handle. (0x80070578) about winui-gallery

[yegorisB]

   Everything is all right If you use this:
   
           private async void OpenButton_Click(object sender, RoutedEventArgs e)
    {

        //https://github.com/microsoft/WindowsAppSDK/issues/1188
        //More info on obtaining the HWND
        var filePicker = new FileOpenPicker();

        // Get the current window's HWND by passing in the Window object
        var hwnd = WinRT.Interop.WindowNative.GetWindowHandle(this);

        // Associate the HWND with the file picker
        WinRT.Interop.InitializeWithWindow.Initialize(filePicker, hwnd);

        // Use file picker like normal!
        filePicker.FileTypeFilter.Add("*");
        var file = await filePicker.PickSingleFileAsync();

        if (file != null)
        {
            using (Windows.Storage.Streams.IRandomAccessStream randAccStream =
                await file.OpenAsync(Windows.Storage.FileAccessMode.Read))
            {
                // Load the file into the Document property of the RichEditBox.
                editor.Document.LoadFromStream(Microsoft.UI.Text.TextSetOptions.FormatRtf, randAccStream);
            }
        }
    }

instead of this:

    private async void OpenButton_Click(object sender, RoutedEventArgs e)
    {

        //https://github.com/microsoft/WindowsAppSDK/issues/1188
        //More info on obtaining the HWND
        var filePicker = new FileOpenPicker();

        // Get the current window's HWND by passing in the Window object
        var hwnd = WinRT.Interop.WindowNative.GetWindowHandle(this);

        // Associate the HWND with the file picker
        WinRT.Interop.InitializeWithWindow.Initialize(filePicker, hwnd);

        // Use file picker like normal!
        filePicker.FileTypeFilter.Add("*");
        var file = await filePicker.PickSingleFileAsync();

        if (file != null)
        {
            using (Windows.Storage.Streams.IRandomAccessStream randAccStream =
                await file.OpenAsync(Windows.Storage.FileAccessMode.Read))
            {
                // Load the file into the Document property of the RichEditBox.
                editor.Document.LoadFromStream(Microsoft.UI.Text.TextSetOptions.FormatRtf, randAccStream);
            }
        }
    }