Resetting Window.DataContext with two-way bound MVVM model raises NotImplementedException

[PatrickHofman]

Description
A NotImplementedException is thrown when binding two-way to a MVVM model, and resetting that model to null. This bug seems related to #1330, but has some specifics that could mean there is a secondary bug, or at least a good test case.

Call stack on this.DataContext = default;:

at Microsoft.Web.WebView2.Wpf.WebView2.SourcePropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)

Version
SDK: 1.0.864.35
Runtime: Unknown
Framework: WPF
OS: Win10 21H1 19043.1055

Repro Steps

• Create a WPF app (net472)
• Add this code in the MainWindow.xaml:

<wv2:WebView2 x:Name="Browser" Source="{Binding Url, Mode=TwoWay}"></wv2:WebView2>

• Replace the code in the MainWindow.xaml.cs with this:

public partial class MainWindow : Window
{
    public MainWindow()
    {
        ViewModel m = new ViewModel()
        { Url = new Uri("https://google.com")
        };

        this.InitializeComponent();

        this.DataContext = m;
    }

    /// <summary>
    /// Raises the System.Windows.Window.Closed event.
    /// </summary>
    /// <param name="e">An System.EventArgs that contains the event data.</param>
    protected override void OnClosed(EventArgs e)
    {
        base.OnClosed(e);

        //
        // Reset data context and model to default.
        //
        this.DataContext = default;
    }
}

public class ViewModel : DependencyObject
{
    /// <summary>
    /// Gets the Url dependency property.
    /// </summary>
    public static readonly DependencyProperty UrlProperty = DependencyProperty.Register(nameof(Url), typeof(Uri), typeof(ViewModel));

    /// <summary>
    /// Gets or sets the URL.
    /// </summary>
    public Uri Url
    {
        get { return (Uri)this.GetValue(UrlProperty); }
        set { this.SetValue(UrlProperty, value); }
    }
}

Open the app, close the app after the Google home page has loaded. On closing, an exception is raised.

Expected no exceptions to be raised and the unbound value to be allowed, or rewritten to something like about:blank.

[champnic]

Agreed this looks the same as #1330, but thanks for opening and including the extra test case! I've included a link to this info in our tracking bug.