WPF WebView2 Error - source property cannot be set to null

Question

To authenticate an API service, it is required for the user to sign into a webpage. If the sign-in is valid, an authentication code is appended to the end of a redirected Uri. The authentication code is then used in the oauth to get the key, etc... To faciliate this, I have implemented WebView2:

        <wv2:WebView2 Name="webView"
                  Width="800"
                  Height="500"
                  Source="{Binding WebUri, Mode=TwoWay}">
        <i:Interaction.Triggers>
            <i:EventTrigger EventName="SourceChanged">
                <i:InvokeCommandAction Command="{Binding SourceChangedCommand}"/>
            </i:EventTrigger>
        </i:Interaction.Triggers>
    </wv2:WebView2>

I have validation logic in the viewmodel to recognize when the redirect uri contains the authentication code; this is done through the SourceChangedCommand that is called when the SourceChanged event is thrown on the WebView (following the navigation event lifecycle described here ). The SourceChangedCommand.Execute is as follows:

    public void Execute(object? parameter)
    {
        if (ValidateUri(_viewModel.WebUri.ToString()))
        {
            var str = _viewModel.WebUri.ToString().Substring(50);
            _navigationService.Authenticate(str);
        }
    }

Here is where I am running into a problem: I also have a NavigationService which navigates between viewmodels and changes view by datatemplates, etc... When navigating away from the view with the WebView2 (ie: changing data contexts on the parent view), I am given the following error:

The Source property cannot be set to null

This is extremely confusing as the source for the WebView2 is never actually set to null - it is maintained as the redirected Uri. What is going wrong here and how can I navigate away from this view?

Possible solutions I am exploring is creating a custom control extending WebView2 with a bool dependency property mapped to WebView2.Dispose(bool) -> if true, the webview will be disposed. This however seems like overkill and might bring up other issues relating to ObjectDisposedException 's.

Answer 1

I had the same problem and found it was because I was setting IsAsync=true on the binding.

Also inspect the properties you are binding to. They always need to be able to get a value that isn't null.

When my properties are initialized I set them to new Uri("about:blank").
Additionally, use this._myProp = new UriBuilder(value).Uri?? new Uri("about:blank") on the field set to ensure no nulls

Hey Microsoft how about a static Uri.Empty property with about:blank in it?

I hope this helps