ScriptNotify in WPF WebView does not fire as expected

[rjmurillo]

I'm submitting a...

• Bug report (I searched for similar issues and did not find one)

Current behavior

Given the following code

MainWindow.xaml

<WPF:WebView
  x:Name="WebView"
  DOMContentLoaded="WebView_DOMContentLoaded"
  IsScriptNotifyAllowed="True"
  ScriptNotify="WebView_ScriptNotify"
  Source="http://www.example.com" />

MainWindow.xaml.cs

private void WebView_DOMContentLoaded(object sender, Microsoft.Toolkit.Win32.UI.Controls.Interop.WinRT.WebViewControlDOMContentLoadedEventArgs e)
{
  WebView.InvokeScriptAsync("eval", "window.external.notify('Hello world!');");
}

private void WebView_ScriptNotify(object sender, Microsoft.Toolkit.Win32.UI.Controls.Interop.WinRT.WebViewControlScriptNotifyEventArgs e)
{
  MessageBox.Show(e.Value, e.Uri?.ToString() ?? "Message from WebView", MessageBoxButton.OK);
}

The event handler WebView_ScriptNotify is never fired.

Expected behavior

The WebView_ScriptNotify event handler is fired

Minimal reproduction of the problem with instructions

Environment

Nuget Package(s): Microsoft.Toolkit.Win32.UI.Controls

Package Version(s): 3.0.0

Windows 10 Build Number:
- [ ] Creators Update (15063)
- [ ] Fall Creators Update (16299)
- [x April 2018 Update (17134)
- [x Insider Build (build number: 18209

App min and target version:
- [ ] Creators Update (15063)
- [ ] Fall Creators Update (16299)
- [x] April 2018 Update (17134)
- [ ] Insider Build (18209)

Device form factor:
- [x] Desktop
- [ ] Mobile
- [ ] Xbox
- [ ] Surface Hub
- [ ] IoT

Visual Studio 
- [x] 2017 (version: 15.7.8)
- [x] 2017 Preview (version: 15.8)

Filed on behalf of question on Stack Overflow: How to add a list of allowed URI's for WebView's “ScriptNotify” in a WPF app?

[rjmurillo]

There is a timing issue here where a number of methods can be invoked before initialization is completed. In this case, properties are read from the control via the dispatcher; however, navigation occurs and DOMLoadEvent is fired before initialization finishes setting properties for enabling JavaScript, IndexedDb, and ScriptNotify.

[rjmurillo]

Closed via #2347 and #2349