UWP Visual C# WebView InvokeScript to change CSS throws Exception

Question

I am trying to change the CSS of a loaded Website in a WebView (not local) by injecting a Javascript Function. I found these two Articles ( Article 1 , Article 2 ) but after implementing both Versions I always get the following Exception: System.NotImplementedException {"The method or operation is not implemented."}

This is my Code so far:

MainPage.xml

...
  <WebView x:Name="WebView" LoadCompleted="webViewCSS_LoadCompleted"/>
...

MainPage.xaml.cs

...
private void webViewCSS_LoadCompleted (object sender, NavigationEventArgs e)
  {
     addCss();
  }

private void addCss()
  {
     try
        {
            StringBuilder sb = new StringBuilder();
            sb.Append("function setCSS() { ");
            sb.Append("document.getElementsByClassName('app')[0].style.width = '100%';");
            sb.Append("} ");

            string script = sb.ToString();
            WebView.InvokeScript("eval", new string[] { script });
            WebView.InvokeScript("eval", new string[] { "setCSS()" });
        } catch (Exception ex)
        {

        }
    }
...

I dont know why it is throwing an Exception. I hope the Information that I have given is enough. If not please get back to me :-)

Thank you in advance for your answer

Answer 1

WebView.InvokeScript method may be unavailable for releases after Windows 8.1. Instead, we need to use WebView.InvokeScriptAsync method .

You can refer to WebView class , there are examples in the Remarks part of the official document:

you can use InvokeScriptAsync with the JavaScript eval function to inject the content into the web page.