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CoreWebView2.NavigateToString(String) method fails to load an HTML page

AdiGeo 20 Reputation points
2024-10-31T17:08:20.23+00:00

I am using an instance of WebView2 class to display some HTML content in a UI panel for a VS 2022 extension. I can retrieve the HTML content that I want to display in the WebView2 control as a string, and then I am trying to use myWebView2.CoreWebView2.NavigateToString(myHTMLPage) method to have the retrieved page displayed. The HTML content has a lot of JavaScript code in it, and while loading I am getting the following exception:

Uncaught DOMException: Failed to read the 'sessionStorage' property from 'Window': Access is denied for this document.

The JavaScript code needs to access the Window.sessionStorage, but I found that the value is undefined.

As a workaround, I save the HTML content in a temporary HTML file in the file system, and I use myWebView2.CoreWebView2.Navigate(myHTMLfile). This time the page loads and displays successfully. I delete the file once the page has loaded.

I wonder if when using the NavigateToString() method is there any solution to successfully display the page? I want to avoid creating a temporary file.

Thank you

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Accepted answer
  1. Viorel 118.4K Reputation points
    2024-10-31T20:25:37.1366667+00:00

    If the WebView is initialized, the next experimental button handler shows the usage of WebResourceRequested event, which allows to deliver the local contents:

    private void button1_Click( object sender, EventArgs e )
{
    webView.CoreWebView2.AddWebResourceRequestedFilter( "file://demo/*", CoreWebView2WebResourceContext.All );

    webView.CoreWebView2.WebResourceRequested += ( s, a ) =>
    {
        if( a.Request.Uri == "file://demo/test1.html" )
        {
            string html = @"<html>
<head>
<script>
function OnLoad()
{
   try 
   {                        
      alert( window.sessionStorage);
      alert( window.sessionStorage.getItem('myKey') );
      window.sessionStorage.setItem('myKey', Date.now() );
   } 
   catch(error) 
   {
      alert(error);
   }
}
</script>
</head>
<body onload=""OnLoad()"">
<h1>TEST</h1>
<p>
Hello!
</p>
</body>
</html>";

            var ms = new MemoryStream( Encoding.UTF8.GetBytes( html ) );
            a.Response = webView.CoreWebView2.Environment.CreateWebResourceResponse( ms, 200, "OK", "Content-Type: text/html" );
        }
    };

    webView.CoreWebView2.Navigate( "file://demo/test1.html" );
}

    Accessing the window.sessionStorage object in this sample should not fail. Maybe it will work in your tests too.

    For specific details and optimizations, see:

    1 person found this answer helpful.

1 additional answer

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  1. AdiGeo 20 Reputation points
    2024-10-31T21:01:02.0833333+00:00

    I just tried the solution you proposed, and works perfect.

    Many thanks,

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