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Editorial Team
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Asked: 2026-06-13T00:09:39+00:00

I am having problem using webbrowser control to correctly display html. My goal is

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I am having problem using webbrowser control to correctly display html. My goal is to add custom html to a webbrowser control, have it displayed, and save the screenshot of that as png. Currently I am using Document.OpenNew and Document.Write(htmlText) and Application.DoEvents(). However since I am running this in a background thread, sometimes it deadlocks. I know the culprit is Application.DoEvents() which is giving me troubles.

However, if I remove that and set the html directly to DocumentText property, how do I know when it is fully “rendered” or loaded. I used the DocumentCompleted Event but that does not seem to work since the image that is saved is still empty even after the event fires.

I also have the thread as STA.

Here is the existing code:

Thread th = new Thread(new ThreadStart(createImage));
th.SetApartmentState(ApartmentState.STA);
th.Start();
th.Join(TIMEOUT);

private void createImage() {
 var browser = new WebBrowser();
 var doc = browser.Document;
 doc.OpenNew(false);
 doc.Write("<html><body>....</body><html>)");
 //loop for few seconds
 for(int i=0; i<20; i++)
 {
   Application.DoEvents();
   Thread.Sleep(100);
 }
 //save to file as png.
}

Here is the code I am trying:

private void createImage() {
 var browser = new WebBrowser();
 bool docComplete = false;
 browser.DocumentCompleted += new WebBrowserDocumentCompletedEventHandler(
                (Object sender, WebBrowserDocumentCompletedEventArgs args) =>
                { docComplete = true; }
                );
 browser.DocumentText = "<html>.....";
 while (!_docComplete)
 {                    
    Thread.Sleep(100);
  }
 // save image
 // :-( not working
}
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1 Answer

  1. Editorial Team

    You have to create thread as STA, that is only the way to run WebBrowser in a background thread.

    bw.SetApartmentState(ApartmentState.STA);

    There is no information about waiting in HtmlDocument.Write Method. If is yet required then you can add DocumentCompleted handler instead of DoEvents

    private void captureImageThread(string html) { 
   var thread = new Thread(() => { 
       var browser = new WebBrowser(); 
       browser.DocumentCompleted += browser_DocumentCompleted; 
       browser.DocumentText = html;
       Application.Run(); 
   }); 
   thread.SetApartmentState(ApartmentState.STA); 
   thread.Start(); 
} 

void browser_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e) { 
   var br = sender as WebBrowser; 
   // save image here
   Application.ExitThread();   // Stops the thread 
}
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