Question

I am writing a toolbar for IE(6+). I have used the various sample bars from

codeproject.com (http://www.codeproject.com/KB/dotnet/IE_toolbar.aspx), and have a toolbar that works, registers unregisters etc. What I want the toolbar to do is to highlight divs within an html page as the users’ mouse moves over that div. So far the highlighting code works, but I would like to display the name of the div (if it exists) in a label on the toolbar (changing as the mouse moves etc).

I cannot for the life of me get this to happen and trying to debug it is a nightmare. As the assembly is hosted in IE, I suspect that I am causing an exception (in IE) by trying to update the text on the label from a thread that didn’t create that control, but because that exception is happening in IE, I don’t see it.

Is the solution to try to update the control in a thread-safe way using Invoke? If so how?

Here is the event code:

private void Explorer_MouseOverEvent(mshtml.IHTMLEventObj e) {       mshtml.IHTMLDocument2 doc = this.Explorer.Document as IHTMLDocument2;       element = doc.elementFromPoint(e.clientX, e.clientY);       if (element.tagName.Equals('DIV', StringComparison.InvariantCultureIgnoreCase))       {           element.style.border = 'thin solid blue;';           if (element.className != null)           {                UpdateToolstrip(element.className);           }       }        e.returnValue = false; } 

and here is an attempt at thread-safe update of the toolbar:

delegate void UpdateToolstripDelegate(string text);  public void UpdateToolstrip(string text) {      if (this.toolStripLabel1.InvokeRequired == false)      {          this.toolStripLabel1.Text = text;      }      else      {          this.Invoke(new UpdateToolstripDelegate(UpdateToolstrip), new object[] { text });      } } 

Any suggestions much appreciated.

Answer 1

I can’t really reproduce the issue (creating a test project for an IE toolbar is a tad too much work), but you can try this:

Add the following routine to a public static (extensions methods) class:

public static void Invoke(this Control control, MethodInvoker methodInvoker) {     if (control.InvokeRequired)         control.Invoke(methodInvoker);     else         methodInvoker(); } 

And then replace the section of similar code in the first block with this:

if (element.className != null) {     this.Invoke(() => toolStripLabel1.Text = element.className); } 

This is a sure-fire way of avoiding thread-safe issues in UI applications.