Question

please consider the following scenario for .net 2.0:

I have an event that is fired on system.Timers.Timer object. The subscriber then adds an item to a Windows.Forms.Listbox upon receiving the event. This results in a cross-thread exception.

My question is what would be the best way to handle this sort of situation. The solutions that I have come up with is as follows:

private   delegate void messageDel(string text);
private   void ThreadSafeMsg(string text)
{
  if (this.InvokeRequired)
  {
    messageDel d = new messageDel(ThreadSafeMsg);
    this.Invoke(d, new object[] { text });
  }
  else
  {
  listBox1.Items.Add(text);
  listBox1.Update();
  }
}

 // event
void Instance_Message(string text)
{
  ThreadSafeMsg(text);
}

Is this the optimum way to handle this in .net 2? What about .net 3.5?

Answer 1

There’s no point in using Control.InvokeRequired, you know that it always is. The Elapsed event is raised on a threadpool thread, never the UI thread.

Which makes it kinda pointless to use a System.Timers.Timer, just use the System.Windows.Forms.Timer. No need to monkey with Control.Begin/Invoke, you can’t crash your program with an ObjectDisposedException when the event is raised just as the user closes the form.