Question

      if (listBox1.InvokeRequired)
       {
           listBox = new StringBuilder(this.listBox1.Text);
       }

This is the code in c# which when executed produces an invalid cross thread operation error for listBox1 which is a listbox in my form.
Could u guys please tell me why??
I am using the invokeRequired method too and am not changing the contents of the listbox either.

Answer 1

InvokeRequired only tells you that an Invoke is necessary in order to validly access the element. It doesn’t make the access legal. You must use the invoke method to push the update to the appropriate thread

Action update = () => listbox = new StringBuilder(this.listBox1.Text);
if (listBox1.InvokeRequired) {
  listBox1.Invoke(update);
} else {
  update();
}