crossthread operations error

Question

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

This is the code in c# which when exec

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();
}