How to get return value when BeginInvoke/Invoke is called in C#

Question

I've this little method which is supposed to be thread safe. Everything works till i want it to have return value instead of void. How do i get the return value when BeginInvoke is called?

public static string readControlText(Control varControl) {
        if (varControl.InvokeRequired) {
            varControl.BeginInvoke(new MethodInvoker(() => readControlText(varControl)));
        } else {
            string varText = varControl.Text;
             return varText;
        }

    }

Edit: I guess having BeginInvoke is not nessecary in this case as i need value from GUI before the thread can continue. So using Invoke is good as well. Just no clue how to use it in following example to return value.

private delegate string ControlTextRead(Control varControl);
    public static string readControlText(Control varControl) {
        if (varControl.InvokeRequired) {
            varControl.Invoke(new ControlTextRead(readControlText), new object[] {varControl});
        } else {
            string varText = varControl.Text;
             return varText;
        }

    }

But not sure how to get value using that code either ;)

Answer 1

You have to Invoke() so you can wait for the function to return and obtain its return value. You'll also need another delegate type. This ought to work:

public static string readControlText(Control varControl) {
  if (varControl.InvokeRequired) {
    return (string)varControl.Invoke(
      new Func<String>(() => readControlText(varControl))
    );
  }
  else {
    string varText = varControl.Text;
    return varText;
  }
}