Interview Question: When do you use Control.InvokeRequired Control.Invoke or Control.BeginInvoke?

Question

I recently had one of these very bad interviews in which they play a good cop / bad cop with you. All that I answered was not enough for one of them, and my confidence declined with each passing minute. His last question, which really confused me, was this:

if InvokeRequired is required for control, will there be a difference in the execution of .Invoke or .BeginInvoke?

Let me show you an example of how I understand it:

public delegate string WorkLongDelegate(int i);

var del = new WorkLongDelegate(WorkLong);
var callback = new AsyncCallback(CallBack);
del.BeginInvoke(3000, callback, del);

public string WorkLong(int i)
{
      Thread.Sleep(i);
      return (string.Format("Work was done within {0} seconds.", i));            
}

private void CallBack(IAsyncResult ar)
{
    var del = (WorkLongDelegate) ar.AsyncState;
    SetText2(del.EndInvoke(ar));
}

private void SetText2(string s)
{
   if(InvokeRequired)
   {
       // What is the difference between BeginInvoke and Invoke in below?
       BeginInvoke(new MethodInvoker(() => textBox1.Text = s)); 
   }
   else
   {
       textBox1.Text = s;
   }
}

, BeginInvoke , Invoke . . , , Invoke. -, , ?

Answer 1

Invoke . .

, , , , . , - , , , .

, - ( , ), Invoke. , BeginInvoke, Invoke. :)

Answer 2

Invoke() - , , . Invoke() , Object, .

- , , . Invoke() , . , , , , . 40 . Invoke(), . , , . , , .

(), BeginInvoke(). , Invoke(), . BeginInvoke, , , , . - , Invoke(). , , . , .

Answer 3

, asnyc, , .

Usually this should be faster (for a background thread) from what I am doing.