谁帮我解释下这个用用委托异步调用的例子

Question

这个是用委托异步调用的例子，但是我看不太懂，麻烦帮我解释下从按钮按下程序所走的流程是怎么样的，麻烦解释的详细点，谢谢！
private string Show(string content)
        {
            System.Threading.Thread.Sleep(5000);
            return "haha: " + content + "!";
        }        delegate string ShowEventHandler(string content);        private void button1_Click(object sender, EventArgs e)
        {
            ShowEventHandler showeventhandler = new ShowEventHandler(Show);
            showeventhandler.BeginInvoke("yoyo", new AsyncCallback(ReturnAsync), showeventhandler);
        }        private void ReturnAsync(IAsyncResult ar)
        {
            ShowEventHandler showeventhandler = (ShowEventHandler)ar.AsyncState;
            string result = showeventhandler.EndInvoke(ar);
            MessageBox.Show(result);
        }

Answer 1

BeginInvoke就异步Invoke同步，没什么可解释的，看msdn