static void Main(string[] args)
{
 Func<string,string> showMessage = ShowMessage;
 //设置了回调函数Completed,不能有返回值
 IAsyncResult result = showMessage.BeginInvoke("测试异步委托",new AsyncCallback(Completed),null);
 //半段异步是否结束
 while(!result.IsCompleted)
 {
  Console.WriteLine("主线程可以进行其它的操作！");
 }
 Console.ReadLine();
}
static string ShowMessage(string x)
{
 string current = string.Format("当前线程id为{0}",Thread.CurrentThread.ManagedThreadId);
 Thread.Sleep(3000);
 return string.Format("{0},输入为{1}", current, x);
}
static void Completed(IAsyncResult result)
{
 Console.WriteLine("异步完成！");
 //获取委托对象，并用EndInvoke方法获取返回结果
 AsyncResult _result = (AsyncResult) result;
 Func<string, string> showMessage = (Func<string, string>) _result.AsyncDelegate;
 //结束异步操作并输出
 Console.WriteLine(showMessage.EndInvoke(_result));
}