/// 

/// 开始执行异步操作.
/// 
/// 委托方法的参数
/// 
/// 
/// 
IAsyncResult BeginInvoke(int param, AsyncCallback callback, Object @object);

/// 

/// 结束执行异步操作，并且返回异步操作结果.
/// 
/// 
/// 委托方法的返回类型
string EndInvoke(IAsyncResult result);

/// 

/// 定义一个委托类型
/// 
public delegate string Del();

/// 

/// 任务类
/// 
public class TaskClass
{
  public static string SleepTask()
  {
    Console.WriteLine("异步线程(ThreadId = {0})开始执行睡眠任务，睡眠3s.\n", Thread.CurrentThread.ManagedThreadId);

    Thread.Sleep(3000);

    Console.WriteLine("异步线程(ThreadId = {0})苏醒，睡眠任务执行结束.\n", Thread.CurrentThread.ManagedThreadId);

    return "异步线程执行成功.\n";
  }
}
  
/// 

/// 异步编程实现类（主线程不会阻塞）
/// 
public class AsynCallbackClass
{
  public static string result;

  public static void Main(string[] args)
  {
    Console.WriteLine("主线程(ThreadId = {0})开始执行.\n", Thread.CurrentThread.ManagedThreadId);

    Del del = new Del(TaskClass.SleepTask);

    Console.WriteLine("主线程(ThreadId = {0})调用BeginInvoke()方法执行异步任务.\n", Thread.CurrentThread.ManagedThreadId);

    //开始执行异步操作，TaskClass.SleepTask无参数，Callback为定义的回调方法.
    del.BeginInvoke(Callback, null);

    Console.WriteLine("主线程(ThreadId = {0})继续执行.\n", Thread.CurrentThread.ManagedThreadId);

    Thread.Sleep(5000);

    //输出异步任务返回的结果
    Console.WriteLine(result);

    Console.WriteLine("主线程(ThreadId = {0})执行结束.\n", Thread.CurrentThread.ManagedThreadId);
  }

  /// 

  /// 回调方法
  /// 
  /// 
  public static void Callback(IAsyncResult ar)
  {
    AsyncResult asyncResult = ar as AsyncResult;

    if (asyncResult == null) { return; }

    Del del = asyncResult.AsyncDelegate as Del;

    if (del == null) { return; }

    Console.WriteLine("回调方法中调用EndInvoke()方法，获取异步任务结果.\n", Thread.CurrentThread.ManagedThreadId);
    
    //结束执行异步操作，并返回异步任务结果.
    result = del.EndInvoke(ar);
  }
}