简要介绍：
1.定义异步执行需要调用的方法
2.定义具有与异步执行方法相同签名的委托(Delegate)；
3.调用 BeginInvoke 和 EndInvoke 方法。
3.1. BeginInvoke 方法用于启动异步调用。它与需要异步执行的方法具有相同的参数，
只不过还有两个额外的参数。BeginInvoke 立即返回，不等待异步调用完成。
BeginInvoke 返回 IasyncResult，可用于监视调用进度。
3.2. EndInvoke 方法用于检索异步调用结果。调用 BeginInvoke 后可随时调用 EndInvoke 方法；
如果异步调用未完成，EndInvoke 将一直阻塞到异步调用完成。
EndInvoke 的参数包括需要异步执行的方法的 out 和 ref 参数以及由 BeginInvoke 返回的 IAsyncResult。
3.3.调用了 BeginInvoke 后，可以：
* 进行某些操作，然后调用 EndInvoke 一直阻塞到调用完成。
* 使用 IAsyncResult.AsyncWaitHandle 获取 WaitHandle，使用它的 WaitOne 方法将执行一直阻塞到发出 WaitHandle 信号，然后调用 EndInvoke。
* 轮询由 BeginInvoke 返回的 IAsyncResult，确定异步调用何时完成，然后调用 EndInvoke。
* 将用于回调方法的委托传递给 BeginInvoke。该方法在异步调用完成后在 ThreadPool 线程上执行，它可以调用 EndInvoke。
//具体代码如下:
using System;
using System.Threading;
//The example of using delegate
namespace DelegateCallAsynchronousMethods
{
class AsyncFileDelegate
{
/*
*这是需要异步执行的方法，COPY一个文件
*/
public void CopyFile(String fileName, out bool result)
{
Console.WriteLine("Move file "+fileName+"...");
for (int i = 0; i < 10; i++)
{
Thread.Sleep(200);
Console.WriteLine("Move file is running..." + i);
}
Console.WriteLine("Move file finished");
result = true;
}
/*
*定义COPY文件的委托，将来CopyFile方法就委托给它去异步执行
*/
public delegate void CopyFileDelegate(String fileName, out bool result);//Declare copy file delegate
static void Main()
{
bool result;
AsyncFileDelegate aa = new AsyncFileDelegate();
// 开始委托方法，以后都由copyFile这个变量来做事
CopyFileDelegate copyFile = new CopyFileDelegate(aa.CopyFile);
Console.WriteLine("[Main] Invoking the asynchronous "+" Copy file method");
//委托调用异步方法去执行
IAsyncResult iAR = copyFile.BeginInvoke("songlin.txt", out result, null, null);
// 主方法不用等待COPY FILE方法，继续自己的事情
Console.WriteLine("[Main] Doing other work");
for (int i = 0; i < 10; i++)
{
Thread.Sleep(200);
Console.WriteLine("[Main]MainMethod is running..."+i);
}
Console.WriteLine(" [Main] Waiting for file transformation to finish");
/* 主方法自己的事情做完，开始检查COPYFILE有没有完成。
* 使用它的 WaitOne 方法将执行一直等到发出 WaitHandle 信号，然后调用 EndInvoke。
* 注意：异步调用完成时会发出 WaitHandle 信号，可以通过WaitOne 来等待它*/
iAR.AsyncWaitHandle.WaitOne();
Console.WriteLine("[Main] Copy file finished, cleaning up");
/* EndInvoke 方法用于检索异步调用结果。调用 BeginInvoke 后可随时调用 EndInvoke 方法；
* 如果异步调用未完成，EndInvoke 将一直阻塞到异步调用完成。
*/
copyFile.EndInvoke(out result, iAR);
Console.WriteLine("[Main] The result is {0}", result);
Console.ReadLine();
}
};
}
下面是输出结果，可以看出copyfile方法和主方法是异步执行的。
----------------------------------------------------------------------------------------------
[Main] Invoking the asynchronous Copy file method
[Main] Doing other work
Move file songlin.txt...
[Main]MainMethod is running...0
Move file is running...0
[Main]MainMethod is running...1
Move file is running...1
[Main]MainMethod is running...2
Move file is running...2
[Main]MainMethod is running...3
Move file is running...3
[Main]MainMethod is running...4
Move file is running...4
[Main]MainMethod is running...5
Move file is running...5
[Main]MainMethod is running...6
Move file is running...6
[Main]MainMethod is running...7
Move file is running...7
[Main]MainMethod is running...8
Move file is running...8
[Main]MainMethod is running...9
[Main] Waiting for file transformation to finish
Move file is running...9
Move file finished
[Main] Copy file finished, cleaning up
[Main] The result is True
以下是代码例子，模拟了文件拷贝。每个文件的拷贝方法都是在异步方式下运行，同时主方法依然运行。
在主方法的最后会等待直到所有的异步方法执行完成。
namespace WindowsApplication2
{
public class AsyncFileCopy
{
//Declare copy file delegate, will use this to invoke real copy file method
public delegate string CopyFileDelegate(int fileSize);
//The real file copy method, we simulate file copy with thread sleep
public String CopyFile(int fileSize)
{
switch (fileSize)
{
case 1:
Console.WriteLine("File 1 copy start...");
Thread.Sleep(1000);
Console.WriteLine("File 1 copy finished");
return "One";
case 2:
Console.WriteLine("File 2 copy Start...");
Thread.Sleep(2000);
Console.WriteLine("File 2 copy Finished");
return "Two";
case 3:
Console.WriteLine("File 3 copy Start...");
Thread.Sleep(3000);
Console.WriteLine("File 3 copy Finished");
return "Three";
default:
return "default";
}
}
public void ExecuteCopy()
{
List<WaitHandle> list = new List<WaitHandle>();
Console.WriteLine("Main method Start");
//Init coyp file delegate
CopyFileDelegate dlg = new CopyFileDelegate(CopyFile);
//Assume we have 4 different size files.
//Section below will let each file be copied in Async model
for (int i = 0; i < 4; i++)
{
//Let copy file executed in Async model, main thread continue
IAsyncResult ar = dlg.BeginInvoke(i, null, null);
list.Add(ar.AsyncWaitHandle);
Console.WriteLine("Main method still working" + i);
Thread.Sleep(10);//simulate main method cost some time
}
//Ensure all Async method finished before return from main method
System.Threading.WaitHandle.WaitAll(list.ToArray());
Console.WriteLine("Main method finished");
}
public static void Main(string[] args)
{
AsyncFileCopy test = new AsyncFileCopy();
test.ExecuteCopy();
}
}
}
