以下内容摘之于ＭＳＤＮ，并结合自己加一些自己的看法：我学得这可以让让想了解用BeginInvoke来进生异步调用的人会有一个全面的了解：
我觉得所为的异步调用是通过１．Thread.Sleep(),来控制主线程与BenginInovke线程的执行先后顺序．
２．通过ＥndInvoke来阻塞让线程，让ＢeginInvoke线程来执行．
３．回调方法无论如何都是要等等ＢeginInvoke所代理的方法先执行完，它才会执行．但，它们用的都是BeginInvoke 的线程；
如果去掉上面的条件，那么就变成同步调用啦．
以下提代码测试：
using System;using System.Threading; ／／公共测试类
public class AsyncDemo {
// The method to be executed asynchronously. public string TestMethod(int callDuration, out int threadId) { Console.WriteLine("Test method begins.");//使用该线程休眠，让主线程完成ＥndInvoke这之前的代码．为什么这么说呢，因为ＥndInove会阻塞主线程直到调／／用完毕，并取得返回值：
Thread.Sleep(callDuration); threadId = AppDomain.GetCurrentThreadId(); return "MyCallTime was " + callDuration.ToString();
}
}／／使用 EndInvoke 等待异步调用测试主类public class AsyncMain {
static void Main(string[] args) {
// The asynchronous method puts the thread id here. int threadId; // Create an instance of the test class. AsyncDemo ad = new AsyncDemo(); // Create the delegate. AsyncDelegate dlgt = new AsyncDelegate(ad.TestMethod); // Initiate the asychronous call. IAsyncResult ar = dlgt.BeginInvoke(3000, out threadId, null, null);／／注意，在此,threadid并没有改变．直到ＥndInove;在这里这要提到一个得得就是，我们知道，定义Ｄelegate的／／时候其形参不能包含有out关关键字的，我也不太明白这里，应该是个特例吧！ Thread.Sleep(0); Console.WriteLine("Main thread {0} does some work.", AppDomain.GetCurrentThreadId()); // Call EndInvoke to Wait for the asynchronous call to complete, // and to retrieve the results. string ret = dlgt.EndInvoke(out threadId, ar); Console.WriteLine("The call executed on thread {0}, with return value \"{1}\".", threadId, ret); }}／／使用 WaitHandle 等待异步调用测试主类public class AsyncMain { static void Main(string[] args) { // The asynchronous method puts the thread id here. int threadId; // Create an instance of the test class. AsyncDemo ad = new AsyncDemo(); // Create the delegate. AsyncDelegate dlgt = new AsyncDelegate(ad.TestMethod); // Initiate the asychronous call. IAsyncResult ar = dlgt.BeginInvoke(3000, out threadId, null, null); Thread.Sleep(0); Console.WriteLine("Main thread {0} does some work.", AppDomain.GetCurrentThreadId()); // Wait for the WaitHandle to become signaled. ar.AsyncWaitHandle.WaitOne();／／上面一句可以让Ｉnvoke线程先停止运行，先执行下面语句直到EndInvoke.
//可以在这里添加你要运行的代码． // Perform additional processing here. // Call EndInvoke to retrieve the results. string ret = dlgt.EndInvoke(out threadId, ar); Console.WriteLine("The call executed on thread {0}, with return value \"{1}\".", threadId, ret); }}／／轮询异步调用完成测试主类public class AsyncMain { static void Main(string[] args) { // The asynchronous method puts the thread id here. int threadId; // Create an instance of the test class. AsyncDemo ad = new AsyncDemo(); // Create the delegate. AsyncDelegate dlgt = new AsyncDelegate(ad.TestMethod); // Initiate the asychronous call. IAsyncResult ar = dlgt.BeginInvoke(3000, out threadId, null, null); // Poll while simulating work.／／下面语句控主线程让，让Invoke线程运行完毕;
while(ar.IsCompleted == false) { Thread.Sleep(10); } // Call EndInvoke to retrieve the results. string ret = dlgt.EndInvoke(out threadId, ar); Console.WriteLine("The call executed on thread {0}, with return value \"{1}\".", threadId, ret); }}／／异步调用完成时执行回调方法测试主类public class AsyncMain { // Asynchronous method puts the thread id here. private static int threadId; static void Main(string[] args) { // Create an instance of the test class. AsyncDemo ad = new AsyncDemo(); // Create the delegate. AsyncDelegate dlgt = new AsyncDelegate(ad.TestMethod); // Initiate the asychronous call. Include an AsyncCallback // delegate representing the callback method, and the data // needed to call EndInvoke. IAsyncResult ar = dlgt.BeginInvoke(3000, out threadId, new AsyncCallback(CallbackMethod), dlgt ); Console.WriteLine("Press Enter to close application."); Console.ReadLine(); } // Callback method must have the same signature as the // AsyncCallback delegate.//下面那个回调方法，只有等到BeginInvoke所调用的代理方法执行完毕才会执行，但它们用的是同一条线程，而不是与主线程相同．
static void CallbackMethod(IAsyncResult ar) { // Retrieve the delegate. AsyncDelegate dlgt = (AsyncDelegate) ar.AsyncState; // Call EndInvoke to retrieve the results. string ret = dlgt.EndInvoke(out threadId, ar); Console.WriteLine("The call executed on thread {0}, with return value \"{1}\".", threadId, ret); }}