1、創建線程的一種簡單方法是定義一個委托，並異步調用它。
1 using System;
2 using System.Threading;
3
4 delegate int WaitAWhileDelegate(int data, int ms);
5
6 class Program
7 {
8 static void Main(string[] args)
9 {
10 WaitAWhileDelegate d = WaitAWhile;
11 int data = 1;
12 int ms = 3000;
13 IAsyncResult a = d.BeginInvoke(data, ms, null, null);
14 while (!a.IsCompleted)
15 {
16 Console.Write("*");
17 Thread.Sleep(100);
18 }
19 int result = d.EndInvoke(a);
20 Console.WriteLine("\nresult: {0}", result);
21 }
22
23 static int WaitAWhile(int data, int ms)
24 {
25 Console.WriteLine("WaitAWhile started.");
26 Thread.Sleep(ms);
27 Console.WriteLine("WaitAWhile completed.");
28 return ++data;
29 }
30 }
增加代碼中第17行的Sleep方法的參數值，輸出的星號的個數會減少，反之會增加。
運行結果：
2、IAsyncResult有一個名字叫AsyncWaitHandle的屬性，該屬性的類型是WaitHandle類。該類的WaitOne方法會“將一個超時時間作為可選的第一個參數，在其中可以定義要等待的最長時間”。
1 using System;
2 using System.Threading;
3
4 class Program
5 {
6 delegate int WaitAWhileDelegate(int data, int ms);
7
8 static void Main(string[] args)
9 {
10 WaitAWhileDelegate d = new WaitAWhileDelegate(WaitAWhile);
11 int data = 1;
12 int ms = 3000;
13 IAsyncResult a = d.BeginInvoke(data, ms, null, null);
14 while (true)
15 {
16 Console.Write("*");
17 if (a.AsyncWaitHandle.WaitOne(50, false))
18 {
19 Console.WriteLine("Can get the result now.");
20 break;
21 }
22 }
23 int result = d.EndInvoke(a);
24 Console.WriteLine("\nresult: {0}", result);
25 }
26
27 static int WaitAWhile(int data, int ms)
28 {
29 Console.WriteLine("WaitAWhile started.");
30 Thread.Sleep(ms);
31 Console.WriteLine("WaitAWhile completed.");
32 return ++data;
33 }
34 }
運行結果：
3、等待結果的第三種方式是異步回調。IAsyncResult還有一個名字叫AsyncState的屬性。該屬性可以強制類型轉換為它的委托。
1 using System;
2 using System.Threading;
3
4 class Program
5 {
6 delegate int WaitAWhileDelegate(int data, int ms);
7
8 static void Main(string[] args)
9 {
10 WaitAWhileDelegate d = new WaitAWhileDelegate(WaitAWhile);
11 d.BeginInvoke(1, 1000, WaitAWhileComplete, d);
12 for (int i = 0; i < 100; i++)
13 {
14 Console.Write("*");
15 Thread.Sleep(50);
16 }
17 }
18
19 static int WaitAWhile(int data, int ms)
20 {
21 Console.WriteLine("WaitAWhile started.");
22 Thread.Sleep(ms);
23 Console.WriteLine("WaitAWhile completed.");
24 return ++data;
25 }
26
27 static void WaitAWhileComplete(IAsyncResult a)
28 {
29 if (a == null)
30 {
31 throw new ArgumentNullException("a");
32 }
33 WaitAWhileDelegate d = a.AsyncState as WaitAWhileDelegate;
34 if (d == null)
35 {
36 throw new Exception("a.AsyncState can not convert to WaitAWhileDelegate");
37 }
38 int result = d.EndInvoke(a);
39 Console.WriteLine("\nresult: {0}", result);
40 }
41 }
注意，第11行代碼BeginInvoke方法中的第4個參數d不可以再為null，否則無法實現回調，即無法執行WaitAWhileComplete函數中第39行的打印輸出功能。
運行結果：
4、可以使用Lamda表達式代替委托。
1 using System;
2 using System.Threading;
3
4 class Program
5 {
6 delegate int WaitAWhileDelegate(int data, int ms);
7
8 static void Main(string[] args)
9 {
10 WaitAWhileDelegate d = new WaitAWhileDelegate(WaitAWhile);
11 d.BeginInvoke(1, 1000, a => { int result = d.EndInvoke(a); Console.WriteLine("\nresult: {0}", result); }, d);
12 for (int i = 0; i < 100; i++)
13 {
14 Console.Write("*");
15 Thread.Sleep(50);
16 }
17 }
18
19 static int WaitAWhile(int data, int ms)
20 {
21 Console.WriteLine("WaitAWhile started.");
22 Thread.Sleep(ms);
23 Console.WriteLine("WaitAWhile completed.");
24 return ++data;
25 }
26 }
運行結果：
