浅析C#之——Observer, Delegate和event（2）
接下来说一下Delegate
先介绍一下Delegate类：
Delegate——委托，是C#中对于函数指针进行封装后的对象，因为C#和JAVA一样都不允许直接使用指针这种高效但危险的东西，所以就用Delegate对象将其封装了起来以增加其使用的安全性；此外，比起直接使用字段，使用对象会更为方便，因为有了对象的封装后，就可以在对象内部预设需要的方法，为外部的调用增添许多便利。
创建委托时，delegate修饰符使其后类型继承MulticastDelegate，该基类提供委托以赋值，添加委托，移除委托和调用委托方法等操作，具体更多功能可查阅MSDN。
先写一个关于使用Delegate的例子：delegate.cs
using System;// 创建一个delegatedelegate int MyHandler(int d1, int d2); class Test{public static int Add(int x, int y){Console.WriteLine("Add has been invoked..");return x+y;}public int Minus(int x, int y){Console.WriteLine("Minus has been invoked..");return x-y;}public static void Main(){Console.WriteLine("mh1:=====================================");MyHandler mh1 = new MyHandler(Test.Add);//绑定静态方法；Console.WriteLine("Outcome1: "+ mh1(100, 200));//==>mh1.Invoke(100, 200); ==> {jump Test.Add;}Console.WriteLine();Console.WriteLine("mh2:=====================================");Test t = new Test();MyHandler mh2 = new MyHandler(t.Minus);//绑定动态方法，这里其实传了两个参数：t和&Minus；Console.WriteLine("Outcome2: "+ mh2(100, 50));Console.WriteLine();Console.WriteLine("mh3:=====================================");MyHandler mh3 = mh1 + mh2;// ;构建委托链；有序的；Console.WriteLine("Outcome3: "+ mh3(200, 100));//依次执行mh1，mh2；返回值是最后一个委托方法的返回值，在此为mh2的返回值；Console.WriteLine();Console.WriteLine("mh4:=====================================");MyHandler mh4 = mh1 + mh2 + mh3;Delegate[] mhs = mh4.GetInvocationList(); //使用Delegate的GetInvocationList()方法可以数组的形式获得委托链中的每一个委托，从而实现对于委托链的随机访问；Console.WriteLine(mhs);for(int i = 0; i<mhs.Length; i++) //遍历委托链；{MyHandler tempHandler =(MyHandler)mhs[i];Console.WriteLine("outcome4: " + i + " " + tempHandler(200, 100));}Console.WriteLine();Console.WriteLine("mh5:=====================================");MyHandler mh5 = delegate(int x, int y){ //绑定匿名方法；Console.WriteLine("匿名方法：");return x*y;};Console.WriteLine("Outcome5: " + mh5(100,200));}}
class MyHandler : MulticastDelegate{//构造器；public MyHandler(Object object, IntPtr method);//这个方法和源代码指定的原型一样；public virtual void Invoke(int d1, int d2);//以下方法实现了对回调方法的异步回调，具体还没有研究过。。。public virtual IAsyncResult BeginInvoke(...);public irtual void EndInvoke(...);} //MulticastDelegate内最主要的是包含了三个静态字段：class MulticastDelegate{private Object _target; //这个字段用来指出要传给实例方法的隐式参数this的值；//当委托对象包装的是一个静态方法时，这个字段为null；//当委托对象包装一个实例方法时，这个字段引用的是回调函数要操作的对象；private IntPtr _method;//一个内部的整数值，CLR用它标示要回调的方法；可以理解为一个函数指针；private Object _invocationList;//用来指向委托链中的下一个委托对象；//...}Console.WriteLine("mh2:=====================================");Test t = new Test();MyHandler mh2 = new MyHandler(t.Minus);//绑定动态方法，这里其实传了两个参数：t和&Minus；Console.WriteLine("Outcome2: "+ mh2(100, 50));Console.WriteLine();
mh2.Invoke(100,50)
using System;//using System.Collections;interface ReceiveMessage{void storeMessage(String message);}//创建委托类型；delegate void ReceiverList(String message);class MessageCenter{private String messageString; // MessageCenter用来缓存消息的String字段；//private ArrayList receiverList = new ArrayList();private ReceiverList receiverList; //has a delegate；//添加消息接受者；public void addReceiver(ReceiveMessage receiver){//receiverList.Add(receiver);receiverList += new ReceiverList(receiver.storeMessage);}//移除消息接受者；public void removeReceiver(ReceiveMessage receiver){//receiverList.Remove(receiver);receiverList -= new ReceiverList(receiver.storeMessage);}// 新建消息；public void newMessage(String message){Console.WriteLine("New message: " + message + "... [MessageCenter]" );this.messageString = message;}// 通知MessageStore有新消息，将其备份入MessageStore；//public void notice(MessageStore messageStore)/*public void notice(ReceiveMessage messageStore) //将对象参数类型换成接口类型；{//messageStore.MessageString = this.messageString;//Console.WriteLine("Message: '" + messageString + "' have been stored in MessageStore...");messageStore.storeMessage(this.messageString);}*/public void notice()//// 通知所有已注册的receiver有新消息，并调用其storeMessage方法；{/*foreach(Object receiver in receiverList){(receiver as ReceiveMessage).storeMessage(this.messageString);}*/this.receiverList(this.messageString);}}class MessageStore : ReceiveMessage{private String messageString;// MessageStore用户存储消息的String字段；// 其实应该是一个String容器用来存储多条消息，不过在此为了简单只放一条消息;public String MessageString{get{return messageString;}set{this.messageString = value;}}/*public void storeMessage(String message) { this.messageString = message; Console.WriteLine("Message: '" + this.messageString + "' have been stored in MessageStore..."); } */ public void storeMessage(String message) //实现接口方法storeMessage(String message)； { this.messageString = message; Console.WriteLine("Message: '" + this.messageString + "' have been stored in MessageStore..."); }// 列出MessageStore中已存储的消息；public void listMessages(){Console.WriteLine("Stored message1: '" + this.messageString + "'...[MessageStore]");}}class MessageChecker : ReceiveMessage{private String checkResult;public void storeMessage(String message) //实现接口方法storeMessage(String message)；{this.checkResult = "OK!";Console.WriteLine("The message: '" + message + "' has been checked...");}public void showCheckResult(){Console.WriteLine("The checkResule is: " + this.checkResult + " [MEssageChecker]");}}class Test{public static void Main(){MessageCenter messageCenter = new MessageCenter();MessageStore messageStore = new MessageStore();MessageChecker messageChecker = new MessageChecker();messageCenter.addReceiver(messageStore);messageCenter.addReceiver(messageChecker);messageCenter.newMessage("Hello world!"); //新建消息Hello world；//messageCenter.notice(messageStore);//通知messageStore有消息需要存储；messageCenter.notice();messageStore.listMessages();//列出messageStore中已经存储的消息；messageChecker.showCheckResult(); //显示messageChecker的checkResule;}}