Delegate与Event的区别[转]

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

namespace Delegate_vs_Event

{

   class Program

   {

      public delegate string TestDelegate(string input);

      public static TestDelegate myDelegate;

      public static event TestDelegate myEvent;

      static void Main(string[] args)

      {

         ///1.在声明委托和事件的类内部，对于Delegate与Event的实例的初始化和调用操作没有任何区别;

         myDelegate = new TestDelegate(TestEvent);

         myEvent = new TestDelegate(TestEvent);

         myDelegate("Delegate");

         myEvent("Event");

         Subject subject = new Subject();

         Observer ob = new Observer(subject);

         subject.Start();

         Console.Read();

      }

      static string TestEvent(string param)

      {

         Console.WriteLine("Hello " + param);

         return string.Empty;

      }

   }

   class Subject

   {

      public delegate void TestHandleForReg(string param);

      public event TestHandleForReg TestHandleEvent;

      public TestHandleForReg TestHandleDelegate;

      public void Start()

      {

         Console.WriteLine("Call external method result:");

         TestHandleEvent("Start");

         Console.WriteLine();

         ///2.对于Delegate与Event的实例，其订阅(Subscribe,即+=)或取消订阅(Unsubscribe，即-=)的操作没有任何区别;

         TestHandleDelegate += Method_Subject1;

         TestHandleDelegate += Method_Subject2;

         TestHandleDelegate -= Method_Subject2;

         TestHandleEvent += Method_Subject1;

         TestHandleEvent += Method_Subject2;

         TestHandleEvent -= Method_Subject2;

         Console.WriteLine("Call internal method result by [Delegate]  ");

         TestHandleDelegate("Delegate");

         Console.WriteLine();

         Console.WriteLine("Call internal method result by [Event]  ");

         TestHandleEvent("Event");

         Console.WriteLine();

      }

      public void Method_Subject1(string str)

      {

         Console.WriteLine("Method_Subject1");

      }

      public void Method_Subject2(string str)

      {

         Console.WriteLine("Method_Subject2");

      }

      public static string Static_Method_Subject()

      {

         return "Static_Method_Subject";

      }

   }

   class Observer

   {

      public Observer(Subject subject)

      {

         subject.TestHandleEvent += Method_Observer;

         subject.TestHandleDelegate += Method_Observer;

         ///3.Delegate与Event唯一区别就在于以下2点：Event提供了更严格的封装访问控制，其目的是为了防止其他类破坏委托的多播链,故不允许在声明事件的类外初始化或调用.

         ///即除了声明Event的类，其它类只能订阅(Subscribe,即+=)或取消订阅(Unsubscribe，即-=)该Event;

         ///   /*1*/

         ///subject.TestHandleEvent = new Subject.TestHandleForReg(Method_Observer);

         /// subject.TestHandleDelegate = new Subject.TestHandleForReg(Method_Observer);///Error:The event 'Delegate_vs_Event.Subject.TestHandleEvent' can only appear on the left hand side of += or -= (except when used from within the type 'Delegate_vs_Event.Subject')    

         ///    /*2*/

         ///subject.TestHandleDelegate("test");

         /// subject.TestHandleEvent("test");///Error:The event 'Delegate_vs_Event.Subject.TestHandleEvent' can only appear on the left hand side of += or -= (except when used from within the type 'Delegate_vs_Event.Subject')   

      }

      public void Method_Observer(string info)

      {

         Console.WriteLine("Observer's method ["+info+"]");

      }

   }

}

1.在声明委托和事件的类内部，对于Delegate与Event的实例的初始化和调用操作没有任何区别;
2.对于Delegate与Event的实例，其订阅(Subscribe,即+=)或取消订阅(Unsubscribe，即-=)的操作没有任何区别;
3.Delegate与Event唯一区别就在于以下2点：Event提供了更严格的封装访问控制，其目的是为了防止其他类破坏委托的多播链,故不允许在声明事件的类外初始化或调用.即除了声明Event的类，其它类只能订阅(Subscribe,即+=)或取消订阅(Unsubscribe，即-=)该Event;