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+"]");
      }
   }

}