委托学习(2)

  1 using System;
  2 using System.Collections.Generic;
  3 using System.Linq;
  4 using System.Text;
  5 using System.Threading.Tasks;
  6 
  7 namespace Delegate2
  8 {
  9     //声明委托
 10     public delegate void PrintHandler(string message);
 11 
 12     //定义类1的委托方法;
 13     public class PrintProvider1
 14     {
 15         public void Print(string msg)
 16         {
 17             Console.WriteLine("++++++1"+msg.ToString()+"++++++");
 18         }
 19     }
 20     //定义类2的委托方法;
 21     public class PrintProvider2
 22     {
 23         public void Prinit(string msg)
 24         {
 25             Console.WriteLine("------2"+msg.ToString()+"-------");
 26         }
 27     }
 28 
 29     class Test
 30     {
 31         //静态被委托的方法
 32         static void StaticPrint(string msg)
 33         {
 34             Console.WriteLine("######3"+msg.ToString()+"######");
 35         }
 36 
 37         static void Main(string[] args)
 38         {
 39             string s = "委托链";
 40 
 41             //实例两个PrintProvider类的对象
 42             PrintProvider1 pp1 = new PrintProvider1();
 43             PrintProvider2 pp2 = new PrintProvider2();
 44 
 45             //委托对象1的实例
 46             PrintHandler prn1 = new PrintHandler(pp1.Print);
 47             Console.WriteLine("\n委托实例1打印的结果:");
 48             prn1(s);
 49 
 50             //委托对象2的实例
 51             PrintHandler prn2 = new PrintHandler(pp2.Prinit);
 52             Console.WriteLine("\n委托实例2打印的结果:");
 53             prn2(s);
 54 
 55             //委托对象3的实例
 56             PrintHandler prn3 = new PrintHandler(Test.StaticPrint);
 57             Console.WriteLine("\n委托实例3打印的结果:");
 58             prn3(s);
 59 
 60             //委托链的增加
 61             Console.WriteLine("\n委托实例prn+prn2的结果:");
 62             PrintHandler prn = prn1 + prn2;
 63             prn(s);
 64 
 65             Console.WriteLine("\n委托实例prn+prn2+prn3的结果:");
 66             prn += prn3;
 67             prn(s);
 68 
 69             //委托的移除
 70             Console.WriteLine("\n委托实例prn1+prn3");
 71             prn -= prn2;
 72             prn(s);
 73 
 74             Console.WriteLine("\n委托实例prn3");
 75             prn -= prn1;
 76             prn(s);
 77 
 78             Console.WriteLine("\n试图调用空的委托链引发异常");
 79             try
 80             {
 81                 //委托移除
 82                 //prn = (PrintHandler)Delegate.Remove(prn, new PrintHandler(pp1.Print));
 83                 prn -= prn3;
 84                 prn(s);
 85             }
 86             catch (NullReferenceException ex)
 87             {
 88                 Console.WriteLine(ex.Message);
 89             }
 90 
 91             Console.WriteLine("\n试图从null的委托链移除委托，无效");
 92             try
 93             {
 94                 prn -= prn;
 95                 prn(s);
 96             }
 97             catch(NullReferenceException ex)
 98             {
 99                 Console.WriteLine(ex.Message);
100             }
101 
102             Console.ReadLine();
103         }
104 
105     }
106 }