场景描述猫和老鼠:猫来了,老鼠跑掉!怎么实现? 实现代码之前实现方式:
1 public class Cat
2 { 3 4 public void ScreamOut(string msg) 5 { 6 mouse.RunAway(); 7 } 8 } 9 public class Mouse 10 { 11 12 public void RunAway() 13 14 15 }
但是如果老鼠繁殖多了,很多老鼠同时都要跑掉,有的向南有的向北,怎么办呢?重写猫的ScreamOut 方法,这样显然不好; 现实中的情况是,每个老鼠听到猫来了这个情况,自己有自己的逃跑方式,于是委托用到了这里,即:委托相当于一个方法 但是它的参数也是一个方法,这就不能用一般的方法那样定义了; 委托实现如下: 猫类:
1 public class Cat
2 {
3 public string Name { get; set; } 4 public delegate void ScreamEventHandler(object sender, ScreamEventArgs e); 5 public event ScreamEventHandler Scream; 6 public virtual void OnScream(ScreamEventArgs e) 7 { 8 if (this.Scream != null) 9 { 10 this.Scream(this, e); 11 } 12 } 13 public void ScreamOut(string msg) 14 { 15 ScreamEventArgs e = new ScreamEventArgs(msg); 16 OnScream(e); 17 } 18 } 鼠类:
1 public class Mouse
2 {
3 public string Name { get; set; } 4 public Mouse(Cat cat) 5 { 6 cat.Scream += new Cat.ScreamEventHandler(cat_Scream); 7 cat.Scream += this.RunAway; 8 } 9 public void RunAway(object sender, ScreamEventArgs e) 10 { 11 Cat c = (Cat)sender; 12 Console.WriteLine("{0} coming,she said:\"{1}\",{2} running!(Running...)", c.Name, e.Msg, this.Name); 13 } 14 void cat_Scream(object sender, ScreamEventArgs e) 15 { 16 Cat c = (Cat)sender; 17 Console.WriteLine("{0} coming,she said:\"{1}\",{2} running!", c.Name, e.Msg, this.Name); 18 } 19 20 } 这里的委托定义和.net Framework 类库定义方式相同,有助于了解系统提供的委托机制,所以还有一个猫叫事件的参数类:
1 public class ScreamEventArgs
2 { 3 public readonly string Msg; 4 public ScreamEventArgs(string msg) 5 { 6 this.Msg = msg; 7 } 8 } 主类调用代码:
1 class Program
2 { 3 static void Main(string[] args) 4 { 5 Cat c1 = new Cat(); 6 c1.Name = "tom"; 7 8 Mouse m1 = new Mouse(c1); 9 m1.Name = "Jearry"; 10 11 Mouse m2 = new Mouse(c1); 12 m2.Name = "Jearry's son"; 13 14 c1.Scream += m2.RunAway; 15 16 c1.ScreamOut("stop"); 17 18 Console.Read(); 19 } 20 } 执行结果:
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来自: 昵称10504424 > 《C#》