后来发现Delegate比起接口可以"乱用".因为它只要方法的签名一样就可以替换.比如下面这个例子.
public class Client 
{ 
public dalegate int AddHandle(int a, int b); public AddHandle Add ; public void Do() 
{ // Add(2,3); 
} 
} public class Math { publicint Add(int a,int b) { return a+b; } publicint Sub(int a,int b) { return a-b; } } 这下可好,如果象下面这样用,结果岂不变成-1了
Client c = new Client(); c.Add = new Client.AddHandle( new Math().Sub); c.Do(); 如果用接口,约束性就强了点.
public class Client { public AddHandle iadder; publicvoid Do() { // iadder.Add(); } } public interface AddHandle { int Add(int a, int b); } public class Client { public AddHandle Add; } public class Math : AddHandle { publicint Add(int a, int b) { return a + b; } publicint Sub(int a, int b) { return a - b; } } Client c = new Client(); c.iadder = new Math(); c.Do(); 这样不太可能出上面那样的错误. 不过Delegate这么灵活也不全是错.
如果Math中的方法是Static的(也是很有可能的),那接口就傻眼了,但是Delegate照样能搞定. 根据Delegate的这个灵活的特点,我想了一个合理的应用---计算工资. public delegate double OperationHandle( double a, double b); public class Math { publicint Add(int a,int b) { return a+b; } publicint Sub(int a,int b) { return a-b; } } private int wage = 0 ; public void ModifyWage( int value,OperationHandle operation) { int newWage= operation(wage, value); wage= newWage; } 加加减减,甚至乘除,只要绑定上不同的operation就ok了,这样岂不是很方便? 如果用接口实现呢?
public interface OperationHandle { int Execute(int a, int b); } public class Add : OperationHandle { publicint Execute(int a, int b) { return a + b; } } public class Sub: OperationHandle { publicint Execute(int a, int b) { return a - b; } } private int wage = 0 ; public void ModifyWage( int value,OperationHandle operation) { int newWage= operation.Execute(wage, value); wage= newWage; } 可以看出这就是Command模式. 还有好玩的,Delegate不是可以使用多播嘛(+=),用在这里就更好玩了.
public delegate int OperationHandle( int a, int b); public class Math { publicint Add(int a,int b) { return a+b; } publicint Sub(int a,int b) { return a-b; } } private int wage = 0 ; public void ModifyWage( int [] value,OperationHandle operation) { int i=0; foreach(OperationHandle oh in operation.GetInvokeList()) { int newWage= oh(wage, value[i]); wage+= newWage; i++; } } 很方便吧,接口也能做.Command加上Composition,不过要想变换参数似乎有点困难,(这仅仅是个例子,不考虑那么多了)
public class Composite : OperationHandle { IList operations =new ArrayList(); publicint Execute(int a, int b) { int result =0; foreach(Operation o in operations) result += o.Execute(a, b); return result; } publicvoid AddOperation(Operation o) { operations.Add(o); } } 看完这些你感觉怎么样?难怪有人说.net的架构师是Delegate先生,delegate做的事,interface
基本上都能做,不过delegate是带来了不少方便,不过初学者比较难理解delegate这个概念,而且如前文所说 delegate在带来灵活性的同时也带来了一定的危险.