初步学习“C#委托”(2)
一个简单的委托例子:
//定义一个返回值为string的无参数的委托注意这个委托只能引用对象中返回值为string的无参数方法
delegate string MyDelegate();
public class MyClass
{
public string SayHello()
{
return "Hello the world!";
}
}
public class TestMyClass
{
public static void Main(string[] args)
{
MyClass myClass1=new MyClass();
MyDelegate myDelegate1=new MyDelegate(myClass1.SayHello);
//下面就使用myDelegate1代替对象myClass1的SayHello方法
System.Console.WriteLine(myDelegate1());
//输出结果为hello the world! 与调用myClass1.SayHello();效果相同
}
}
delegate void MyDelegate(string s);
public class MyClass
{
public void SayHello(string who)
{
System.Console.WriteLine( who+"hello!");
}
public void SayGoodBye(string who)
{
System.Console.WriteLine( who+"good bye!");
}
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}
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public class TestMyClass
{
public static void Main(string[] args)
{
MyClass myClass1=new MyClass();
MyDelegate myDelegate,myDelegate1;
myDelegate=new MyDelegate(myClass1.SayHello);
myDelegate1=new MyDelegate(myClass1.SayGoodBye);
myDelegate+=myDelegate1;
//这样调用myDeletage就相当于同时调用了myClass1.SayHello和myClass1.SayGoodBye
myDelegate("love.net ");
//执行结果输出love.net hello! love.net good bye!
}
}
//定义一个事件代理(委托)
public delegate void EventHandler(string str);
//定义事件源类
class EventSource
{
//定义委托作为事件源类的成员
public event EventHandler Say;
public void TriggerEvent()
{
if(this.Say!=null)
//因为Say是个委托,所以执行Say方法所做的实际操作由注册到它的事件处理函数决定
Say("A event take place!");
}
}
//测试
class Test
{
public static void Main()
{
EventSource aEventSource=new EventSource();
//注册事件处理函数为MyEvent 显示一串字符类似于this.Click+=new EventHandler(Button1_OnClick);
aEventSource.Say+=new EventHandler(MyEvent);
//此处为演示事件触发过程所以就用程序自动触发
//在图形界面应用程序中,一般由用户触发事件,后由操作系统发送消息并调用处理函数 所以程序员只要注册事件处理函数
//和编写事件处理函数的代码就不用关心了
aEventSource.TriggerEvent();
}
//事件处理函数
public static void MyEvent(string str)
{
System.Console.WriteLine(str);
}
}
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如果委托只有这点功能它就没有什么太大的用处了,委托还有一个非常有用的功能就是定义复合委托对象,只有同样类型的委托才能够复合起来,“ + ”能定义复合委托对象, “- ”从一个复合委托中去掉一个委托对象。
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事件驱动是windows应用程序的重要特征 C#委托就是用于产生事件,事件就是用于在一个组件中监听这个组件的变化。
一个简单的例子:
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