1.了解概念
事件就是当对象或类状态发生改变时,对象或类发出的信息或通知。发出信息的对象或类称为"事件源",对事件进行处理的方法称为"接收者",通常事件源在发出状态改变信息时,它并不知道由哪个事件接收者来处理.这就需要一种管理机制来协调事件源和接收者,C++中通过函数指针来完成的.在C#中事件使用委托来为触发时将调用的方法提供类型安全的封装。
在介绍事件之前我们先来了解几个事件的基本概念和几个重要素:
--事件的本质
-事件是特殊的委托实例
-事件关键字:event
--事件的四个要素:
-定义事件
-激发事件
-监听事件
-执行事件
2.事件分析
在.NET中,很多控件都有相关的事件,如Button的Click事件,它能响应鼠标的单击事件。
--定义事件
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--激发事件:单击鼠标
--监听事件
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--执行事件
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3.简单实例--怎样定义一个完整的事件机制
一.定义委托
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4.实例解说
现在我们需要设计一个电子邮件程序,当收到电子邮件时,希望将该消息转发到传真机(Fax)和手机(CallPhone);
一.我们需要传递消息则需要定义事件传递的消息类吧,定义如下:
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namespace EventEmail
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{
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//事件传递的消息定义
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public class MailMsgEventArgs:EventArgs
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{
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public readonly string from, to, subject, body;
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public MailMsgEventArgs(string from, string to, string subject, string body)
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{
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this.from = from;
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this.to = to;
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this.subject = subject;
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this.body = body;
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}
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}
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}
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二.定义委托及事件
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namespace EventEmail
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{
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//定义一委托
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public delegate void MailMsgEventHandler(object sender,MailMsgEventArgs e);
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public class MailManager
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{
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public event MailMsgEventHandler MailMsg; //委托类型的事件
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protected virtual void OnMailMsg(MailMsgEventArgs e)
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{
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if (this.MailMsg != null)
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{
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MailMsg(this, e);
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}
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}
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//通过事件传递消息
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public void SimulateArrivingMsg(string from, string to, string subject, string body)
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{
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MailMsgEventArgs e = new MailMsgEventArgs(from, to, subject, body);
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OnMailMsg(e);
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}
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}
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}
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三 .传真和手机的定义:
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namespace EventEmail
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{
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/// <summary>
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/// 传真机
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/// </summary>
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public class Fax
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{
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private TextBox _tBox;
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public Fax(MailManager mm, TextBox tBox)
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{
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//监听事件
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//这里的FaxMsg,指的是符合MailMsgEventHandler委托的方法,也就是激发事件后所执行的方法
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mm.MailMsg += new MailMsgEventHandler(FaxMsg);
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_tBox = tBox;
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}
16![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
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private void FaxMsg(Object sender, MailMsgEventArgs e)
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{
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_tBox.Text += string.Format("消息到传真:{4}来自:{0}{4}发到:{1}{4}主题:{2}{4}内容:{3}{4}{4}", e.from, e.to, e.subject, e.body, Environment.NewLine);
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}
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public void Register(MailManager mm)
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{
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mm.MailMsg += new MailMsgEventHandler(FaxMsg);
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}
26![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
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public void UnRegister(MailManager mm)
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{
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//注销事件
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mm.MailMsg -= new MailMsgEventHandler(FaxMsg);
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}
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}
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}
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namespace EventEmail
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{
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/// <summary>
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/// 手机
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/// </summary>
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public class CallPhone
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{
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private TextBox _tBox;
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public CallPhone(MailManager mm, TextBox tBox)
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{
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mm.MailMsg += new MailMsgEventHandler(CellPhoneMsg);
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_tBox = tBox;
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}
14![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
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private void CellPhoneMsg(Object sender, MailMsgEventArgs e)
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{
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_tBox.Text += string.Format("消息到手机:{4}来自:{0}{4}发到:{1}{4}主题:{2}{4}内容:{3}{4}{4}", e.from, e.to, e.subject, e.body,Environment.NewLine);
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}
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public void Register(MailManager mm)
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{
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mm.MailMsg += new MailMsgEventHandler(CellPhoneMsg);
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}
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public void UnRegister(MailManager mm)
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{
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mm.MailMsg -= new MailMsgEventHandler(CellPhoneMsg);
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}
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}
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}
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上面的逻辑处理完毕,下面来看看调用情况:
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namespace EventEmail
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{
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public partial class Form1 : Form
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{
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private Fax fax = null;
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private CallPhone cell = null;
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private MailManager mm = null;
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public Form1()
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{
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InitializeComponent();
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mm = new MailManager();
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fax = new Fax(mm, txtReceiver);
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cell = new CallPhone(mm, txtReceiver);
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}
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private void Form1_Load(object sender, EventArgs e)
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{
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}
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private void btnSend_Click(object sender, EventArgs e)
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{
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mm.SimulateArrivingMsg(txtFrom.Text, txtTo.Text, txtSubject.Text, txtBody.Text);
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}
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private void btnClear_Click(object sender, EventArgs e)
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{
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this.txtReceiver.Text = "";
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}
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}
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}
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5 .事件的意义
--有利于消息的传播
--有利于模块之间的松散耦合
注:什么是松散耦合?
就以上面电子邮件程序为例。
--如果没有事件机制,在发送邮件时,就需要去调用Fax,CellPhone的相关方法;
--采用事件机制,在发送邮件时,仅许激发邮件管理器的事件既可,与Fax和CellPhone无关;
也就是说,邮件管理器和Fax、CellPhone之间的依赖关系被解除了。
本文就简单的介绍于此,上面看不太明白的可下示例程序了解;
示例程序在载:EventDemo.rar
转自:http://www.cnblogs.com/beniao/archive/2008/04/20/1158940.html