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<p class="MsoNormal" style="LINE-HEIGHT: 17pt"><span style="FONT-FAMILY: 宋体">目前，我们已经引发了事件，还需要一些代码来处理它。在项目中创建一个新类，在这个例子中把该类称为</span><span lang="EN-US">BusEntity</span><span style="FONT-FAMILY: 宋体">。本项目的目的是检查当前时间的秒数，如果它小于</span><span lang="EN-US">30</span><span style="FONT-FAMILY: 宋体">，就把一个字符串值设置为时间；如果它大于</span><span lang="EN-US">30</span><span style="FONT-FAMILY: 宋体">，就把字符串设置为</span><span lang="EN-US">""</span><span style="FONT-FAMILY: 宋体">，并取消事件。下面是代码：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">using System;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">using System.IO;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">using System.ComponentModel;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">namespace SimpleEvent</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">{</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> public class BusEntity</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> string _time ="";</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> public BusEntity()</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> Form1.Action += new Form1.ActionEventHandler(Form1_Action);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> private void Form1_Action(object sender, ActionCancelEventArgs ev)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> ev.Cancel = !DoAction();</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> if(ev.Cancel)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> ev.Message ="Wasn’t the right time.";</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> private bool DoAction()</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> bool retVal = false;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> DateTime tm = DateTime.Now;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> if(tm.second) < 30)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> _time ="The time is" + DateTime.Now.ToLongTimeString();</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> retVal = true;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> else</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> _time = "";</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> return retVal;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> public string TimeString</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> get {return _time;}</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">}</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 17pt"><span style="FONT-FAMILY: 宋体">在构造函数中声明了</span><span lang="EN-US">Form1.Action</span><span style="FONT-FAMILY: 宋体">事件的处理程序。注意其语法非常类似于前面的</span><span lang="EN-US">Click</span><span style="FONT-FAMILY: 宋体">事件的语法。由于声明事件使用的模式都是相同的，所以语法也应保持一致。还要注意如何获取</span><span lang="EN-US">Action</span><span style="FONT-FAMILY: 宋体">事件的引用，而无需在</span><span lang="EN-US">BusEntity</span><span style="FONT-FAMILY: 宋体">类中有对</span><span lang="EN-US">Form1</span><span style="FONT-FAMILY: 宋体">的引用。在</span><span lang="EN-US">Form1</span><span style="FONT-FAMILY: 宋体">类中，将</span><span lang="EN-US">Action</span><span style="FONT-FAMILY: 宋体">事件声明为静态，这并不是必需的，但这样可以更容易创建处理程序。我们可以把事件声明为</span><span lang="EN-US">public</span><span style="FONT-FAMILY: 宋体">，但接着需要引用</span><span lang="EN-US">Form1</span><span style="FONT-FAMILY: 宋体">的一个实例。</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 17pt"><span style="FONT-FAMILY: 宋体">在构造函数中编写事件时，调用添加到委托列表中的方法</span><span lang="EN-US">Form1_Action</span><span style="FONT-FAMILY: 宋体">，并遵循命名标准。在处理程序中，需要确定是否取消事件。</span><span lang="EN-US">DoActions</span><span style="FONT-FAMILY: 宋体">方法根据前面描述的时间条件返回一个布尔值，并把</span><span lang="EN-US">_time</span><span style="FONT-FAMILY: 宋体">字符串设置为正确的值。</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 17pt"><span style="FONT-FAMILY: 宋体">在</span><span lang="EN-US">DoActions</span><span style="FONT-FAMILY: 宋体">返回值后，就把该值赋给</span><span lang="EN-US">ActionCancelEventArgs</span><span style="FONT-FAMILY: 宋体">的</span><span lang="EN-US">Cancel</span><span style="FONT-FAMILY: 宋体">属性。</span><span lang="EN-US">EventArgs</span><span style="FONT-FAMILY: 宋体">类一般仅在事件发送器和接收器之间来回传递值。如果取消了事件</span><span lang="EN-US">(ev.Cancel = true)</span><span style="FONT-FAMILY: 宋体">，</span><span lang="EN-US">Message</span><span style="FONT-FAMILY: 宋体">属性就设置为一个字符串值，以说明事件为什么被取消。</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 17pt"><span style="FONT-FAMILY: 宋体">如果再次查看</span><span lang="EN-US">btnRaise_Click</span><span style="FONT-FAMILY: 宋体">事件处理程序的代码，就可以看出</span><span lang="EN-US">Cancel</span><span style="FONT-FAMILY: 宋体">属性的使用方式：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">private void btnRaise_Click(object sender, EventArgs e)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">{</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> ActionCancelEventArgs cancelEvent = new ActionCancelEventArgs();</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> OnAction(this, cancelEvent);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> If(cancelEvent.Cancel)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> lblInfo.Text = cancelEvent.Message;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> else</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> lblInfo.Text = _busEntity.TimeString;</span></p>
<p class="2" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">}</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 17pt"><span style="FONT-FAMILY: 宋体">注意创建了</span><span lang="EN-US">ActionCancelEventArgs</span><span style="FONT-FAMILY: 宋体">对象。接着引发了事件</span><span lang="EN-US">Action</span><span style="FONT-FAMILY: 宋体">，并传递了新建的</span><span lang="EN-US">ActionCancelEventArgs</span><span style="FONT-FAMILY: 宋体">对象。在调用</span><span lang="EN-US">OnAction</span><span style="FONT-FAMILY: 宋体">方法，引发事件</span><span lang="EN-US">Action</span><span style="FONT-FAMILY: 宋体">时，</span><span lang="EN-US">BusEntity</span><span style="FONT-FAMILY: 宋体">对象中</span><span lang="EN-US">Action</span><span style="FONT-FAMILY: 宋体">事件处理程序的代码就会执行。如果还有其他对象注册了事件</span><span lang="EN-US">Action</span><span style="FONT-FAMILY: 宋体">，它们也会执行。记住，如果其他对象也处理这个事件，它们就会看到同一个</span><span lang="EN-US">ActionCancelEventArgs</span><span style="FONT-FAMILY: 宋体">对象。如果需要确定是哪个对象取消了事件，而且如果有多个对象取消了事件，就需要在</span><span lang="EN-US">ActionCancelEventArgs</span><span style="FONT-FAMILY: 宋体">类中包含某种基于列表的数据结构。</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 17pt"><span style="FONT-FAMILY: 宋体">在与事件委托一起注册的处理程序执行完毕后，就可以查询</span><span lang="EN-US">ActionCancelEventArgs</span><span style="FONT-FAMILY: 宋体">对象，确定它是否被取消了。如果是，</span><span lang="EN-US">lblInfo</span><span style="FONT-FAMILY: 宋体">就包含</span><span lang="EN-US">Message</span><span style="FONT-FAMILY: 宋体">属性值；如果事件没有被取消，</span><span lang="EN-US">lblInfo</span><span style="FONT-FAMILY: 宋体">就会显示当前时间。</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 17pt"><span style="FONT-FAMILY: 宋体; LETTER-SPACING: -0.1pt">本节这基本上说明了如何利用事件和事件中基于</span><span lang="EN-US" style="LETTER-SPACING: -0.1pt">EventArgs</span><span style="FONT-FAMILY: 宋体; LETTER-SPACING: -0.1pt">的对象，在应用程序中传递信息。</span></p></div>
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