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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8" /><title>Hyperlinked ECMA C# Language Specification</title><meta name="author" content="Jon Jagger" /><link rel="stylesheet" href="ecma334.css"></link></head><body><div align="right"><em><a href="http://www.jaggersoft.com">Jon Jagger</a></em></div><div align="right"><a href="mailto:jon@jaggersoft.com">jon@jaggersoft.com</a></div><form method="get" action="http://search.atomz.com/search/"><input size="30" name="sp-q"></input><input type="submit" value="Search C# Spec"></input><input type="hidden" name="sp-a" value="sp10024177"></input><input type="hidden" name="sp-f" value="ISO-8859-1"></input></form><a href="toc.htm">Table of Contents</a> <a href="1.htm">1</a> <a href="2.htm">2</a> <a href="3.htm">3</a> <a href="4.htm">4</a> <a href="5.htm">5</a> <a href="6.htm">6</a> <a href="7.htm">7</a> <a href="8.htm">8</a> <a href="9.htm">9</a> <a href="10.htm">10</a> <a href="11.htm">11</a> <a href="12.htm">12</a> <a href="13.htm">13</a> <a href="14.htm">14</a> <a href="15.htm">15</a> <a href="16.htm">16</a> <a href="17.htm">17</a> <a href="18.htm">18</a> <a href="19.htm">19</a> <a href="20.htm">20</a> <a href="21.htm">21</a> <a href="22.htm">22</a> <a href="23.htm">23</a> <a href="24.htm">24</a> <a href="25.htm">25</a> <a href="notes.htm">Notes</a> <a href="HyperlinkedCSharpECMA.zip">Download</a><span class="ruler"></span><span class="heading">ECMA-334 C# Language Specification</span><span class="navigate"><a href="8.7.4.htm"><img src="previous.gif" alt="previous" border="0" /></a><a href="8.7.6.htm"><img src="next.gif" alt="next" border="0" /></a></span><span class="clause-depth"><a href="7.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="9.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="8.htm">8</a></span><span class="clause-title-previous"> Language Overview</span></span><span class="clause-depth"><a href="8.6.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="8.8.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="8.7.htm">8.7</a></span><span class="clause-title-previous"> Classes</span></span><span class="clause-depth"><a href="8.7.4.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="8.7.6.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number">8.7.5</span><span class="clause-title"> Events</span></span><span class="informative"><span class="paragraph">An event is a member that enables an object or class to provide notifications. A class defines an event by providing an event declaration (which resembles a field declaration, though with an added event keyword) and an optional set of event accessors. The type of this declaration must be a delegate type. </span><span class="paragraph">An instance of a delegate type encapsulates one or more callable entities. For instance methods, a callable entity consists of an instance and a method on that instance. For static methods, a callable entity consists of just a method. Given a delegate instance and an appropriate set of arguments, one can invoke all of that delegate instance's methods with that set of arguments. </span><span class="paragraph">In the example <pre class="code-example">
public delegate void EventHandler(object sender, System.EventArgs e);
public class Button
{
public event EventHandler Click;
public void Reset() {
Click = null;
}
}
</pre>the Button class defines a Click event of type EventHandler. Inside the Button class, the Click member is exactly like a private field of type EventHandler. However, outside the Button class, the Click member can only be used on the left-hand side of the += and -= operators. The += operator adds a handler for the event, and the -= operator removes a handler for the event. The example <pre class="code-example">
using System;
public class Form1
{
public Form1() {
// Add Button1_Click as an event handler for Button1's Click event
Button1.Click += new EventHandler(Button1_Click);
}
Button Button1 = new Button();
void Button1_Click(object sender, EventArgs e) {
Console.WriteLine("Button1 was clicked!");
}
public void Disconnect() {
Button1.Click -= new EventHandler(Button1_Click);
}
}
</pre>shows a Form1 class that adds Button1_Click as an event handler for Button1's Click event. In the Disconnect method, that event handler is removed. </span><span class="paragraph">For a simple event declaration such as <pre class="code-example">
public event EventHandler Click;
</pre>the compiler automatically provides the implementation underlying the += and -= operators. </span><span class="paragraph">An implementer who wants more control can get it by explicitly providing add and remove accessors. For example, the Button class could be rewritten as follows: <pre class="code-example">
public class Button
{
private EventHandler handler;
public event EventHandler Click {
add { handler += value; }
remove { handler -= value; }
}
}
</pre></span><span class="paragraph">This change has no effect on client code, but allows the Button class more implementation flexibility. For example, the event handler for Click need not be represented by a field. </span></span><span class="ruler"></span><table><tr><td><table align="left" bgcolor="navy"><tr bgcolor="navy"><td><font face="Arial,sans-serif" size="6" color="yellow"><strong>{ JSL }</strong></font></td></tr></table></td></tr><tr><td><font face="Arial,sans-serif" size="2" color="navy"><strong>Jagger Software Ltd</strong></font></td></tr><tr><td><font face="Arial,sans-serif" size="2" color="navy"><strong>Company # 4070126</strong></font></td></tr><tr><td><font face="Arial,sans-serif" size="2" color="navy"><strong>VAT # 762 5213 42</strong></font></td></tr></table><img src="valid-html401.png" align="left" height="31" width="88" alt="Valid HTML 4.01" /><img src="vcss.gif" align="left" height="31" width="88" alt="Valid CSS" /></body></html>⌨️ 快捷键说明
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