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<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">在本例中，在枚举中使用一个整数值，来表示一天的每个阶段。现在可以把这些值作为枚举的成员来访问。例如，</span><span lang="EN-US">TimeOfDay.Morning</span><span style="FONT-FAMILY: 宋体">返回数字</span><span lang="EN-US">0</span><span style="FONT-FAMILY: 宋体">。使用这个枚举一般是把合适的值传送给方法，在</span><span lang="EN-US">switch</span><span style="FONT-FAMILY: 宋体">语句中迭代可能的值。</span></p>
<p class="2" style="MARGIN: 8.15pt 0cm 0pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">class EnumExample</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">{</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> public static int Main()</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> WriteGreeting(TimeOfDay.Morning);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> return 0;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> static void WriteGreeting(TimeOfDay timeOfDay)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> switch(timeOfDay)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> case TimeOfDay.Morning:</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> Console.WriteLine("Good morning!");</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> break;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> case TimeOfDay.Afternoon:</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> Console.WriteLine("Good afternoon!");</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> break;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> case TimeOfDay.Evening:</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> Console.WriteLine("Good evening!");</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> break;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> default:</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> Console.WriteLine("Hello!");</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> break;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN: 0cm 0cm 8.15pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">}</span></p>
<p class="MsoNormal"><span></span><span><span style="FONT-FAMILY: 宋体">在</span><span lang="EN-US">C#</span></span><span style="FONT-FAMILY: 宋体">中，枚举的真正强大之处是它们在后台会实例化为派生于基类</span><span lang="EN-US">System.Enum</span><span style="FONT-FAMILY: 宋体">的结构。这表示可以对它们调用方法，执行有用的任务。注意因为</span><span lang="EN-US">.NET Framework</span><span style="FONT-FAMILY: 宋体">的执行方式，在语法上把枚举当做结构是不会有性能损失的。实际上，一旦代码编译好，枚举就成为基本类型，与</span><span lang="EN-US">int</span><span style="FONT-FAMILY: 宋体">和</span><span lang="EN-US">float</span><span style="FONT-FAMILY: 宋体">类似。</span></p>
<p class="MsoNormal"><span><span style="FONT-FAMILY: 宋体">可以获取枚举的字符串表示，例如使用前面的</span><span lang="EN-US">TimeOfDay</span></span><span style="FONT-FAMILY: 宋体">枚举：</span></p>
<p class="2" style="MARGIN: 8.15pt 0cm 0pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">TimeOfDay time = TimeOfDay.Afternoon;</span></p>
<p class="2" style="MARGIN: 0cm 0cm 8.15pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">Console.WriteLine(time.ToString());</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">会得到字符串</span><span lang="EN-US">Afternoon</span><span style="FONT-FAMILY: 宋体">。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">另外，还可以从字符串中获取枚举值：</span></p>
<p class="2" style="MARGIN: 8.15pt 0cm 0pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">TimeOfDay time2 = (TimeOfDay) Enum.Parse(typeof(TimeOfDay), "afternoon", true);</span></p>
<p class="2" style="MARGIN: 0cm 0cm 8.15pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">Console.WriteLine((int)time2);</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">这段代码说明了如何从字符串获取枚举值，并转换为整数。要从字符串中转换，需要使用静态的</span><span lang="EN-US">Enum.Parse()</span><span style="FONT-FAMILY: 宋体">方法，这个方法带</span><span lang="EN-US">3</span><span style="FONT-FAMILY: 宋体">个参数，第一个参数是要使用的枚举类型。其语法是关键字</span><span lang="EN-US">typeof</span><span style="FONT-FAMILY: 宋体">后跟放在括号中的枚举类名。</span><span lang="EN-US">typeof</span><span style="FONT-FAMILY: 宋体">运算符将在第</span><span lang="EN-US">5</span><span style="FONT-FAMILY: 宋体">章详细论述。第二个参数是要转换的字符串，第三个参数是一个</span><span lang="EN-US">bool</span><span style="FONT-FAMILY: 宋体">，指定在进行转换时是否忽略大小写。最后，注意</span><span lang="EN-US">Enum.Parse()</span><span style="FONT-FAMILY: 宋体">方法实际上返回一个对象引用<span style="LETTER-SPACING: -1.2pt">——</span></span><span style="LETTER-SPACING: -1.2pt"> </span><span style="FONT-FAMILY: 宋体">我们需要把这个字符串显式转换为需要的枚举类型</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">这是一个取消装箱操作的例子</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">。对于上面的代码，将返回</span><span lang="EN-US">1</span><span style="FONT-FAMILY: 宋体">，作为一个对象，对应于</span><span lang="EN-US">TimeOfDay.Afternoon</span><span style="FONT-FAMILY: 宋体">的枚举值。在显式转换为</span><span lang="EN-US">int</span><span style="FONT-FAMILY: 宋体">时，会再次生成</span><span lang="EN-US">1</span><span style="FONT-FAMILY: 宋体">。</span></p>
<p class="MsoNormal"><span lang="EN-US">System.Enum</span><span style="FONT-FAMILY: 宋体">上的其他方法可以返回枚举定义中的值的个数、列出值的名称等。详细信息参见</span><span lang="EN-US">MSDN</span><span style="FONT-FAMILY: 宋体">文档。</span></p></div>
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<h1 id="divCurrentNode2" style="color: #b83507; width: 100%; text-align: left; font-size: 12px; padding-left: 2px">当前章节:<a href='100162743.htm'><font color='red'>2.6 枚举</font></a></h1>
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<div style='float:left;width:49%'>·<a href='100162740.htm'>2.3 变量</a></div><div style='float:right;width:49%'>·<a href='100162741.htm'>2.4 预定义数据类型</a></div><div style='float:left;width:49%'>·<a href='100162742.htm'>2.5 流控制</a></div><div style='float:right;width:49%'>·<a href='100162744.htm'>2.7 数组</a></div><div style='float:left;width:49%'>·<a href='100162745.htm'>2.8 命名空间</a></div><div style='float:right;width:49%'>·<a href='100162746.htm'>2.9 Main()方法</a></div></div>
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