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<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">Calling SomeFunction...</span></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">i = 0</span></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN: 0cm 0cm 8.15pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">ints[0] = 100</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">注意，</span><span lang="EN-US">i</span><span style="FONT-FAMILY: 宋体">的值保持不变，而在</span><span lang="EN-US">ints</span><span style="FONT-FAMILY: 宋体">中改变的值在原来的数组中也改变了。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">注意字符串是不同的，因为字符串是不能改变的</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">如果改变字符串的值，就会创建一个全新的字符串</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">，所以字符串无法显示一般引用类型的行为方式。在方法调用中，对字符串所作的任何改变都不会影响原来的字符串。这一点将在第</span><span lang="EN-US">8</span><span style="FONT-FAMILY: 宋体">章详细讨论。</span></p>
<p class="MsoNormal"><span lang="EN-US">&nbsp;</span></p>
<p class="a3" style="MARGIN-TOP: 8.15pt; TEXT-INDENT: 21.45pt"><span lang="EN-US">(4)</span><span lang="EN-US" style="FONT-FAMILY: 宋体"> </span><span lang="EN-US">ref</span><span style="FONT-FAMILY: 黑体">参数</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 15pt"><span style="FONT-FAMILY: 宋体">通过值传送变量是默认的情况，也可以迫使值参数通过引用传送给方法。为此，要使用</span><span lang="EN-US">ref</span><span style="FONT-FAMILY: 宋体">关键字。如果把一个参数传递给方法，且这个方法的输入参数前带有</span><span lang="EN-US">ref</span><span style="FONT-FAMILY: 宋体">关键字，则该方法对变量所作的任何改变都会影响原来对象的值：</span></p>
<p class="2" style="MARGIN: 6.5pt 0cm 0pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">static void SomeFunction(int[] ints, ref int i)</span></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">{</span></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">&nbsp;&nbsp; ints[0] = 100;</span></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">&nbsp;&nbsp; i = 100;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; //the change to i will persist after SomeFunction() exits</span></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN: 0cm 0cm 6.5pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">}</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">在调用该方法时，还需要添加</span><span lang="EN-US">ref</span><span style="FONT-FAMILY: 宋体">关键字：</span></p>
<p class="2" style="MARGIN: 6.5pt 0cm 6.5pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">SomeFunction(ints, ref i);</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 15pt"><span style="FONT-FAMILY: 宋体">在</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">中添加</span><span lang="EN-US">ref</span><span style="FONT-FAMILY: 宋体">关键字等同于在</span><span lang="EN-US">C++</span><span style="FONT-FAMILY: 宋体">中使用</span><span lang="EN-US">&amp;</span><span style="FONT-FAMILY: 宋体">语法指定按引用传递参数。但是，</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">在调用方法时要求使用</span><span lang="EN-US">ref</span><span style="FONT-FAMILY: 宋体">关键字，使操作更明确</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">因此有助于防止错误</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">。</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 15pt"><span style="FONT-FAMILY: 宋体">最后，</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">仍要求对传递给方法的参数进行初始化，理解这一点也是非常重要的。在传递给方法之前，无论是按值传递，还是按引用传递，任何变量都必须初始化。</span></p>
<p class="a3" style="MARGIN-TOP: 8.15pt; TEXT-INDENT: 21.45pt"><span lang="EN-US">(5)</span><span lang="EN-US" style="FONT-FAMILY: 宋体"> </span><span lang="EN-US">out</span><span style="FONT-FAMILY: 黑体">关键字</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 15pt"><span><span style="FONT-FAMILY: 宋体">在</span><span lang="EN-US">C</span></span><span style="FONT-FAMILY: 宋体">风格的语言中，函数能从一个例程中输出多个值，这种情况很常见。这是使用输出参数实现的<span style="LETTER-SPACING: -0.5pt">&mdash;&mdash;</span>方法是把输出值赋给通过引用传递给方法的变量。通常，变量通过引用传送的初值是不重要的，这些值会被函数重写，函数甚至从来没有使用过它们。</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 15pt"><span style="FONT-FAMILY: 宋体">如果可以在</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">中使用这种相同的约定，就会非常方便。但</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">要求变量在被引用前必须用一个初值进行初始化。在把输入变量传递给函数前，可以用没有意义的值初始化它们，函数将使用真实、有意义的值初始化它们，这样做是没有必要的，有时甚至会引起混乱。但有一种方法能够简化</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">编译器所坚持的输入参数的初始化。</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 15pt"><span style="FONT-FAMILY: 宋体">编译器使用</span><span lang="EN-US">out</span><span style="FONT-FAMILY: 宋体">关键字来初始化。当在方法的输入参数前面加上</span><span lang="EN-US">out</span><span style="FONT-FAMILY: 宋体">关键字时，传递给该方法的变量可以不被初始值初始化。该变量通过引用被传送，所以在从被调用的方法中返回时，方法对该变量进行的任何改变都会被保留下来。在调用该方法时，还需要使用</span><span lang="EN-US">out</span><span style="FONT-FAMILY: 宋体">关键字，这正如在定义该方法时一样：</span></p>
<p class="2" style="MARGIN: 6.5pt 0cm 0pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">static void SomeFunction(out int i)</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">&nbsp;&nbsp; i = 100;</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">&nbsp;</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">&nbsp;&nbsp; int i; // note how i is declared but not initialized</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">&nbsp;&nbsp; SomeFunction(out i);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">&nbsp;&nbsp; Console.WriteLine(i);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">&nbsp;&nbsp; return 0;</span></p>
<p class="2" style="MARGIN: 0cm 0cm 6.5pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">}</span></p>
<p class="MsoNormal"><span lang="EN-US">out</span><span style="FONT-FAMILY: 宋体">关键字是</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">中的新增内容，在</span><span lang="EN-US">VB</span><span style="FONT-FAMILY: 宋体">和</span><span lang="EN-US">C++</span><span style="FONT-FAMILY: 宋体">中没有对应的关键字，该关键字的引入使</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">更安全，更不容易出错。如果在函数体中没有给</span><span lang="EN-US">out</span><span style="FONT-FAMILY: 宋体">参数分配一个值，那么该方法就不能编译。</span></p>
<p class="a3" style="MARGIN-TOP: 8.15pt; TEXT-INDENT: 21.45pt"><span lang="EN-US">(6) </span><span style="FONT-FAMILY: 黑体">方法的重载</span></p>
<p class="MsoNormal"><span><span lang="EN-US">C#</span></span><span style="FONT-FAMILY: 宋体">支持方法的重载&mdash;&mdash;方法的几个有不同签名</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">名称、参数个数、参数类型</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">的版本，但不<span style="LETTER-SPACING: 0.1pt">支持</span></span><span lang="EN-US" style="LETTER-SPACING: 0.1pt">C++</span><span style="FONT-FAMILY: 宋体; LETTER-SPACING: 0.1pt">或</span><span lang="EN-US" style="LETTER-SPACING: 0.1pt">VB</span><span style="FONT-FAMILY: 宋体; LETTER-SPACING: 0.1pt">中的默认参数。为了重载方法，只需声明同名但参数个数或类型不同的方法即可：</span></p>
<p class="2" style="MARGIN: 8.15pt 0cm 0pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">class ResultDisplayer</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">&nbsp;&nbsp; void DisplayResult(string result)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">&nbsp;&nbsp; {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; // implementation</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">&nbsp;&nbsp; }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">&nbsp;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">&nbsp;&nbsp; void DisplayResult(int result)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">&nbsp;&nbsp; {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; // implementation</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">&nbsp;&nbsp; }</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 style="FONT-FAMILY: 宋体">因为</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">不直接支持可选参数，所以需要使用方法重载来达到此目的：</span></p>
<p class="2" style="MARGIN: 8.15pt 0cm 0pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">class MyClass</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">&nbsp;&nbsp; int DoSomething(int x)&nbsp;&nbsp; // want 2nd parameter with default value 10</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">&nbsp;&nbsp; {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; DoSomething(x, 10);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">&nbsp;&nbsp; }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">&nbsp;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">&nbsp;&nbsp; int DoSomething(int x, int y)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">&nbsp;&nbsp; {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; // implementation</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">&nbsp;&nbsp; }</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 style="FONT-FAMILY: 宋体">在任何语言中，对于方法重载来说，如果调用了错误的重载方法，就有可能出现运行错误。第</span><span lang="EN-US">4</span><span style="FONT-FAMILY: 宋体; LETTER-SPACING: 0.1pt">章将讨论如何使代码避免这些错误。现在，知道</span><span lang="EN-US" style="LETTER-SPACING: 0.1pt">C#</span><span style="FONT-FAMILY: 宋体; LETTER-SPACING: 0.1pt">在重载方法的参数方面有一些小区别即可：</span></p>
<p class="1" style="MARGIN-LEFT: 37.55pt; TEXT-INDENT: -16.1pt"><span lang="EN-US">●<span style="FONT: 7pt 'Times New Roman'">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span></span><span style="FONT-FAMILY: 宋体">两个方法不能仅在返回类型上有区别。</span></p>
<p class="1" style="MARGIN-LEFT: 37.55pt; TEXT-INDENT: -16.1pt"><span lang="EN-US">●<span style="FONT: 7pt 'Times New Roman'">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span></span><span style="FONT-FAMILY: 宋体">两个方法不能仅根据参数是声明为</span><span lang="EN-US">ref</span><span style="FONT-FAMILY: 宋体">还是</span><span lang="EN-US">out</span><span style="FONT-FAMILY: 宋体">来区分。</span></p>
<h4 style="TEXT-INDENT: 21.45pt"><span lang="EN-US">2. </span><span style="FONT-FAMILY: 黑体">属性</span></h4>
<p class="MsoNormal"><span><span style="FONT-FAMILY: 宋体">属性</span><span lang="EN-US">(property)</span></span><span style="FONT-FAMILY: 宋体">不太常见，</span><span lang="EN-US">px </span><span style="FONT-FAMILY: 宋体">的概念是：它是一个方法或一对方法，从在客户机代码来看，它们是一个字段。例如</span><span lang="EN-US">Windows</span><span style="FONT-FAMILY: 宋体">窗体的</span><span lang="EN-US">Height</span><span style="FONT-FAMILY: 宋体">属性。假定有下面的代码：</span></p>
<p class="2" style="MARGIN: 8.15pt 0cm 0pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">// mainForm is of type System.Windows.Form</span></p>