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13.3.2 语言无关性(2)
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2006-10-13 14:41:00
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<div style='float:left;width:49%'>·<a href='100165402.htm'>13.3 跨语言支持</a></div><div style='float:right;width:49%'>·<a href='100165403.htm'>13.3.1 CTS和CLS</a></div><div style='float:left;width:49%'>·<a href='100165404.htm'>13.3.2 语言无关性(1)</a></div><div style='float:right;width:49%'>·<a href='100165406.htm'>13.3.3 CLS要求</a></div><div style='float:left;width:49%'>·<a href='100165407.htm'>13.4 全局程序集缓存</a></div><div style='float:right;width:49%'>·<a href='100165408.htm'>13.4.1 本机图像生成器</a></div></div>
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<div id="text"> <link href="css.css" rel="stylesheet" type="text/css" /><h4><span lang="ES">2. </span><span style="FONT-FAMILY: 黑体">编写</span><span lang="ES">VB.NET</span><span style="FONT-FAMILY: 黑体">类</span><span lang="ES"> </span></h4>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">下面使用</span><span lang="EN-US">VB.NET</span><span style="FONT-FAMILY: 宋体">创建一个类。这次仍使用</span><span lang="EN-US">Class Library</span><span style="FONT-FAMILY: 宋体">向导；该项目叫作</span><span lang="EN-US">HelloVB</span><span style="FONT-FAMILY: 宋体">，如图</span><span lang="EN-US">13-19</span><span style="FONT-FAMILY: 宋体">所示。</span></p>
<p align="center"><span lang="EN-US" style="FONT-SIZE: 7pt"><img height="246" src="13/image029.jpg" width="361" alt="" /></span></p>
<p style="FTEL: 8.15pt" align="center"><span style="FONT-FAMILY: 宋体">图</span><span lang="EN-US"> 13-19</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">类的命名空间应改为</span><span lang="EN-US">Wrox.ProCSharp.Assemblies.CrossLanguage</span><span style="FONT-FAMILY: 宋体">。在</span><span lang="EN-US">VB.NET</span><span style="FONT-FAMILY: 宋体">项目中，在项目属性中通过改变项目的根命名空间，就可以改变类的命名空间，如图</span><span lang="EN-US">13-20</span><span style="FONT-FAMILY: 宋体">所示。</span></p>
<p align="center"><span lang="EN-US" style="FONT-SIZE: 7pt"><img height="274" src="13/image030.jpg" width="421" alt="" /></span></p>
<p style="FTEL: 8.15pt" align="center"><span style="FONT-FAMILY: 宋体">图</span><span lang="EN-US"> 13-20</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">要从</span><span lang="EN-US">HelloMCPP</span><span style="FONT-FAMILY: 宋体">中派生类，需要引用</span><span lang="EN-US">HelloMCPP.dll</span><span style="FONT-FAMILY: 宋体">。使用</span><span lang="EN-US">Project | Add Reference</span><span style="FONT-FAMILY: 宋体">就可以把引用添加到</span><span lang="EN-US">C++</span><span style="FONT-FAMILY: 宋体">项目中。在建立程序集时，该引用可以在清单</span><span lang="EN-US">.assembly extern HelloMCPP</span><span style="FONT-FAMILY: 宋体">中看到，如图</span><span lang="EN-US">13-21</span><span style="FONT-FAMILY: 宋体">所示。给项目添加引用，就是把引用的程序集复制到</span><span lang="EN-US">VB.NET</span><span style="FONT-FAMILY: 宋体">项目的输出目录上，所以以后对原引用程序集的改变就是独立的。</span></p>
<p align="center"><span lang="EN-US"><img height="307" src="13/image031.jpg" width="431" alt="" /></span></p>
<p style="FTEL: 8.15pt" align="center"><span style="FONT-FAMILY: 宋体">图</span><span lang="EN-US"> 13-21</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">使用下面的代码创建类</span><span lang="EN-US">HelloVB</span><span style="FONT-FAMILY: 宋体">。类</span><span lang="EN-US">HelloVB</span><span style="FONT-FAMILY: 宋体">继承于</span><span lang="EN-US">HelloMCPP</span><span style="FONT-FAMILY: 宋体">。</span><span lang="EN-US">VB.NET</span><span style="FONT-FAMILY: 宋体">使用关键字</span><span lang="EN-US">Inherits</span><span style="FONT-FAMILY: 宋体">派生于一个基类。</span><span lang="EN-US">Inherits</span><span style="FONT-FAMILY: 宋体">必须在</span><span lang="EN-US">Class</span><span style="FONT-FAMILY: 宋体">语句的后面。基类中的</span><span lang="EN-US">Hello()</span><span style="FONT-FAMILY: 宋体">方法被重写。</span><span lang="EN-US">VB.NET</span><span style="FONT-FAMILY: 宋体">关键字</span><span lang="EN-US">Overrides</span><span style="FONT-FAMILY: 宋体">与</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">关键字</span><span lang="EN-US">override </span><span style="FONT-FAMILY: 宋体">的作用相同。在</span><span lang="EN-US">Hello()</span><span style="FONT-FAMILY: 宋体">方法的执行方式中，使用</span><span lang="EN-US">VB.NET</span><span style="FONT-FAMILY: 宋体">关键字</span><span lang="EN-US">MyBase </span><span style="FONT-FAMILY: 宋体">来调用基类中的</span><span lang="EN-US">Hello()</span><span style="FONT-FAMILY: 宋体">方法。</span><span lang="EN-US">VB.NET</span><span style="FONT-FAMILY: 宋体">关键字</span><span lang="EN-US">MyBase</span><span style="FONT-FAMILY: 宋体">与</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">关键字</span><span lang="EN-US">base</span><span style="FONT-FAMILY: 宋体">的作用相同。执行方法</span><span lang="EN-US">Add()</span><span style="FONT-FAMILY: 宋体">，检查生成的</span><span lang="EN-US">MSIL</span><span style="FONT-FAMILY: 宋体">代码，以查看</span><span lang="EN-US">VB.NET </span><span style="FONT-FAMILY: 宋体">是如何处理数字的。基类中的方法</span><span lang="EN-US">Add()</span><span style="FONT-FAMILY: 宋体">不是虚拟的，所以不能重写。</span><span lang="EN-US">VB.NET </span><span style="FONT-FAMILY: 宋体">关键字</span><span lang="EN-US">Shadows</span><span style="FONT-FAMILY: 宋体">可以隐藏基类的方法，它类似于</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">中的</span><span lang="EN-US">new</span><span style="FONT-FAMILY: 宋体">修饰符，第</span><span lang="EN-US">4</span><span style="FONT-FAMILY: 宋体">章介绍了</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">中的</span><span lang="EN-US">new</span><span style="FONT-FAMILY: 宋体">修饰符：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt"><span lang="ES">Public Class HelloVB</span></p>
<p class="2"><span lang="ES"> Inherits HelloMCPP</span></p>
<p class="2"><span lang="ES"> </span></p>
<p class="2"><span lang="ES"> Public Overrides Sub Hello()</span></p>
<p class="2"><span lang="ES"> MyBase.Hello() </span></p>
<p class="2"><span lang="ES"> Console.WriteLine("Hello, VB.NET") </span></p>
<p class="2"><span lang="ES"> End Sub</span></p>
<p class="2"><span lang="ES"> </span></p>
<p class="2"><span lang="ES"> Public Shadows Function Add(ByVal val1 As Integer, </span><span lang="ES" style="FONT-FAMILY: 'Baskerville BE Regular'">_</span></p>
<p class="2"><span lang="ES"> ByVal val2 As Integer) As Integer</span></p>
<p class="2"><span lang="ES"> Return val1 + val2</span></p>
<p class="2"><span lang="ES"> End Function</span></p>
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