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11.1.2 捕获异常(1)
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11.1.2 捕获异常(1)
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2006-10-13 14:41:00
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<div style='float:left;width:49%'>·<a href='100165372.htm'>10.3 小结</a></div><div style='float:right;width:49%'>·<a href='100165373.htm'>11.1 错误和异常处理</a></div><div style='float:left;width:49%'>·<a href='100165374.htm'>11.1.1 异常类</a></div><div style='float:right;width:49%'>·<a href='100165376.htm'>11.1.2 捕获异常(2)</a></div><div style='float:left;width:49%'>·<a href='100165377.htm'>11.1.3 用户定义的异常类(1)</a></div><div style='float:right;width:49%'>·<a href='100165378.htm'>11.1.3 用户定义的异常类(2)</a></div></div>
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<div id="text"> <link href="css.css" rel="stylesheet" type="text/css" /><h3 style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 0cm; MARGIN-RIGHT: 0cm; FTEL: 8.15pt"><a ftel="_Toc507815038"><span lang="EN-US">11.1.2 </span></a><span style="FONT-FAMILY: 黑体">捕获异常</span></h3>
<p class="MsoNormal"><span lang="EN-US">.NET</span><span style="FONT-FAMILY: 宋体">提供了大量的预定义基类异常对象，该如何在代码中使用它们捕获错误情况？为了在</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">代码中处理可能的错误情况，一般要把程序的相关部分分成</span><span lang="EN-US">3</span><span style="FONT-FAMILY: 宋体">种不同类型的代码块：</span></p>
<p class="1" style="MARGIN-LEFT: 37.55pt; FTEL: -16.1pt"><span lang="EN-US">●<span style="FONT: 7pt 'Times New Roman'"> </span></span><span lang="EN-US">Try</span><span style="FONT-FAMILY: 宋体">块包含的代码组成了程序的正常操作部分，但可能遇到某些严重的错误情况。</span></p>
<p class="1" style="MARGIN-LEFT: 37.55pt; FTEL: -16.1pt"><span lang="EN-US">●<span style="FONT: 7pt 'Times New Roman'"> </span></span><span lang="EN-US">Catch</span><span style="FONT-FAMILY: 宋体">块包含的代码处理各种错误情况，这些错误是</span><span lang="EN-US">try</span><span style="FONT-FAMILY: 宋体">块中的代码执行时遇到的。</span></p>
<p class="1" style="MARGIN-LEFT: 37.55pt; FTEL: -16.1pt"><span lang="EN-US">●<span style="FONT: 7pt 'Times New Roman'"> </span></span><span lang="EN-US" style="LETTER-SPACING: 0.1pt">Finally</span><span style="FONT-FAMILY: 宋体; LETTER-SPACING: 0.1pt">块包含的代码清理资源或执行要在</span><span lang="EN-US" style="LETTER-SPACING: 0.1pt">try</span><span style="FONT-FAMILY: 宋体; LETTER-SPACING: 0.1pt">块或</span><span lang="EN-US" style="LETTER-SPACING: 0.1pt">catch</span><span style="FONT-FAMILY: 宋体; LETTER-SPACING: 0.1pt">块末尾执行的其他操作。无论是否产生异</span><span style="FONT-FAMILY: 宋体">常，都会执行</span><span lang="EN-US">Finally</span><span style="FONT-FAMILY: 宋体">块，理解这一点是非常重要的。因为</span><span lang="EN-US">Finally </span><span style="FONT-FAMILY: 宋体">块包含了应总是执行的清理代码，如果在</span><span lang="EN-US">Finally </span><span style="FONT-FAMILY: 宋体">块中放置了</span><span lang="EN-US">return</span><span style="FONT-FAMILY: 宋体">语句，编译器就会标志一个错误。例如，可以在</span><span lang="EN-US">Finally </span><span style="FONT-FAMILY: 宋体">块中关闭在</span><span lang="EN-US">try</span><span style="FONT-FAMILY: 宋体">块中打开的连接。</span><span lang="EN-US">Finally </span><span style="FONT-FAMILY: 宋体">块是可选的。</span></p>
<p class="MsoNormal"><a ftel="try1"></a><a ftel="catch1"></a><a ftel="finally1"><span style="FONT-FAMILY: 宋体">那么，这些块是如何组合在一起捕获错误情况的？下面就是其步骤：</span></a></p>
<p class="MsoNormal"><span lang="EN-US">(1) </span><span style="FONT-FAMILY: 宋体">程序流进入</span><span lang="EN-US">try</span><span style="FONT-FAMILY: 宋体">块。</span></p>
<p class="MsoNormal"><span lang="EN-US">(2) </span><span style="FONT-FAMILY: 宋体">如果没有错误发生，就会正常执行操作。当程序流离开</span><span lang="EN-US">try</span><span style="FONT-FAMILY: 宋体">块后，即使什么也没有发生，也会自动进入</span><span lang="EN-US">finally</span><span style="FONT-FAMILY: 宋体">块</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">第</span><span lang="EN-US">(5)</span><span style="FONT-FAMILY: 宋体">步</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">。但如果在</span><span lang="EN-US">try</span><span style="FONT-FAMILY: 宋体">块中程序流检测到一个错误，程序流就会跳转到</span><span lang="EN-US">catch</span><span style="FONT-FAMILY: 宋体">块</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">下一步</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">。</span></p>
<p class="MsoNormal"><span lang="EN-US">(3) </span><span style="FONT-FAMILY: 宋体">在</span><span lang="EN-US">catch</span><span style="FONT-FAMILY: 宋体">块中处理错误。</span></p>
<p class="MsoNormal"><span lang="EN-US">(4) </span><span style="FONT-FAMILY: 宋体">在</span><span lang="EN-US">catch</span><span style="FONT-FAMILY: 宋体">块执行完后，程序流会自动进入</span><span lang="EN-US">finally</span><span style="FONT-FAMILY: 宋体">块：</span></p>
<p class="MsoNormal"><span lang="EN-US">(5) </span><span style="FONT-FAMILY: 宋体">执行</span><span lang="EN-US">finally</span><span style="FONT-FAMILY: 宋体">块。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">用于完成这些任务的</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">语法如下所示：</span></p>
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