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6.1.3 BubbleSorter示例
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2006-10-13 14:41:00
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<div style='float:left;width:49%'>·<a href='100165336.htm'>6.1 委托</a></div><div style='float:right;width:49%'>·<a href='100165337.htm'>6.1.1 在C#中使用委托</a></div><div style='float:left;width:49%'>·<a href='100165338.htm'>6.1.2 简单的委托示例</a></div><div style='float:right;width:49%'>·<a href='100165340.htm'>6.1.4 多播委托</a></div><div style='float:left;width:49%'>·<a href='100165341.htm'>6.2 事件</a></div><div style='float:right;width:49%'>·<a href='100165342.htm'>6.2.1 从客户的角度讨论事件</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"><span lang="EN-US">6.1.3 BubbleSorter</span><span style="FONT-FAMILY: 黑体">示例</span></h3>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">下面的示例将说明委托的用途。我们要编写一个类</span><span lang="EN-US">BubbleSorter</span><span style="FONT-FAMILY: 宋体">，它执行一个静态方法</span><span lang="EN-US">Sort()</span><span style="FONT-FAMILY: 宋体">，这个方法的第一个参数是一个对象数组，把该数组按照升序重新排列。换言之，假定传递的是</span><span lang="EN-US">int</span><span style="FONT-FAMILY: 宋体">数组：</span><span lang="EN-US">{0, 5, 6, 2, 1}</span><span style="FONT-FAMILY: 宋体">，则返回的结果应是</span><span lang="EN-US">{0, 1, 2, 5, 6}</span><span style="FONT-FAMILY: 宋体">。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">冒泡排序算法非常著名，是一种排序的简单方法。它最适合于一小组数字，因为对于大量的数字</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">超过</span><span lang="EN-US">10</span><span style="FONT-FAMILY: 宋体">个</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">，还有更高效的算法。冒泡排序算法重复遍历数组，比较每一对数字，按照需要交换它们的位置，把最大的数字逐步移动到数组的最后。对于给</span><span lang="EN-US">int</span><span style="FONT-FAMILY: 宋体">排序，进行冒泡排序的方法如下所示：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US"> // Note that this isn't part of the sample</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> for (int i = 0; i < sortArray.Length; i++)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> for (int j = i + 1; j < sortArray.Length; j++)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> if (sortArray[j] < sortArray[i]) // problem with this test</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> int temp = sortArray[i]; // swap ith and jth entries</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> sortArray[i] = sortArray[j];</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> sortArray[j] = temp;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">它非常适合于</span><span lang="EN-US">int</span><span style="FONT-FAMILY: 宋体">，但我们希望</span><span lang="EN-US">Sort()</span><span style="FONT-FAMILY: 宋体">方法可以给任何对象排序。换言之，如果某段客户机代码包含</span><span lang="EN-US">Currency</span><span style="FONT-FAMILY: 宋体">结构数组或其他类和结构，就需要对该数组排序。这样，上面代码中的</span><span lang="EN-US">if(sortArray[j] < sortArray[i])</span><span style="FONT-FAMILY: 宋体">就有问题了，因为它需要比较数组中的两个对象，看看哪一个更大。可以对</span><span lang="EN-US">int</span><span style="FONT-FAMILY: 宋体">进行这样的比较，但如何对直到运行期间才知道或确定的新类进行比较？答案是客户机代码知道类在委托中传递的是什么方法，封装这个方法就可以进行比较。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">定义如下的委托：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US"> delegate bool CompareOp(object lhs, object rhs);</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">给</span><span lang="EN-US">Sort</span><span style="FONT-FAMILY: 宋体">方法指定下述签名：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US"> static public void Sort(object [] sortArray, CompareOp gtMethod)</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">这个方法的文档说明强调，</span><span lang="EN-US">gtMethod</span><span style="FONT-FAMILY: 宋体">必须表示一个静态方法，该方法带有两个参数，如果第二个参数的值“大于”第一个参数</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">换言之，它应放在数组中靠后的位置</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">，就返回</span><span lang="EN-US">true</span><span style="FONT-FAMILY: 宋体">。</span></p>
<p class="a3" style="MARGIN-TOP: 8.15pt; FTEL: 21.45pt"><span style="FONT-FAMILY: 黑体">注意：</span></p>
<p class="a1" style="FTEL: 21.45pt"><span style="FONT-FAMILY: 楷体_GB2312">这里使用的是委托，但也可以使用接口来解决这个问题。</span><span lang="EN-US">.NET</span><span style="FONT-FAMILY: 楷体_GB2312">提供的</span><span lang="EN-US">IComparer</span><span style="FONT-FAMILY: 楷体_GB2312">接口就用于此目的。但是这里使用委托是因为这种问题本身要求使用委托。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">设置完毕后，下面定义类</span><span lang="EN-US">BubbleSorter</span><span style="FONT-FAMILY: 宋体">：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US"> class BubbleSorter</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> static public void Sort(object [] sortArray, CompareOp gtMethod)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> for (int i=0 ; i<sortArray.Length ; i++)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> for (int j=i+1 ; j<sortArray.Length ; j++)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> if (gtMethod(sortArray[j], sortArray[i]))</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> object temp = sortArray[i];</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> sortArray[i] = sortArray[j];</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> sortArray[j] = temp;</span></p>
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