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23.5.1 使用 XmlTextReader类
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23.5.1 使用 XmlTextReader类
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<div style='float:left;width:49%'>·<a href='100165637.htm'>23.3 在.NET中使用MSXML</a></div><div style='float:right;width:49%'>·<a href='100165638.htm'>23.4 使用System.Xml类</a></div><div style='float:left;width:49%'>·<a href='100165639.htm'>23.5 读写流格式的XML</a></div><div style='float:right;width:49%'>·<a href='100165641.htm'>23.5.2 使用XmlValidatingReader类</a></div><div style='float:left;width:49%'>·<a href='100165642.htm'>23.5.3 使用XmlTextWriter类</a></div><div style='float:right;width:49%'>·<a href='100165643.htm'>23.6 在.NET中使用DOM</a></div></div>
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<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="XMLTextReader1"><span lang="EN-US">23.5.1 </span></a><span style="FONT-FAMILY: 黑体">使用</span> <span lang="EN-US">XmlTextReader</span><span style="FONT-FAMILY: 黑体">类</span></h3>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">如前所述，</span><span lang="EN-US">XmlTextReader</span><span style="FONT-FAMILY: 宋体">非常类似于</span><span lang="EN-US">SAX</span><span style="FONT-FAMILY: 宋体">。它们最大的一个区别是</span><span lang="EN-US">SAX</span><span style="FONT-FAMILY: 宋体">是一种推模型</span><span lang="EN-US">(push model)</span><span style="FONT-FAMILY: 宋体">，它把数据拉入应用程序中，开发人员必须接受它，而</span><span lang="EN-US">XmlTextReader</span><span style="FONT-FAMILY: 宋体">是一种拉模型，把应用程序请求的数据拉入该应用程序。这样编程就有一种更简单、更直观的模型。另一个优点是拉模型</span><span lang="EN-US">(pull model)</span><span style="FONT-FAMILY: 宋体">可以选择把什么数据传送到应用程序中。如果不需要所有的数据，就不需要处理它们。而在推模型中，所有的</span><span lang="EN-US">XML</span><span style="FONT-FAMILY: 宋体">数据都必须由应用程序处理，无论是否需要这些数据。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">下面介绍一个非常简单的示例，读取</span><span lang="EN-US">XML</span><span style="FONT-FAMILY: 宋体">数据，再详细介绍</span><span lang="EN-US">XmlTextReader</span><span style="FONT-FAMILY: 宋体">类，这些代码在</span><span lang="EN-US">XmlReaderSample1</span><span style="FONT-FAMILY: 宋体">文件夹中。现在用下面的代码替换前面示例中的命名空间</span><span lang="EN-US">MSXML2</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">using System.Xml;</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">还需要从模块级代码中删除下述代码行：</span></p>
<p class="a6" style="MARGIN-TOP: 4.9pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">private DOMDocument40 doc;</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">下面是按钮的单击事件处理程序：</span></p>
<p class="a6" style="MARGIN-TOP: 4.9pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><a ftel="OLE_LINK24"><span lang="EN-US">protected void button1</span></a><span lang="EN-US" style="FONT-FAMILY: 'Baskerville BE Regular'">_</span><span lang="EN-US">Click (object sender, System.EventArgs e)</span></p>
<p class="a6" 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"> //Modify this path to find books.xml</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> string fileName = "..\\..\\..\\books.xml";</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> //Create the new TextReader Object</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> XmlTextReader tr = new XmlTextReader(fileName);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> //Read in a node at a time</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> while(tr.Read()) </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(tr.NodeType == XmlNodeType.Text)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> listBox1.Items.Add(tr.Value);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="a6" 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">这是</span><span lang="EN-US">XmlTextReader</span><span style="FONT-FAMILY: 宋体">最简单的用法。首先，用</span><span lang="EN-US">XML</span><span style="FONT-FAMILY: 宋体">文件名创建一个字符串对象，再创建一个新的</span><span lang="EN-US">XmlTextReader</span><span style="FONT-FAMILY: 宋体">，其参数为</span><span lang="EN-US">fileName</span><span style="FONT-FAMILY: 宋体">字符串。</span><span lang="EN-US">XmlTextReader</span><span style="FONT-FAMILY: 宋体">目前有</span><span lang="EN-US">13</span><span style="FONT-FAMILY: 宋体">种不同的构造函数重载版本，其参数是字符串</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">文件名和</span><span lang="EN-US">URL)</span><span style="FONT-FAMILY: 宋体">、流和</span><span lang="EN-US">NameTables</span><span style="FONT-FAMILY: 宋体">的不同组合</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">当元素或属性名出现几次后，它们就可以存储到</span><span lang="EN-US">NameTable</span><span style="FONT-FAMILY: 宋体">中，这样比较操作的速度会较快</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">在初始化一个</span><span lang="EN-US">XmlTextReader</span><span style="FONT-FAMILY: 宋体">对象后，没有选择任何节点。只有在此时，才没有当前节点。在开始</span><span lang="EN-US">tr.Read()</span><span style="FONT-FAMILY: 宋体">循环后，第一个</span><span lang="EN-US">Read()</span><span style="FONT-FAMILY: 宋体">会进入文档中的第一个节点，这个节点一般是</span><span lang="EN-US">XML </span><span style="FONT-FAMILY: 宋体">声明节点。在本示例，当进入每个节点时，可比较</span><span lang="EN-US">tr.NodeType </span><span style="FONT-FAMILY: 宋体">和</span><span lang="EN-US">XmlNodeType</span><span style="FONT-FAMILY: 宋体">枚举，找到一个文本节点后，把该文本值添加到列表框，图</span><span lang="EN-US">23-3</span><span style="FONT-FAMILY: 宋体">是加载该列表框后的屏幕图。</span></p>
<p align="center"><span lang="EN-US"><img height="194" src="23/image003.jpg" width="178" border="0" alt="" /></span></p>
<p style="FTEL: .0001pt" align="center"><span style="FONT-FAMILY: 宋体">图</span><span lang="EN-US"> 23-3</span></p>
<h4 style="FTEL: 21.45pt"><span lang="EN-US">1.</span><span lang="EN-US" style="FONT-FAMILY: 宋体"> </span><span lang="EN-US">Read</span><span style="FONT-FAMILY: 黑体">方法</span></h4>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">遍历文档有几种方式，如前面的示例所示，</span><span lang="EN-US">Read()</span><span style="FONT-FAMILY: 宋体">可以进入下一个节点。然后查看该节点是否有一个值</span><span lang="EN-US">(HasValue())</span><span style="FONT-FAMILY: 宋体">、该节点是否有属性</span><span lang="EN-US">(HasAttributes())</span><span style="FONT-FAMILY: 宋体">。也可以使用</span><span lang="EN-US">ReadStartElement()</span><span style="FONT-FAMILY: 宋体">方法，查看当前节点是否是起始元素，如果是起始元素，就可以定位到下一个节点上。如果不是起始元素，就引发一个</span><span lang="EN-US">XmlException</span><span style="FONT-FAMILY: 宋体">。调用这个方法与调用</span><span lang="EN-US">Read ()</span><span style="FONT-FAMILY: 宋体">后再调用</span><span lang="EN-US">IsStartElement</span><span style="FONT-FAMILY: 宋体">是一样的。</span></p>
<p class="MsoNormal"><span lang="EN-US">ReadString() </span><span style="FONT-FAMILY: 宋体">和</span> <span lang="EN-US">ReadChars()</span><span style="FONT-FAMILY: 宋体">方法都可以从元素中读取文本数据。</span><span lang="EN-US">ReadString()</span><span style="FONT-FAMILY: 宋体">返回一个包含数据的字符串对象，而</span><span lang="EN-US">ReadChars()</span><span style="FONT-FAMILY: 宋体">把数据读入字符数组。</span></p>
<p class="MsoNormal"><span lang="EN-US">ReadElementString() </span><span style="FONT-FAMILY: 宋体">类似于</span><span lang="EN-US">ReadString()</span><span style="FONT-FAMILY: 宋体">，但可以把元素名作为参数。如果下一个</span><span lang="EN-US">Content</span><span style="FONT-FAMILY: 宋体">节点不是起始标记，或者</span><span lang="EN-US">Name</span><span style="FONT-FAMILY: 宋体">属性不匹配当前的节点</span><span lang="EN-US">Name</span><span style="FONT-FAMILY: 宋体">，就会引发异常。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">下面的示例说明了如何使用</span><span lang="EN-US">ReadElementString()(</span><span style="FONT-FAMILY: 宋体">这段代码在</span><span lang="EN-US">XmlReaderSample2</span><span style="FONT-FAMILY: 宋体">文件夹中</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">。注意这个示例使用</span><span lang="EN-US">FileStream</span><span style="FONT-FAMILY: 宋体">，所以需要通过</span><span lang="EN-US">using</span><span style="FONT-FAMILY: 宋体">语句来包括</span><span lang="EN-US">System.IO</span><span style="FONT-FAMILY: 宋体">命名空间：</span></p>
<p class="a6" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><a ftel="ReadElementString"><span lang="EN-US">protected void button1</span></a><span lang="EN-US" style="FONT-FAMILY: 'Baskerville BE Regular'">_</span><span lang="EN-US">Click (object sender, System.EventArgs e)</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">{</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US"> //use a filestream to get the data</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> FileStream fs = new FileStream("..\\..\\..\\books.xml", FileMode.Open);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> XmlTextReader tr = new XmlTextReader(fs);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> while(!tr.EOF)</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 we hit an element type, try and load it in the listbox</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> if(tr.MoveToContent() == XmlNodeType.Element && tr.FTEL=="title")</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"> listBox1.Items.Add(tr.ReadElementString());</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
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