C#高级编程：使用XPath命名空间中的类[2]

——此文章摘自《C#高级编程（第版）》定价元 特价元 购买

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如果要把这些书的成本相加该怎么办？XPathNavigator为此包含了Evaluate方法Evaluate有个重载方法第一个包含一个字符串该字符串就是XPath函数调用第二个Evaluate重载方法的参数是XPathExpression对象第三个Evaluate重载方法的参数是XPathExpression 和 XPathNodeIterator如果对示例进行下述修改(这个版本的代码在XPathXSLSample中)

private void button_Click(object sender SystemEventArgs e)

{

//modify to match your path structure

XPathDocument doc = new XPathDocument(\\\\\\booksxpathXML);

//create the XPath navigator

XPathNavigator nav = docCreateNavigator();

//create the XPathNodeIterator of book nodes

// that have genre attribute value of novel

XPathNodeIterator iter = navSelect(/bookstore/book[@genre=novel]);

while(iterMoveNext())

{

LoadBook(iterCurrentClone());

}

//add a break line and calculate the sum

listBoxItemsAdd(========================);

listBoxItemsAdd(Total Cost =

+ navEvaluate(sum(/bookstore/book[@genre=novel]/price)));

}

这次可以看到列表框中书籍的总成本如图所示

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