entityMap|0|type|LINK|mutability|MUTABLE|data|url|https://adared.ch/qdomnodemodel-qxmlquery|1|https://www.qtcentre.org/threads/37645-QAbstractXmlNodeModel-implementation-QDomNodeModel-QXmlQuery|blocks|key|4ojed|text|下面是我用来通过XPath表达式在QDomDocument中搜索节点的实用函数。它使用@Alejandro建议的QDomNodeModel类，可从https://adared.ch/qdomnodemodel-qxmlquery下载。它基于https://www.qtcentre.org/threads/37645-QAbstractXmlNodeModel-implementation-QDomNodeModel-QXmlQuery中的用法示例。感谢Stanislaw+Adaszewski，他提供了QDomNodeModel类和用法示例。|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|7v6d5|QDomNodeModel中有一些方法被注释为未实现。但是，对于我需要搜索的简单XML内容，QDomNodeModel就足够了。|43o9i|//
///+@brief+Search+for+nodes+in+a+QDomDocument+using+an+XPath.
///+@note+I+cannot+return+a+QDomNodeList,+because+it+has+no+public+methods+for+adding+items+to+it.
///+@param[in]+doc+The+document+to+search.
///+@param[in]+fromNode+The+node+in+the+document+to+start+searching+from.
///+++e.g.,+to+search+the+whole+document,+use+<code>doc.documentElement()</code>.
///+@param[in]+xpath+The+XPath+expression.
///+@return+A+list+of+found+nodes.
//
QList<QDomNode>+findNodes(+QDomDocument+const+&+doc,+QDomNode+const+&+fromNode,+QString+const+&+xpath+)
{
++qDebug(+"%25s",+__FUNCTION__+);
++QList<QDomNode>+foundNodes;

++//------------------------------
++//+The+name+pool+that+everybody+shares.
++QXmlNamePool+pool;

++//------------------------------
++//+The+model+that+wraps+the+document.
++QDomNodeModel+model(+pool,+doc+);

++//------------------------------
++//+The+query.
++//+XQuery10+means+the+default+XQuery+1.0+language,+as+opposed+to+XSLT20.
++QXmlQuery+query(+/*QXmlQuery::XQuery10,*/+pool+);

++//+Operate+on+the+given+node.
++QXmlNodeModelIndex+fromIndex+=+model.fromDomNode(+fromNode+);
++query.setFocus(+QXmlItem(+fromIndex+)+);

++//+The+query+statement.
++query.setQuery(+xpath+);
++if+(+!query.isValid()+)
++{
++++qDebug(+"Query+is+not+valid"+);
++++return+foundNodes;
++}

++//------------------------------
++//+The+destination+for+the+result+of+the+query.
++QXmlResultItems+result;

++//------------------------------
++//+Evaluate+the+query.
++query.evaluateTo(+&result+);
++if+(+result.hasError()+)
++{
++++qDebug(+"Query+evaluation+failed"+);
++++return+foundNodes;
++}

++//------------------------------
++//+The+result+of+the+query.
++qDebug(+"Query+result:"+);
++while+(+!result.next().isNull()+)
++{
++++QXmlNodeModelIndex+index+=+result.current().toNodeModelIndex();
++++QDomNode+node+=+model.toDomNode(+index+);
++++qDebug(+"++%25d+%25s:+%25s",+node.nodeType(),+qPrintable(+node.nodeName()+),+qPrintable(+node.nodeValue()+)+);
++++foundNodes+<<+node;
++}

++return+foundNodes;
}|code-block|syntax|javascript|4epp8|在我的应用程序中，我加载了一个XML文件，并使用上面的实用程序函数对其进行搜索。|28r2e|//------------------------------
//+The+path+of+the+XML+file.
QString+path+=+"settings.xml";

//------------------------------
//+Open+the+file.
QFile+file(+path+);
if+(+!file.open(+QIODevice::ReadOnly+)+)
{
++qDebug(+"Failed+to+open+'%25s':+%25s",+qPrintable(+path+),+qPrintable(+file.errorString()+)+);
++return;
}

//------------------------------
//+Load+the+file+into+a+document.
QDomDocument+doc;
QString+error;
int+line;
int+column;
if+(+!doc.setContent(+&file,+&error,+&line,+&column+)+)
{
++qDebug(+"%25s(%25d,%25d):+%25s",+qPrintable(+path+),+line,+column,+qPrintable(+error+)+);
++return;
}

//------------------------------
//+The+document+root+element.
QDomElement+rootElem+=+doc.documentElement();

//------------------------------
//+Search+for+an+element+whose+name+attribute+has+a+certain+value.
QString+name+=+"Alice";
QString+xpath+=+QString(+"setting[@name='%251']"+).arg(+name+);
QList<QDomNode>+foundNodes+=+findNodes(+doc,+rootElem,+xpath+);

//------------------------------
//+Did+I+find+it?
if+(+foundNodes.size()+>+0+)
{
++QDomElement+foundElem+=+foundNodes.at(+0+).toElement();

++//+Do+something+with+that+element.++++++
++...
}+|dhbt7|要搜索的示例XML内容。|15a0j|<?xml+version='1.0'?>
<settings>
++<setting+name="Bob">12</setting>
++<setting+name="Carol">34</setting>
++<setting+name="Ted">56</setting>
++<setting+name="Alice">78</setting>
</settings>|7odk4^0|H|C|1K|D|71|D|21|15|0|3C|2R|1|0|0|D|1A|D|0|0|0|0|0|0^^$0|$1|$2|3|4|5|6|$7|8]]|9|$2|3|4|5|6|$7|A]]]|B|@$C|D|E|F|2|G|H|14|I|@$J|15|K|16|L|M]|$J|17|K|18|L|M]|$J|19|K|1A|L|M]]|N|@$J|1B|K|1C|C|1D]|$J|1E|K|1F|C|1G]]|6|$]]|$C|O|E|P|2|G|H|1H|I|@$J|1I|K|1J|L|M]|$J|1K|K|1L|L|M]]|N|@]|6|$]]|$C|Q|E|R|2|S|H|1M|I|@]|N|@]|6|$T|U]]|$C|V|E|W|2|G|H|1N|I|@]|N|@]|6|$]]|$C|X|E|Y|2|S|H|1O|I|@]|N|@]|6|$T|U]]|$C|Z|E|10|2|G|H|1P|I|@]|N|@]|6|$]]|$C|11|E|12|2|S|H|1Q|I|@]|N|@]|6|$T|U]]|$C|13|E|-4|2|G|H|1R|I|@]|N|@]|6|$]]]]

The following is the utility function I use to search for nodes in a <code>QDomDocument</code> using an XPath expression. It uses the <code>QDomNodeModel</code> class suggested by @Alejandro, downloadable from <a href="https://adared.ch/qdomnodemodel-qxmlquery" rel="nofollow noreferrer">https://adared.ch/qdomnodemodel-qxmlquery</a>. It is based on the usage example from <a href="https://www.qtcentre.org/threads/37645-QAbstractXmlNodeModel-implementation-QDomNodeModel-QXmlQuery" rel="nofollow noreferrer">https://www.qtcentre.org/threads/37645-QAbstractXmlNodeModel-implementation-QDomNodeModel-QXmlQuery</a>. Thanks to Stanislaw Adaszewski, who provided both the <code>QDomNodeModel</code> class and the usage example. 

There are a few methods in <code>QDomNodeModel</code> that are commented as not implemented. However, for the simple XML content that I needed to search, <code>QDomNodeModel</code> is sufficient as-is. 

<pre><code>//
/// @brief Search for nodes in a QDomDocument using an XPath.
/// @note I cannot return a QDomNodeList, because it has no public methods for adding items to it.
/// @param[in] doc The document to search.
/// @param[in] fromNode The node in the document to start searching from.
/// e.g., to search the whole document, use &lt;code&gt;doc.documentElement()&lt;/code&gt;.
/// @param[in] xpath The XPath expression.
/// @return A list of found nodes.
//
QList&lt;QDomNode&gt; findNodes( QDomDocument const &amp; doc, QDomNode const &amp; fromNode, QString const &amp; xpath )
{
 qDebug( "%s", __FUNCTION__ );
 QList&lt;QDomNode&gt; foundNodes;

 //------------------------------
 // The name pool that everybody shares.
 QXmlNamePool pool;

 //------------------------------
 // The model that wraps the document.
 QDomNodeModel model( pool, doc );

 //------------------------------
 // The query.
 // XQuery10 means the default XQuery 1.0 language, as opposed to XSLT20.
 QXmlQuery query( /*QXmlQuery::XQuery10,*/ pool );

 // Operate on the given node.
 QXmlNodeModelIndex fromIndex = model.fromDomNode( fromNode );
 query.setFocus( QXmlItem( fromIndex ) );

 // The query statement.
 query.setQuery( xpath );
 if ( !query.isValid() )
 {
 qDebug( "Query is not valid" );
 return foundNodes;
 }

 //------------------------------
 // The destination for the result of the query.
 QXmlResultItems result;

 //------------------------------
 // Evaluate the query.
 query.evaluateTo( &amp;result );
 if ( result.hasError() )
 {
 qDebug( "Query evaluation failed" );
 return foundNodes;
 }

 //------------------------------
 // The result of the query.
 qDebug( "Query result:" );
 while ( !result.next().isNull() )
 {
 QXmlNodeModelIndex index = result.current().toNodeModelIndex();
 QDomNode node = model.toDomNode( index );
 qDebug( " %d %s: %s", node.nodeType(), qPrintable( node.nodeName() ), qPrintable( node.nodeValue() ) );
 foundNodes &lt;&lt; node;
 }

 return foundNodes;
}
</code></pre>

In my application, I load an XML file, and use the above utility function to search it.

<pre><code>//------------------------------
// The path of the XML file.
QString path = "settings.xml";

//------------------------------
// Open the file.
QFile file( path );
if ( !file.open( QIODevice::ReadOnly ) )
{
 qDebug( "Failed to open '%s': %s", qPrintable( path ), qPrintable( file.errorString() ) );
 return;
}

//------------------------------
// Load the file into a document.
QDomDocument doc;
QString error;
int line;
int column;
if ( !doc.setContent( &amp;file, &amp;error, &amp;line, &amp;column ) )
{
 qDebug( "%s(%d,%d): %s", qPrintable( path ), line, column, qPrintable( error ) );
 return;
}

//------------------------------
// The document root element.
QDomElement rootElem = doc.documentElement();

//------------------------------
// Search for an element whose name attribute has a certain value.
QString name = "Alice";
QString xpath = QString( "setting[@name='%1']" ).arg( name );
QList&lt;QDomNode&gt; foundNodes = findNodes( doc, rootElem, xpath );

//------------------------------
// Did I find it?
if ( foundNodes.size() &gt; 0 )
{
 QDomElement foundElem = foundNodes.at( 0 ).toElement();

 // Do something with that element. 
 ...
} 
</code></pre>

The example XML content to search.

<pre><code>&lt;?xml version='1.0'?&gt;
&lt;settings&gt;
 &lt;setting name="Bob"&gt;12&lt;/setting&gt;
 &lt;setting name="Carol"&gt;34&lt;/setting&gt;
 &lt;setting name="Ted"&gt;56&lt;/setting&gt;
 &lt;setting name="Alice"&gt;78&lt;/setting&gt;
&lt;/settings&gt;
</code></pre>

I am spoiled (rotten, to be sure) by C# and its XML manipulation classes in the <code>System.Xml</code> namespace. I can load an XML file into an <code>XmlDocument</code>. I can search the whole document for nodes that match an XPath expression, using <code>XmlNode.SelectNodes( "an xpath expression" )</code>. The result is an <code>XmlNodeList</code> that contains <code>XmlNode</code> objects that I can iterate over. 

Now I am using C++ Qt (versions 4.7.1 and 4.8, but the particular version may not be important). I can load an XML file into a <code>QDomDocument</code>. But, I am frustrated that I cannot search the document using an XPath expression in a similar way that I did in C#.

I have had limited success using <code>QXmlQuery</code> to find stuff in the XML file. If I write the query in just the right way, I can obtain a <code>QStringList</code> of results, iterate that <code>QStringList</code>, and then store the data somewhere for use later.

But, I still want to be able to obtain a collection of <code>QDomNode</code> objects that are in the document, directly via an XPath expression. One specific use case is to find one element whose "name" attribute has a certain value, and then replace that element with a new element. That is why I want the <code>QDomNode</code> object itself, not just some string-based or other representation of the XML content that <code>QXmlQuery</code> can provide. For the specific use case just mentioned, I am getting by using <code>QDomElement.elementsByTagName()</code> and iterating those elements, but it is not as flexible nor as cool as XPath.

Is it just wishful thinking? Would it be worth the effort to develop some new class that implements the <code>QAbstractXmlReceiver</code> interface? Or, would I just end up with a new collection of data that has no direct relationship to the <code>QDomNode</code> objects in the <code>QDomDocument</code>?

Search for nodes in a QDomDocument using XPath

数据存储

 我被System.Xml名称空间中的C#及其XML操作类宠坏了(当然是坏了)。我可以将XML文件加载到XmlDocument中。我可以使用XmlNode.SelectNodes( "an xpath expression" )在整个文档中搜索与XPath表达式匹配的节点。结果是一个包含我可以遍历的XmlNode对象的...

问使用XPath搜索QDomDocument中的节点
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