QT reading and writing XML files

One 、 brief introduction

Use XML modular , stay .pro Add... To the file QT += xml , And add the corresponding header file
#include
#include perhaps #include .

QtXml Module provides a read and write XML The flow of documents , The parsing method includes DOM and SAX.
（1）DOM（Document ObjectModel）： take XML The file is represented as a tree , Facilitate random access to the nodes , But it consumes relatively more memory .
（2）SAX（Simple APIfor XML）： An event driven XML API, Close to the bottom , Faster , But it is not convenient for random access to any node .

Two 、QDomDocument Read and write files

1、 Read xml file

Read a xml file , adopt QtTree Control is displayed , The effect is as follows ：

testXML.xml The original document

<?xml version="1.0" encoding="UTF-8"?>
<class type="school">
	< name >testXML</ name >
	< Address >
		< Province > Shanxi Province </ Province >
		< City > Taiyuan City </ City >
		< District > Small store area </ District >
	</ Address >
	< School >
		< name > Taiyuan No.1 Middle School </ name >
		< Category > Senior high school </ Category >
	</ School >
	< In grade one >
		< Class one >
			< The number of >24</ The number of >
			< The male to female ratio >1:2</ The male to female ratio >
		</ Class one >
		< Class two >
			< The number of >25</ The number of >
			< The male to female ratio >3:2</ The male to female ratio >
		</ Class two >
		< Class three >
			< The number of >25</ The number of >
			< The male to female ratio >2:3</ The male to female ratio >
		</ Class three >
	</ In grade one >
</class>

1、 Read xml

//  Select File 
void Dialog::on_pushBtn_open_clicked()
{
    
    QString sFileName = QFileDialog::getOpenFileName(this," choice XML file ","/","xml files(*.xml)");

    // Judge whether the file exists 
    QFile fileName(sFileName);
    if(!fileName.exists())
    {
    
        return;
    }

    ReadXMLFile(sFileName);
}

//  Select the file and open 
void Dialog::ReadXMLFile(const QString sFileName)
{
    
    QFile file(sFileName);
    if(file.open(QIODevice::ReadOnly))
    {
    
        QDomDocument dom("TestXML");
        if (dom.setContent(&file))
        {
    
            ui->treeWidget->clear();
            ui->treeWidget->header()->setSectionResizeMode(QHeaderView::ResizeToContents);

            QDomElement docElem = dom.documentElement();
            ShowXMLDoc(docElem, NULL);
            ui->treeWidget->expandAll();
        }
    }

    file.close();
}

//  Read recursively xml Content and display it in the tree control 
void Dialog::ShowXMLDoc(QDomElement &docElem, QTreeWidgetItem *pItem)
{
    
    QDomNode node = docElem.firstChild();
    if(node.toElement().isNull())
    {
    
        pItem->setText (1, docElem.text());
    }

    while(!node.isNull())
    {
    
        QDomElement element = node.toElement(); // try to convert the node to an element.
        if( !element.isNull() )
        {
    
            QTreeWidgetItem *item;
            if( pItem )
            {
    
                pItem->setFlags(Qt::ItemIsUserCheckable|Qt::ItemIsEnabled|Qt:: ItemIsSelectable);
                //pItem->setCheckState(0, Qt::Unchecked);
                item = new QTreeWidgetItem(pItem);
            }
            else
            {
    
                item = new QTreeWidgetItem(ui->treeWidget);
            }

            item->setFlags(Qt::ItemIsUserCheckable|Qt::ItemIsEnabled|Qt:: ItemIsSelectable);
            //item->setCheckState(0, Qt::Unchecked);

            item->setText(0, element.tagName());

            ShowXMLDoc(element, item);

            if( pItem )
            {
    
                pItem->addChild(item);
            }
            else
            {
    
                ui->treeWidget->addTopLevelItem(item);
            }
        }

        node = node.nextSibling();
    }

    return;
}

2、 Write generation xml

Generate xml file , The effect is as follows ：

The code is as follows ：

int DomDocument::writeXml()
{
    
    QString fileName = "testXML.xml";
    QFile file(fileName);
    if (!file.open(QIODevice::WriteOnly | QIODevice::Truncate))
    {
    
        return -2;
    }

    QTextStream out(&file);
    QDomDocument doc;
    QDomText text;
    QDomElement element;
    QDomAttr attr;
    QDomProcessingInstruction instruction;
    instruction = doc.createProcessingInstruction( "xml", "version = \'1.0\' encoding=\'UTF-8\'" );
    doc.appendChild( instruction );

    QDomElement root = doc.createElement( "class" );
    attr = doc.createAttribute( "type" );
    attr.setValue("school");
    root.setAttributeNode(attr);
    doc.appendChild(root);

    element = doc.createElement( " name " );
    text = doc.createTextNode( "testXML" );
    element.appendChild(text);
    root.appendChild(element);


    element = doc.createElement( " Address " );

    QDomElement childElement = doc.createElement( " Province " );
    text = doc.createTextNode( " Shanxi Province " );
    childElement.appendChild(text);
    element.appendChild(childElement);

    childElement = doc.createElement( " City " );
    text = doc.createTextNode( " Taiyuan City " );
    childElement.appendChild(text);
    element.appendChild(childElement);

    root.appendChild(element);

    doc.save(out, 4);       //each line space of file is 4
    return 0;
}