CS001436 - Using QXmlStreamReader to parse XML

From Forum Nokia Wiki

ID	CS001436	Creation date	June 18, 2009
Platform	Qt	Tested on devices	5800 XpressMusic
Category	Qt for Symbian	Subcategory

Keywords (APIs, classes, methods, functions): Qt, XML, SAX, QXmlStreamReader

Overview

This example shows you how to parse well-formed XML with QXmlStreamReader. Qt documentation states that it is a faster and more convenient replacement for Qt's own SAX parser (QXmlSimpleReader) and it's also faster, as well as in some cases more convenient, than a DOM tree (QDomDocument).

Preconditions

Install latest Qt for S60 see Qt for S60 - Installation packages
Check this link for installation guide: How to install the package.
Go through this article: Getting started with Qt for S60

QXmlStreamReader Example

XML file

<?xml version="1.0" encoding="UTF-8" ?>
<persons>
    <person id="1">
        <firstname>John</firstname>
        <surname>Doe</surname>
        <email>john.doe@example.com</email>
        <website>http://en.wikipedia.org/wiki/John_Doe</website>
    </person>
    <person id="2">
        <firstname>Jane</firstname>
        <surname>Doe</surname>
        <email>jane.doe@example.com</email>
        <website>http://en.wikipedia.org/wiki/John_Doe</website>
    </person>
    <person id="3">
        <firstname>Matti</firstname>
        <surname>Meikäläinen</surname>
        <email>matti.meikalainen@example.com</email>
        <website>http://fi.wikipedia.org/wiki/Matti_Meikäläinen</website>
    </person>
</persons>

Header file

#include <QtXml/QXmlStreamReader>
 
class QXSRExample : public QMainWindow {
    Q_OBJECT
 
public:
    QXSRExample(QWidget *parent = 0);
    ~QXSRExample();
 
private slots:
    void parseXML();
 
private:
    QPointer<QVBoxLayout> _layout;
 
    void setupUI();
 
    QMap<QString, QString> parsePerson(QXmlStreamReader& xml);
    void addElementDataToMap(QXmlStreamReader& xml,
                             QMap<QString, QString>& map) const;
 
    void addPersonsToUI(QList< QMap<QString,QString> >& persons);
};

Source file

void QXSRExample::parseXML() {
    /* We'll parse the example.xml */
    QFile* file = new QFile(":/example.xml");
    /* If we can't open it, let's show an error message. */
    if (!file->open(QIODevice::ReadOnly | QIODevice::Text)) {
        QMessageBox::critical(this,
                              "QXSRExample::parseXML",
                              "Couldn't open example.xml",
                              QMessageBox::Ok);
        return;
    }
    /* QXmlStreamReader takes any QIODevice. */
    QXmlStreamReader xml(file);
    QList< QMap<QString,QString> > persons;
    /* We'll parse the XML until we reach end of it.*/
    while(!xml.atEnd() &&
            !xml.hasError()) {
        /* Read next element.*/
        QXmlStreamReader::TokenType token = xml.readNext();
        /* If token is just StartDocument, we'll go to next.*/
        if(token == QXmlStreamReader::StartDocument) {
            continue;
        }
        /* If token is StartElement, we'll see if we can read it.*/
        if(token == QXmlStreamReader::StartElement) {
            /* If it's named persons, we'll go to the next.*/
            if(xml.name() == "persons") {
                continue;
            }
            /* If it's named person, we'll dig the information from there.*/
            if(xml.name() == "person") {
                persons.append(this->parsePerson(xml));
            }
        }
    }
    /* Error handling. */
    if(xml.hasError()) {
        QMessageBox::critical(this,
                              "QXSRExample::parseXML",
                              xml.errorString(),
                              QMessageBox::Ok);
    }
    /* Removes any device() or data from the reader
     * and resets its internal state to the initial state. */
    xml.clear();
    this->addPersonsToUI(persons);
}
 
QMap<QString, QString> QXSRExample::parsePerson(QXmlStreamReader& xml) {
    QMap<QString, QString> person;
    /* Let's check that we're really getting a person. */
    if(xml.tokenType() != QXmlStreamReader::StartElement &&
            xml.name() == "person") {
        return person;
    }
    /* Let's get the attributes for person */
    QXmlStreamAttributes attributes = xml.attributes();
    /* Let's check that person has id attribute. */
    if(attributes.hasAttribute("id")) {
        /* We'll add it to the map. */
        person["id"] = attributes.value("id").toString();
    }
    /* Next element... */
    xml.readNext();
    /*
     * We're going to loop over the things because the order might change.
     * We'll continue the loop until we hit an EndElement named person.
     */
    while(!(xml.tokenType() == QXmlStreamReader::EndElement &&
            xml.name() == "person")) {
        if(xml.tokenType() == QXmlStreamReader::StartElement) {
            /* We've found first name. */
            if(xml.name() == "firstname") {
                this->addElementDataToMap(xml, person);
            }
            /* We've found surname. */
            if(xml.name() == "surname") {
                this->addElementDataToMap(xml, person);
            }
            /* We've found email. */
            if(xml.name() == "email") {
                this->addElementDataToMap(xml, person);
            }
            /* We've found website. */
            if(xml.name() == "website") {
                this->addElementDataToMap(xml, person);
            }
        }
        /* ...and next... */
        xml.readNext();
    }
    return person;
}
 
void QXSRExample::addElementDataToMap(QXmlStreamReader& xml,
                                      QMap<QString, QString>& map) const {
    /* We need a start element, like <foo> */
    if(xml.tokenType() != QXmlStreamReader::StartElement) {
        return;
    }
    /* Let's read the name... */
    QString elementName = xml.name().toString();
    /* ...go to the next. */
    xml.readNext();
    /*
     * This elements needs to contain Characters so we know it's
     * actually data, if it's not we'll leave.
     */
    if(xml.tokenType() != QXmlStreamReader::Characters) {
        return;
    }
    /* Now we can add it to the map.*/
    map.insert(elementName, xml.text().toString());
}
 
void QXSRExample::addPersonsToUI(QList< QMap<QString,QString> >& persons) {
    while(!persons.isEmpty()) {
        QGroupBox* personGB = new QGroupBox("Person");
        QFormLayout* layout = new QFormLayout;
        QMap<QString,QString> person = persons.takeFirst();
        layout->addRow("ID", new QLineEdit(person["id"]));
        layout->addRow("First name", new QLineEdit(person["firstname"]));
        layout->addRow("Surname", new QLineEdit(person["surname"]));
        layout->addRow("E-mail", new QLineEdit(person["email"]));
        layout->addRow("Website", new QLineEdit(person["website"]));
        personGB->setLayout(layout);
        this->_layout->addWidget(personGB);
    }
}

Postconditions

You are able to parse the XML and display it in the UI.

Supplementary material

You can test QXSRExample with a test application. The application is available for download at Media:QXSRExample.zip.

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