From Forum Nokia Wiki

ID		Creation date	June 8, 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 you parse XML with QXmlStreamReader. The QXmlStreamReader class provides a fast parser for reading well-formed XML via a simple streaming API.

This snippet can be self-signed. As it does not use any API which require developer/certified signing.

Preconditions

• Download and Install latest version Qt for Symbian - Installation packages which has links on how to install the latest version

QXmlStreamReader Example

XML file

<?xml version="1.0" encoding="UTF-8" ?>
<persons>
	<person>
		<firstname>John</firstname>
		<surname>Doe</surname>
		<email>john.doe@example.com</email>
		<website>http://en.wikipedia.org/wiki/John_Doe</website>
	</person>
	<person>
		<firstname>Jane</firstname>
		<surname>Doe</surname>
		<email>jane.doe@example.com</email>
		<website>http://en.wikipedia.org/wiki/John_Doe</website>
	</person>
	<person>
		<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);
	}
	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;
	}
	/* 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("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've been able to parse the XML and display it in the UI.

Supplementary material

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

Parsing XML with attributes

Lets take example of parsing following XML file

<?xml version="1.0" encoding="UTF-8" ?>
<persons>
	<person firstname="abc" surname="def" number="1234" />
	<person firstname="ghi" surname="jkl" number="51234" />
	<person firstname="mno" surname="pqr" number="61234" />
	<person firstname="stv" surname="wxy" number="81234" />
	<person firstname="zab" surname="cde" number="61234" />
</persons>

Header file

#include <QtXml/QXmlStreamReader>
 
class ContactDatabse
{
public:
	ContactDatabse(QString firstName, QString surName, QString phoneNumber);
	~ContactDatabse();
	QString getFirstName();
	QString getSurName();
	QString getPhoneNumber();
private:
	QString firstName;
	QString surName;
	QString phoneNumber;
};
 
class QXSRExample : public QMainWindow {
	Q_OBJECT
 
public:
	QXSRExample(QWidget *parent = 0);
	~QXSRExample();
 
private slots:
	void parseXML();
 
private:
	QPointer<QVBoxLayout> _layout;
 
	void setupUI();
	void addPersonsToUI();
	void parsePerson(QXmlStreamReader& reader);
	QList<ContactDatabse> database;
};

Source file

/* The implementaion of parseXML() is same as explained in above example, so ommitted from here */
 
void QXSRExample::parsePerson(QXmlStreamReader& xml)
{
   /* parse each tag and add data to list 
   *We'll continue the loop until we hit an EndElement named persons
   */
	while (!xml.atEnd()) 
	{
	    /* check whether it is starting of tag <person> , if yes then parse it
		*/
		if (xml.isStartElement() && xml.name() == "person") 
		{
		    /* get all attributes and its value of a tag in attrs variable.
			*/
			QXmlStreamAttributes attrs = xml.attributes();
			/*get value of each attribute from QXmlStreamAttributes */
			QStringRef fName = attrs.value("firstname");
			QStringRef sName = attrs.value("surname");
			QStringRef pNumber = attrs.value("number");
 
			  if (fName.isEmpty())
				  {
				  xml.readNext();
				  continue;
				  }
			/*create database of one person*/
			ContactDatabse data(fName.toString(),sName.toString(),pNumber.toString());
			/*add database to list*/
            database.append(data);
		}
		else if(xml.isEndElement() && xml.name() == "persons") 
		{
		   /*if EndElement is persons then stop the loop and create UI */
			addPersonsToUI();
			return;
		}
		xml.readNext();
	}
}
 
void QXSRExample::addPersonsToUI() 
{
    /* add all contact data to UI */
	while(!database.isEmpty()) 
	{
		QGroupBox* personGB = new QGroupBox("Person");
		QFormLayout* layout = new QFormLayout;
		ContactDatabse person = database.takeFirst();
		layout->addRow("First name", new QLineEdit(person.getFirstName()));
		layout->addRow("Surname", new QLineEdit(person.getSurName()));
		layout->addRow("Phone Number", new QLineEdit(person.getPhoneNumber()));
 
		personGB->setLayout(layout);
		this->_layout->addWidget(personGB);
	}
}

Postconditions

You've been able to parse the XML and display it in the UI.

Example Code

• Download Code Example from here

See also

• QXmlStreamReader documentation