#ifndef STRINGHELPER_H
#define STRINGHELPER_H
 
#include <QObject>
#include <QString>
 
class StringHelper : public QObject
{
    Q_OBJECT
public:
    StringHelper(QObject *parent = 0) : QObject(parent), reverse(false) { }
 
    Q_INVOKABLE QString echo(const QString &text) const {
        if(reverse == false) { return text; }
 
        QString reversed;
        for(QString::const_iterator it = text.begin(); it != text.end(); it++) {
            reversed.push_front(*it);
        }
 
        return reversed;
    }
 
public slots:
    void toggleEcho(bool reverse) { this->reverse = reverse; }
 
protected:
    bool reverse;
};
 
#endif // STRINGHELPER_H

import Qt 4.7
 
Rectangle {
    id: rect
 
    property string text: "Using Qt class to echo this"
 
    function updateUI() {
        StringHelper.toggleEcho(button.pressed); // calling StringHelper::toggleEcho
        text.text = StringHelper.echo(rect.text) // calling StringHelper::echo
    }
 
    anchors.fill: parent
    color: "black"
 
    Component.onCompleted: updateUI()
 
    Text {
        id: text
        anchors.centerIn: parent
        color: "white"
    }
 
    Rectangle {
        id: button
 
        property bool pressed: false
 
        width: 100; height: 40
        anchors.right: parent.right; anchors.rightMargin: 20
        anchors.bottom: parent.bottom; anchors.bottomMargin: 20
        radius: 6
        color: pressed ? "gray" : "white"
 
        Text {
            anchors.centerIn: parent
            text: "Reverse"
        }
 
        MouseArea {
            anchors.fill: parent
            onClicked: { button.pressed = !button.pressed; updateUI() }
        }
    }
}

#include <QApplication>
#include <QDeclarativeView>
#include <QDeclarativeContext>
#include "stringhelper.h"
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
 
    StringHelper stringHelper;
 
    QDeclarativeView view;
    view.setResizeMode(QDeclarativeView::SizeRootObjectToView);
    view.rootContext()->setContextProperty("StringHelper", &stringHelper);
    view.setSource(QUrl("./ui.qml"));
 
#if defined(Q_WS_S60) || defined(Q_WS_MAEMO)
    view.showMaximized();
#else
    view.setGeometry(100, 100, 800, 480);
    view.show();
#endif
 
    return a.exec();
}