QML and C++ bindings

main.cpp

#include <QApplication>
#include <QQmlApplicationEngine>
#include <QtQml>
#include "worker.h"

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    qmlRegisterType<Worker>("Worker.interface", 1, 0, "Worker");

    QQmlApplicationEngine engine;
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));

    return app.exec();
}

main.qml

import QtQuick 2.3
import QtQuick.Controls 1.2
import Worker.interface 1.0


ApplicationWindow {
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")

    Worker {
        id: worker
    }

    menuBar: MenuBar {
        Menu {
            title: qsTr("File")
            MenuItem {
                text: qsTr("&Open")
                onTriggered: console.log("Open action triggered");
            }
            MenuItem {
                text: qsTr("Exit")
                onTriggered: Qt.quit();
            }
        }
    }

    TextInput {
        id: pWidth
        x: 210
        y: 118
        width: 230
        height: 43
        text: qsTr("width")
        font.pixelSize: 21
        onEditingFinished: worker.calcHeight()
    }

    TextInput {
        id: pHeight
        x: 210
        y: 193
        width: 230
        height: 47
        text: qsTr("height")
        font.pixelSize: 21
    }
}

Worker.cpp

#include "worker.h"

Worker::Worker(QObject *parent) : QObject(parent)
{

}

float Worker::pixelWidth() {
    return _pixelWidth;
}

void Worker::setPixelWidth(float value) {
    _pixelWidth = value;
    emit pixelWidthChanged();
}

float Worker::pixelHeight() {
    return _pixelHeight;
}

void Worker::setPixelHeight(float value) {
    _pixelHeight = value;
    emit pixelHeightChanged();
}

void Worker::calcHeight() {
    _pixelHeight = (_pixelWidth * 9) / 16;
    emit pixelHeightChanged();
}

Worker.h

#ifndef WORKER_H
#define WORKER_H

#include <QObject>

class Worker : public QObject
{
    Q_OBJECT

    Q_PROPERTY(float pixelWidth READ pixelWidth WRITE setPixelWidth NOTIFY pixelWidthChanged)
    Q_PROPERTY(float pixelHeight READ pixelHeight WRITE setPixelHeight NOTIFY pixelHeightChanged)
public:
    explicit Worker(QObject *parent = 0);

    float pixelWidth();
    void setPixelWidth(float value);

    float pixelHeight();
    void setPixelHeight(float value);

    Q_INVOKABLE void calcHeight();

signals:
    void pixelWidthChanged();
    void pixelHeightChanged();

public slots:

private:
    float _pixelHeight;
    float _pixelWidth;
};

#endif // WORKER_H