MVVM example with QT QML + C++

[AROH]

Hello,

I am trying a sample example in MVVM pattern using QT QML + C++, i have drafted the whole example based on the things i read from internet.
But i am unable to execute the same, any help in here will be highly appreciated.

MainModel.h

#ifndef MAINMODEL_H
#define MAINMODEL_H

#include <QObject>

class MainModel
{
private:
    QString _labelTextString;
public:
    virtual ~MainModel() {}

    QString getLabelTextString() const {return _labelTextString;}

    void setLabelTextString(QString &value){
        _labelTextString = value;
    }
};

#endif // MAINMODEL_H

MainViewModel.h

#ifndef MAINVIEWMODEL_H
#define MAINVIEWMODEL_H

#include "mainmodel.h"

class MainViewModel : public QObject
{
    Q_OBJECT

private:
    //mainModel

    MainModel _mainModel;

    Q_PROPERTY(QString labelText READ labelText WRITE setLabelText NOTIFY labelTextChanged)
    QString m_labelText = "Happy";

public:
    explicit MainViewModel(const MainModel& mainModel);

    virtual ~MainViewModel(){}

    Q_INVOKABLE void changeText(QString value)
    {
        setLabelText(value);
    }

    QString labelText() const;

public slots:
void setLabelText(QString labelText);
signals:
void labelTextChanged(QString labelText);
};

#endif // MAINVIEWMODEL_H

MainViewModel.cpp

#include "mainviewmodel.h"

MainViewModel::MainViewModel(const MainModel& mainModel)
{
    _mainModel = mainModel;
}

QString MainViewModel::labelText() const
{
    return m_labelText;
}

void MainViewModel::setLabelText(QString labelText)
{
    if (m_labelText == labelText)
        return;

    m_labelText = labelText;
    _mainModel.setLabelTextString(m_labelText);
    emit labelTextChanged(m_labelText);
}

main.qml

import QtQuick 2.9
import QtQuick.Window 2.2
import QtQuick.Controls 2.2

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

    Label{
            id: sourceTbx
            x: 201
            y: 176
            width: 348
            height: 27;
            anchors.verticalCenterOffset: -50
            anchors.horizontalCenterOffset: 75
            anchors.horizontalCenter: parent.horizontalCenter
            anchors.verticalCenter: parent.verticalCenter
            text: model.labelText
            Binding { target: model; property: "labelText"; value: sourceTbx.text }
    }

    Button {
        x: 244
        y: 361
        width: 113
        height: 37
        anchors.verticalCenterOffset: 140
        anchors.horizontalCenterOffset: 0
        anchors.horizontalCenter: parent.horizontalCenter
        anchors.verticalCenter: parent.verticalCenter
        onClicked: model.changeText("Hai")
    }
}

main.cpp

#include <QGuiApplication>
#include <QQmlContext>
#include <QQmlApplicationEngine>
#include "mainviewmodel.h"

int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);

    QGuiApplication app(argc, argv);

    MainModel mainModell;

    QQmlApplicationEngine engine;
    engine.rootContext()->setContextProperty("model", &mainModell); //i am getting error at this place, if i am commenting this then i can see the Window.
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
    if (engine.rootObjects().isEmpty())
        return -1;

    return app.exec();
}

Thanks in advance !!

Regard's,
Rohith.G

[dheerendra]

MainModel cannot be exposed using to QML.
Do the following in main.

MainModel mainMod;
MainViewModel mainModell(mainMod);

[AROH]

@dheerendra

Thanks for the input, it worked for me.