How to Expose a Qt C++ Class to QML

isan

In QT I use this method to define a class in another class

.h:

#ifndef RealTime_H
#define RealTime_H

#include <QDialog>
#include "randomwalk.h"


class RealTime : public QDialog {
    Q_OBJECT
public:
    RealTime(QWidget *parent = 0);
    ~RealTime();

     // RandomWalk is a thread class
     RandomWalk *dataSource;

static void OnData(void *self, double elapsedTime);

#endif

.cpp:

RealTime::RealTime(QWidget *parent) :
    QDialog(parent)
{
 // Start the random data generator
    dataSource = new RandomWalk(OnData, this);
    dataSource->start();
}

Now in QML I register c++ class and set id in .qml file

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QtQml>
#include <realtime.h>
#include <randomwalk.h>

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


    qmlRegisterType <RealTime>("realt",1,0,"RealTime");
    qmlRegisterType<RandomWalk> ("thread",1,0,"RandomWalk");


    QQmlApplicationEngine engine;

    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
    if (engine.rootObjects().isEmpty())
        return -1;

    return app.exec();
}

.qml:

import QtQuick 2.11
import QtQuick.Controls 2.4
import realt 1.0
import thread 1.0
Page {
    id: page
    width: screen.width
    height: screen.height
    property alias button1: button1

    RealTime{
        id:mRealtime
    }
    
    RandomWalk{
        id:mThread
    }
  Button {
        id: button
        x: -74
        y: -110
        text: qsTr("Config 2")
        anchors.verticalCenterOffset: -6
        anchors.horizontalCenterOffset: -24
        anchors.horizontalCenter: parent.horizontalCenter
        anchors.verticalCenter: parent.verticalCenter
       // onClicked: 
    }

How should I define
dataSource = new RandomWalk(OnData, this);in qml ?

isdsi

This may help you.
https://doc.qt.io/qt-5/qtqml-javascript-dynamicobjectcreation.html

isan

I know it creates when we define an object,
RandomWalk{
id:mThread
}
But how do I define an onData input?

GrecKo

What's an onData input? What do you want to do with it?

Have you read this page https://doc.qt.io/qt-5/qtqml-cppintegration-overview.html ?
I'm not sure what you need but it might be a property, a signal or a slot.

johngod

In your RealTime class you need to expose the RandomWalk property to qml, using setters and getters and the macro Q_PROPERTY.
Something like this:

class RealTime : public QDialog {
    Q_OBJECT
	Q_PROPERTY(RandomWalk walk READ randomWalk WRITE setRandomWalk /*NOTIFY randomWalkChanged*/)
// in line above walk is the property name that gets exposed to qml
	
	RandomWalk randomWalk() { return *randomWalk;}
public slots: 
	void setRandomWalk(RandomWalk randomWalk_){ dataSource = new RandomWalk(randomWalk_);} 
	.......
	RandomWalk *dataSource;
       .........

Then in qml you can do:

RandomWalk{
    id: mThread
}
	
RealTime{
    id: mRealtime
	walk: mThread
}

Note that I havent tested the code above, so you may need to do some tunning, but hopefully you get the ideia :)