Integrating c++ and qml

Question

Okay I'm resetting this whole post because I guess I didn't have enough " Minimal, Complete, and Verifiable example " which really is the entirety of my question, because I am just so LOST on slots and signals.. so here's 2nd attempt, I will leave out flower.cpp, but know it has a function in there

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQuickView>
#include <QtQuick>
#include <QNetworkAccessManager>
#include <iostream>
#include <QJsonObject>
#include <QJsonArray>
#include <QJsonDocument>
#include <QNetworkReply>
#include <QObject>
#include "flower.h"



void Flower::onClicked(){
//code i've been trying to test all day
}

flower.h (my header for the class flower (the function))

#ifndef FLOWER_H
#define FLOWER_H

#include <QObject>

class Flower
{
private slots:
void onClicked();

};
#endif // FLOWER_H

main.cpp (this is where my app QML is started from, and I'm trying to setup the connection of signal and slot there)

QQuickView home;
home.setSource(QUrl::fromLocalFile("main.qml"));
home.show();
QObject *homePa = home.rootObject();
QObject *buttF = homePa->findChild<QObject*>("buttFObject");
QObject::connect(buttF, SIGNAL(qmlClick()), buttF,
                 SLOT(Flower.onClicked()));

this is the navmenu with the mousearea that I want to have the onClicked: command attached

Rectangle {
    signal qmlClick();

    id: navMenu
    color: "#00000000"
    radius: 0
    anchors.fill: parent
    z: 3
    visible: false
    border.width: 0
    transformOrigin: Item.Center
               MouseArea {
                id: buttFArea
                objectName: buttFObject
                anchors.fill: parent
                onClicked: navMenu.qmlClick()
            }
           }

When I try to run right now I receive this error "W libAHDP.so: QObject::connect: Cannot connect (null)::qmlClick() to (null)::Flower.onClicked()"

Apologies for my first post being very misleading and mixed up I hope this is more clear on what my issue is

Please provide a minimal reproducible example - right now your question has far too much code in it that isn't relevant to the actual problem, making it much harder for anyone to help. — BoBTFish

eyllanesc eyllanesc · Accepted Answer · 2019-03-15T07:20:55

Only QObjects can have slots so Flower must inherit from QObject. On the other hand you are using an approach that always brings problems that is to try to obtain a QML element from C++, instead you must export the C++ element to QML using setContextProperty():

flower.h

#ifndef FLOWER_H
#define FLOWER_H

#include <QObject>

class Flower : public QObject
{
    Q_OBJECT
public:
    explicit Flower(QObject *parent = nullptr);
    Q_SLOT void onClicked();
};

#endif // FLOWER_H

flower.cpp

#include "flower.h"
#include <QDebug>

Flower::Flower(QObject *parent) : QObject(parent)
{}
void Flower::onClicked()
{
    qDebug()<< __PRETTY_FUNCTION__;
}

main.cpp

#include <QGuiApplication>
#include <QQuickView>
#include <QQmlContext>
#include "flower.h"

int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
    QGuiApplication app(argc, argv);
    Flower flower;
    QQuickView view;
    view.rootContext()->setContextProperty("flower", &flower);
    view.setSource(QUrl(QStringLiteral("qrc:/main.qml")));
    view.show();
    return app.exec();
}

main.qml

import QtQuick 2.9

Rectangle {
    color: "#00000000"
    anchors.fill: parent
    transformOrigin: Item.Center
    MouseArea {
        id: buttFArea
        anchors.fill: parent
        onClicked: flower.onClicked()
    }
}

For more information I recommend reading Best Practices for QML and Qt Quick

Integrating c++ and qml

1 Answers