the program closes without error

[serkan_tr]

I am trying to communicate c++ with qml, but the program closes. the program is being built without any problems, but when I run it, it opens and closes.

#ifndef COMM_H
#define COMM_H

#include <QObject>
#include <QDebug>
#include <QTimer>
#include <string>
using namespace std;

class SerialPort: public QObject{
    Q_OBJECT
private:
    QTimer* timer;
    int i;
public:
    SerialPort();
    ~SerialPort();

};

class CommQMl: public QObject{
    Q_OBJECT
    Q_PROPERTY(string name READ name WRITE setName NOTIFY nameChanged)
    Q_PROPERTY(int number_class READ number_class WRITE setNumber_class NOTIFY number_classChanged)
private:

    string m_name;

    int m_number_class;

public:
    CommQMl();
    ~CommQMl();
    string name() const;
    void setName(const string &newName);
    int number_class() const;
    void setnumber_class(int newNumber_class);

signals:
    void nameChanged();
    void number_classChanged();
};



#endif // COMM_H

#include "comm.h"



SerialPort::SerialPort():i(0){
    qDebug() << "SerialPort class destroyed";
}
SerialPort::~SerialPort(){
    qDebug() << "SerialPort class created";
    delete timer;
}

///////////////////////////////////////////////////////
CommQMl::CommQMl(): m_number_class(0)
{
    qDebug() << "CommQML class created";
}

CommQMl::~CommQMl()
{
    qDebug() << "CommQML class destroyed";
}
string CommQMl::name() const
{
    return m_name;
}
void CommQMl::setName(const string &newName)
{
    if (m_name == newName)
        return;
    m_name = newName;
    emit nameChanged();
}


int CommQMl::number_class() const
{
    return m_number_class;
}

void CommQMl::setnumber_class(int newNumber_class)
{
    if (m_number_class == newNumber_class)
        return;
    m_number_class = newNumber_class;
    emit number_classChanged();
}

main.cpp

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


int main(int argc, char *argv[])
{
    qmlRegisterType<CommQMl>("qmlcomm", 1, 0, "CommQMl");
    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;
    const QUrl url(QStringLiteral("qrc:/main.qml"));
    QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
                     &app, [url](QObject *obj, const QUrl &objUrl) {
        if (!obj && url == objUrl)
            QCoreApplication::exit(-1);
    }, Qt::QueuedConnection);

    QTimer timer;
    engine.load(url);
    int i = 0;
    QObject* rootObject = engine.rootObjects().first();
    CommQMl* myObject = rootObject->findChild<CommQMl*>("cpp_comm");

    QObject::connect(&timer, &QTimer::timeout, [&]() {
             myObject->setnumber_class(10);
        });

    timer.start(1000);
    app.exec();

    return 0 ;
}

main.qml

import QtQuick 2.15
import QtQuick.Window 2.15
import qmlcomm 1.0
Window {
    width: 640
    height: 480
    visible: true
    title: qsTr("Hello World")

    CommQMl{
        id:cpp_comm
    }


    Rectangle{
        height: 100
        width:  100
        anchors.centerIn: parent
        color:"black"
        Text {
            id: aaa
            text: cpp_comm.number_class
            anchors.centerIn: parent
            color:"green"
        }
    }
}

[Christian Ehrlicher]

@serkan_tr said in the program closes without error:

CommQMl* myObject = rootObject->findChild<CommQMl*>("cpp_comm");

You should check if this returns a valid pointer.

[serkan_tr]

@serkan_tr I noticed that the problem is that the myObject object is not found by the program, but I don't understand why it can't find it

[serkan_tr]

@Christian-Ehrlicher

  QObject* rootObject = engine.rootObjects().first();
    CommQMl* myObject = rootObject->findChild<CommQMl*>("cpp_comm");
    if(myObject){
        qDebug("found");
    }

in this code if() command returns 0

CommQMl* myObject = rootObject->findChild<CommQMl*>("cpp_comm");
    qDebug() << myObject;

output: QObject(0x0)

[Christian Ehrlicher]

So you should make sure you get the correct instance instead a nullptr I would guess.

[J.Hilk]

@serkan_tr replace

id: cpp_com

with

objectName: "cpp_com"

and you might actually be able to find the child by object name :P

also properly initialise your base QObject.

[serkan_tr]

@J-Hilk
yes that worked, thank you