QML object implemented in C++ does not call the destructor

[dmendizabal]

I have a QML object (CppObject) implemented in C++ which is then registered with qmlRegisterType.
It is instantiated in QML document without any problem, but when the application is closed (Qt.quit()), the C++ destructor of CppObject class is not called.

I'm using Qt 5.7 and Quick Controls 2.

Any idea, how to fix his problem?

[jpnurmi]

Hard to say without seeing any code. :) Are you using QQmlApplicationEngine to load the QML code? Is it allocated on the stack in main()?

[dheerendra]

It works and we are using it. Do you have destructor ? See the sample here.

QML

MyLog{
    id : log
}
MouseArea {
    anchors.fill: parent
    onClicked: {
        console.log("I am quitting")
        log.destroy()// Without calling this destroy also it works.
        Qt.quit();
    }
}

C++
Logging::Logging()
{
qDebug() << Q_FUNC_INFO << " Constructor " <<endl;
}

void Logging::callme(){
qDebug() << Q_FUNC_INFO << " Called me " <<endl;
}

Logging::~Logging(){
qDebug() << Q_FUNC_INFO << " Destructor " <<endl;
}

main.cpp
qmlRegisterType<Logging>("Log",1,0,"MyLog");

[dmendizabal]

I have a test case similar as your implementation and the destructor is called only when I use destroy() as your example.
The moment I don't call destroy(), the destructor is not called.

[A Former User]

@dmendizabal Hi! Please provide a complete minimal example so that we can try to reproduce the behaviour.

[dmendizabal]

@Wieland Please find example below:

main.cpp

#include <QtQuick>
#include "message.h"

int main (int argc, char *argv[])
{
  QGuiApplication app(argc, argv);
  qmlRegisterType<CMessage>("com.message", 1, 0, "Message");

  QQmlApplicationEngine engine;
  engine.load(QUrl(QLatin1String("qrc:/main.qml")));

  return app.exec();
}

message.h ---> QML object implemented in C++

#include <QObject>

class CMessage : public QObject
{
  Q_OBJECT
public:
  explicit CMessage(QObject *parent = 0);
  ~CMessage();
};

message.cpp ---> QML object implementation in C++

#include <QtGui>
#include "message.h"

CMessage::CMessage(QObject *parent) : QObject(parent)
{
 qDebug()<<"Constructor";
}

CMessage::~CMessage()
{
  qDebug()<<"Destructor";
}

main.qml ---> QML main window

import QtQuick 2.7
import QtQuick.Controls 2.0
import QtQuick.Layouts 1.3

ApplicationWindow {
    visible: true
    width: 640
    height: 480

    StackView {
        id: id_stack
        anchors.fill: parent
        initialItem: "qrc:page1.qml"
    }
}

page1.qml ---> QML page

import QtQuick 2.5
import QtQuick.Controls 2.0
import QtQuick.Layouts 1.3
import QtQuick.Window 2.0
import com.message 1.0

Page {
    id: id_item

    header: ToolBar {
        id: id_toolbar
        RowLayout {
            id: id_layout
            ToolButton {
                id: id_quitButton
                text: qsTr("Quit")
                onClicked: Qt.quit()
            }
        }
    }

    Message {
        id: id_message
    }
}

[jpnurmi]

@dmendizabal Thank you for the test case. This is StackView's fault for not claiming proper ownership of a dynamically instantiated initial item. The leak has been fixed in Qt 5.7.1.

[dmendizabal]

@jpnurmi Thanks.
I will wait for 5.7.1 and it may resolve also another problem I'm facing that looks to be in relation to StackView.

[jpnurmi]

@dmendizabal What is the other problem?