Quitting, assert runtime error - child, parent

[olivierguzziIDEOL]

Dear all,

I'm working on a desktop client monitoring a wind turbine.
I am programming components in c++ that creates QQmlComponent from a .qml file and then creates a QObject and link it with my window's content Rectangle.

When i call Qt.quit() from the QML, i have a runtime error and don't really know from where it is coming.
I thought i was from the parent - child link but nothing resolved it.

What do you think of that ?
Is there somebody having the same issue ? (I found nothing or nothing helping on google so i think i made something wrong that is evident to Qt programmers).

Error :

ASSERT: "childItems.contains(child)" in file items\qquickitem.cpp, line 2953
Invalid parameter passed to C runtime function.
Invalid parameter passed to C runtime function.
ASSERT: "!m_thread.isRunning()" in file qqmldebugserver.cpp, line 655
Invalid parameter passed to C runtime function.
Invalid parameter passed to C runtime function.

Some time this error is replaced by the CoreIndex >= 0 assert

LogInForm.h

#ifndef LOGINFORM_H
# define LOGINFORM_H

# include <QObject>
# include <QQmlComponent>
# include <QQmlEngine>
# include <QUrl>
# include <QQuickItem>
# include <QtQuick>
# include <QQuickItem>
# include <iostream>

class LogInForm : public QObject
{
    Q_OBJECT
public:

    // Constructor
    explicit LogInForm(QObject *parent = 0, QQmlEngine *engine = 0);

signals:

public slots:

protected slots:
    void onViewStatusChanged(QQmlComponent::Status status);
    void onSubmitForm();

protected:
    QString         _qmlSrcUrl;
    QQmlEngine      *_engine;
    QQmlComponent   *_component;
    QObject         *_qmlComponent;
};

#endif // LOGINFORM_H

LogInForm.cpp

#include "cpp/headers/qtViews/loginform.h"

LogInForm::LogInForm(QObject *parent, QQmlEngine *engine) : QObject(parent)
{
    // Set the QML Source File Path/Url
    _qmlSrcUrl = "qrc:/qml/logInForm.qml";

    // Get the QQmlEngine
    if (engine != 0){
        _engine = engine;
    } else {
        _engine = new QQmlEngine();
    }

    // Create a QQmlComponent Object from QML Source File
    _component = new QQmlComponent(_engine, QUrl(_qmlSrcUrl));

    std::cout << _component->status() << std::endl;
    QList<QQmlError> errors = _component->errors();
    foreach (QQmlError e, errors) {
        std::cout << "(" << e.line() << ", " << e.column() << ") :: " << qPrintable(e.description()) << std::endl << qPrintable(e.toString()) << std::endl;
    }
    // Track when the component is ready
    if(_component->status() == QQmlComponent::Ready)
    {
        onViewStatusChanged(QQmlComponent::Ready);
    } else {
        connect(_component, SIGNAL(statusChanged(QQmlComponent::Status)),
           this, SLOT(onViewStatusChanged(QQmlComponent::Status)));
    }
}

void LogInForm::onViewStatusChanged(QQmlComponent::Status status)
{
    QQuickItem *i = Q_NULLPTR;
    if(status == QQmlComponent::Ready)
    {
        // Create a Qml Object from the created _component
        _qmlComponent = _component->create();

        i = qobject_cast<QQuickItem*>(_qmlComponent);

        // Set Cpp ownership to avoid javascript garbage collector to delete the object
        QQmlEngine::setObjectOwnership(i, QQmlEngine::CppOwnership);

        // Set parent and visual parent
        i->setParentItem(qobject_cast<QQuickItem*>(this->parent()));
        //i->setVisible(true);
        connect( _qmlComponent, SIGNAL(submitForm()), this, SLOT(onSubmitForm()));
    }
}


void LogInForm::onSubmitForm() {
    QString username = _qmlComponent->property("username").toString();
    QString password = _qmlComponent->property("password").toString();
    QString serverAddress = _qmlComponent->property("serverAddress").toString();
    QString serverName = _qmlComponent->property("serverName").toString();

}

Main.cpp

#include <QApplication>
#include <QQmlApplicationEngine>
#include "cpp/headers/qtViews/loginform.h"
#include <iostream>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

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

    QObject *mainWindow = engine.rootObjects().first();
    if (!mainWindow){
        std::cerr << "Main :: mainWindow not found !" << std::endl;
        return EXIT_FAILURE;
    }

    QObject *contentRectangle = mainWindow->findChild<QObject*>("contentRectangle");
    if (!contentRectangle){
        std::cerr << "Main :: contentRectangle not found !" << std::endl;
        return EXIT_FAILURE;
    }
    QObject *logInForm = new LogInForm(contentRectangle, &engine);

    return app.exec();
}

Thank you a lot for helping,
Olivier :)

[sierdzio]

To avoid errors in future, I strongly recommend setting all pointers to nullptr in your header or contructor initializer list. It's not a problem here, but it can quickly become one as the code evolves. Or use smart pointers.

This is unusual way of creating QML interfaces, but looks very cool! :-)

Regarding the errors - I have to say up front that I don't know the answer. I have only a few suspicions, but nothing certain:

• object ownership: QObjects delete their children when they are deleted. _qmlComponent's visual parent is contentRectangle, but it's QObject parent seems to be the _component. Not sure if that is entirely correct
• check if all the objects live in the same thread (with QObject::thread() or was it threadId()?) - maybe that will point you towards the problem
• are you 100% sure that contentRectangle is a QQuickItem? You don't verify if the cast works in LogInForm::onViewStatusChanged
• childItems.contains(child) LogInForm is a child of contentRectangle, and so is the _qmlComponent, but only only one of these is a QQuickItem. Maybe the parent object has a problem with that?
• try running it via thread sanitizer and address sanitizer, maybe they will show mor eprecisely what fails

[dheerendra]

main.qml - What is the top level item ? Is it window or Item ?
loginform.qml - What is top level item ? Is it window or Item ?

This is typical issue of object deleted already is getting delete due to parent child relation ship ?