Issue creating c++ object in qml and passing it to c++ function

[rigu10]

Hello, this is my situation: i have a c++ class that i register as qml type and instantiate it in qml. Then i pass this through some qml Page where i populate this object; at last i want to bring this object back to c++ world.
Here is an example: i have this CustomObj

customobj.h:

#include <QObject>
#include <QMetaType>

class CustomObj : public QObject
{
    Q_OBJECT
    Q_PROPERTY(QString name READ name WRITE setName NOTIFY nameChanged)
public:
    explicit CustomObj(QObject *parent = nullptr);
    CustomObj(const CustomObj &other, QObject *parent = nullptr);
    QString name() const { return m_name; }
    void setName(const QString &newName);

signals:
    void nameChanged();

public slots:
private:
    QString m_name;
};

Q_DECLARE_METATYPE(CustomObj)

customobj.cpp:

CustomObj::CustomObj(QObject *parent) : QObject(parent), m_name("test") {
}

CustomObj::CustomObj(const CustomObj &other, QObject *parent) : QObject(parent) {
    m_name = other.name();
}

void CustomObj::setName(const QString &newName) {
    m_name = newName;
}

it has only one attribute m_name setted in the constructor to show the issue.
I use a Manager to manage this object. Here is the code:

manager.h:

#include <QObject>
#include <iostream>

#include "customobj.h"

class Manager : public QObject {

    Q_OBJECT
public:
    explicit Manager(QObject *parent = nullptr);
    Q_INVOKABLE void doSomething(const CustomObj &obj);

signals:
public slots:
};

manager.cpp:

Manager::Manager(QObject *parent) : QObject(parent) {

}

void Manager::doSomething(const CustomObj &obj) {

    std::cout << obj.name().toStdString() << std::endl;
}

not much to say here, just a function to show the problem.
In main.cpp i have registered the two objects:

qmlRegisterType<Manager> ("Manager", 1, 0, "Manager");
qmlRegisterType<CustomObj> ("CustomObj", 1, 0, "CustomObj");

In main.qml i create the manager and start a stackview:

ApplicationWindow {
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")

    Manager {
        id: myManager
    }

    StackView {
        id: stackView

        anchors.fill: parent
        initialItem: FirstView { }
    }
}

In FirstView.qml i create the custom object and set the name attribute as user input:

Page {
    id: root

    TextField {
        id: myText

        anchors.centerIn: parent
    }

    CustomObj {
        id: myCustomObj

        name: myText.text
    }

    Button {
        id: nextButton

        anchors {
            top: myText.bottom
            horizontalCenter: parent.horizontalCenter
            margins: 20
        }

        text: "Next"
        onClicked: {
            console.log(myCustomObj.name)
            root.StackView.view.push("qrc:/SecondView.qml", { myCustomObj: myCustomObj })
        }
    }
}

the output here is obviously correct and show what i have inserted
Here is the SecondView.qml:

Page {
    id: root

    property CustomObj myCustomObj

    Button {
        id: doSomethingButton

        anchors.centerIn: parent
        text: "Do something"
        onClicked: {
            console.log(myCustomObj.name)
            myManager.doSomething(myCustomObj)
        }
    }
}

The output is correct again, but the doSomethingFunction() won't print what i have inserted in TextField, but only "test". Using debugger i have noticed that once i pass myCustomObj to doSomething() method, a new CustomObj is created instead of using the existent one. Any suggestion about this behaviour?
I have found another way to do the same, but i would still understend why this happends.
Thanks!

[raven-worx]

@rigu10 said in Issue creating c++ object in qml and passing it to c++ function:

Q_INVOKABLE void doSomething(const CustomObj &obj);

first thing i noticed is that the signature of your doSomething() method is incorrect.
It should rather take a QObject* parameter. This instance you can then cast to your custom type:

void Manager::doSomething(QObject* obj) {
    if( CustomObj* c = qobject_cast<CustomObj*>(obj) )
          qDebug() << c->name();
}

[rigu10]

@raven-worx Thanks, this solved my problem :)