Access to nested c++ objects in QML?

Alien

Hey,
Imagine you have a page that it contains one or more menus and each menus has one or more keys inside and each keys has its features, how to export it into QML in a way all of nested objects inside higher level class be accessible?

I've tried inheritance from QObject and using QVector to store variable number of nested objects but I faced to a lots of problems.

For instance I want to access to keys feature with something like below snippet code:

Rectangle
{
width:100
height:100
color:"red"
Text{
anchors{centerIn:parent}
text:CPM.CPage[0].CMenus[0].CKeys[0].Name
}
}

Yours,
Ali

raven-worx

@Alien said in Access to nested c++ objects in QML?:

I've tried inheritance from QObject and using QVector to store variable number of nested objects but I faced to a lots of problems.

What were your problems?
Also you should use QVariantList and/or QVariantMap instead. See here.

Alien

Dear @raven-worx ,

In fact the problem is something ridiculous, I don't expect that something like this become a problem to me!
By the way could you please have a look at the below code :

Key Header:

#ifndef CKEY_H
#define CKEY_H

#include <QObject>
#include <QColor>
#include <QString>

class CKey:public QObject
{
Q_OBJECT
    Q_PROPERTY(QString Name READ name WRITE setName NOTIFY nameChanged)
    Q_PROPERTY(int Number READ number WRITE setNumber NOTIFY numberChanged)
    Q_PROPERTY(QColor Color READ color WRITE setColor NOTIFY colorChanged)
private:
    QString m_name;
    int m_number;
    QColor m_color;
public:
    CKey(QObject *parent=nullptr);

    QString name() const;
    void setName(const QString &name);
    int number() const;
    void setNumber(int number);
    QColor color() const;
    void setColor(const QColor &color);

    ~CKey();
signals:
    void nameChanged();
    void numberChanged();
    void colorChanged();
};

#endif // CKEY_H

Key source file :

#include "ckey.h"


/*=========================SETTER/GETTER================================*/
QString CKey::name() const
{
    return m_name;
}

void CKey::setName(const QString &name)
{
    m_name = name;
    emit nameChanged();
}

int CKey::number() const
{
    return m_number;
}

void CKey::setNumber(int number)
{
    m_number = number;
    emit numberChanged();
}

QColor CKey::color() const
{
    return m_color;
}

void CKey::setColor(const QColor &color)
{
    m_color = color;
    emit colorChanged();
}


/*=====================================================================*/
CKey::CKey(QObject *parent):QObject(parent)
{
    m_color = Qt::red;
    m_number = 0;
    m_name="default";

}
/*=====================================================================*/

/*=====================================================================*/
CKey::~CKey()
{

}
/*=====================================================================*/

Menu Header:

#ifndef CMENU_H
#define CMENU_H

#include <QObject>
#include <QString>
#include <QVector>
#include "ckey.h"

class CMenu : public QObject
{
    Q_OBJECT
    Q_PROPERTY(QString Name READ name WRITE setName NOTIFY nameChanged)
    Q_PROPERTY(QVector<CKey> KeysList READ keysList WRITE setKeysList NOTIFY keysListChanged)
private :
    QString m_name;
    QVector<CKey> m_keysList;

public:
    explicit CMenu(QObject *parent = nullptr);
    ~CMenu();

    QString name() const;
    void setName(const QString &name);

    QVector<CKey> keysList() const;
    void setKeysList(const QVector<CKey> &keysList);

signals:
    void nameChanged();
    void keysListChanged();

public slots:
};

#endif // CMENU_H

Menu source file:

#include "cmenu.h"

QString CMenu::name() const
{
    return m_name;
}

void CMenu::setName(const QString &name)
{
    m_name = name;
}

QVector<CKey> CMenu::keysList() const
{
    return m_keysList;
}

void CMenu::setKeysList(const QVector<CKey> &keysList)
{
    m_keysList = keysList;
}

CMenu::CMenu(QObject *parent) : QObject(parent)
{

}

CMenu::~CMenu()
{
    if(m_keysList.length()>0)
        m_keysList.clear();

}

And finally main:

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include "ckey.h"
#include "cmenu.h"

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

    CKey key[5];

    key[0].setName("One");
    key[1].setName("TWO");
    key[2].setName("THREE");
    key[3].setName("FOUR");
    key[4].setName("FIVE");

    CMenu menu;

    for (int index = 0; index < 5; ++index)
    {
            menu.keysList().append(key[index]);
    }
#if defined(Q_OS_WIN)
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
#endif

    QGuiApplication app(argc, argv);
    QQmlApplicationEngine engine;
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
    if (engine.rootObjects().isEmpty())
        return -1;
    QQmlContext * context=engine.rootContext();
    context->setContextProperty("CMenu",&menu);
    return app.exec();
}

Compile Errors:
error: use of deleted function 'CKey& CKey::operator=(const CKey&)'
use of deleted function 'CKey::CKey(const CKey&)'
Of course these errors say to me that CKey need to implement operator = and CKey(const CKey&) but why?Does it have any better way to doing that?

raven-worx

@Alien said in Access to nested c++ objects in QML?:

QVector<CKey>

The errors are because you use a QObject derived class a reference/copy type. This is not allowed. QObject must be allocated on the heap (=pointers).
So change your declaration and properties to QList<CKey*>

Alien

Dear @raven-worx,
I changed the CMenu class to below:

Header

#ifndef CMENU_H
#define CMENU_H

#include <QObject>
#include <QString>
#include <QVector>
#include "ckey.h"

class CMenu : public QObject
{
    Q_OBJECT
    Q_PROPERTY(QString Name READ name WRITE setName NOTIFY nameChanged)
    Q_PROPERTY(QList<CKey*> KeysList READ keysList NOTIFY keysListChanged)
private :
    QString m_name;
    QList<CKey*> m_keysList;

public:
    explicit CMenu(QObject *parent = nullptr);
    ~CMenu();

    QString name() const;
    void setName(const QString &name);
    void addKey(CKey* key);

    QList<CKey*> keysList() const;

signals:
    void nameChanged();
    void keysListChanged();

public slots:
};

#endif // CMENU_H

source

#include "cmenu.h"

QString CMenu::name() const
{
    return m_name;
}

void CMenu::setName(const QString &name)
{
    m_name = name;
}

void CMenu::addKey(CKey *key)
{
    m_keysList.append(key);
}

QList<CKey *> CMenu::keysList() const
{
    return m_keysList;
}



CMenu::CMenu(QObject *parent) : QObject(parent)
{

}

CMenu::~CMenu()
{
    if(m_keysList.length()>0)
        m_keysList.clear();

}

and main.cpp:

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include "ckey.h"
#include "cmenu.h"

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

    CKey *key = new CKey[5];

    key[0].setName("One");
    key[1].setName("TWO");
    key[2].setName("THREE");
    key[3].setName("FOUR");
    key[4].setName("FIVE");

    CMenu menu;
    menu.setName("Test");

    for (int index = 0; index < 5; ++index)
    {
        menu.addKey(&key[index]);
    }


#if defined(Q_OS_WIN)
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
#endif

    QGuiApplication app(argc, argv);
    QQmlApplicationEngine engine;
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
    if (engine.rootObjects().isEmpty())
        return -1;
    QQmlContext * context=engine.rootContext();
    context->setContextProperty("CMenu",&menu);
    return app.exec();
}

it build correctly now how to access to keys from qml:

import QtQuick 2.10
import QtQuick.Window 2.10

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


    Rectangle
    {
        width:150
        height: 150
        color: "yellow"
        Text {
            id: txtID
            text: qsTr(CMenu.KeysList.at(0).Name)
        }
    }
}

Errors:

qrc:/main.qml:18: ReferenceError: CMenu is not defined
qrc:/main.qml:18: TypeError: Property 'at' of object QVariant(QVector<CKey*>) is not a function

How to access to CKey's attributes from Cmenu in QML?

raven-worx

@Alien said in Access to nested c++ objects in QML?:

How to access to CKey's attributes from Cmenu in QML?

When you just want to read values:

CMenu {
    id: cm
}
...
cm.KeysList[0].Name