CODEWITHSUNDEEP
c++qtqml
blessedone
blessedone

Reputation: 170

Qml not receiving updated value of member variable of base class

I basically just want to use multiple derived classes to change a member variable of a base class and to forward that value to qml using qproperty, but for some reason it's not working

car.h

    #include <QObject>

    class Car : public QObject{
        Q_OBJECT
        Q_PROPERTY(int seats MEMBER m_seats NOTIFY updateSeats)

    public:
        explicit Car(QObject *parent = 0);
        ~Car();
        int m_seats;
        Q_INVOKABLE void test();

    signals:
        void updateSeats();
    };

car.cpp 

    #include "car.h"

    Car::Car(QObject *parent) :
        QObject(parent),
        m_seats(0)
    {

    }

    Car::test(){
        m_seats = 5;
        emit updateSeats();
    }

    Car::~Car(){}

toyota.h

    #include "car.h"

    class Toyota : public Car{
        Q_OBJECT


    public:
        explicit Toyota(QObject *parent = 0);
        ~Toyota();
        void foundCar();
    };

toyota.cpp 

    #include "toyota.h"

    Toyota::Toyota(QObject *parent) 
    {

    }

    Toyota::foundCar(){
        m_seats = 4;
        emit updateSeats();
    }

    Toyota::~Toyota(){}

Now, after invoking the foundCar function in class Toyota, if I do console.log(car.seats) in qml I get 0, but I expect it to be 4 because I am modifying it in the derived class. However if I call car.test() from qml and then I print car.seats, the value is 5. I am confused why this is the case. In qml I want car.seats to be 4. What am I missing?

Upvotes: 0

Views: 348

Answers (1)

Mohammad Kanan
Mohammad Kanan

Reputation: 4582

Toyota object is derived class object Toyota of base Car not an object of Car you are modifying derived class object member Toyota::m_seats and that won't have any effect on direct base Car object .. and because Q_PROPERTY is defined only in base class Car .. the only value QML would see is base class object .. and specifically the object you set in setContextProperty ... the code you omitted after the post edit.

From previous edits in your post, you seem to set the setContextProperty in your engine as Car object .. its in this object where you need to modify member that is a Q_PROPERTY.

I am referring to your code:

Car::startGui(){
    QQmlApplicationEngine engine;
    QQmlContext *ctxt = engine.rootContext();
    ctxt->setContextProperty("car", this)
    // start engine, which works properly
}

Upvotes: 1

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