Qt emit base class signal from derived class - c++

Question

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 emitting the signal isn't working and I am not able to make the signal static
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();
static int m_seats;
signals:
void updateSeats();
};
car.cpp
#include "car.h"
Car::Car(QObject *parent) :
QObject(parent)
{
}
int Car::m_seats = 0;
Car::~Car(){}
toyota.h
#include "car.h"
class Toyota : public Car{
Q_OBJECT
public:
explicit Toyota(QObject *parent = 0);
~Toyota();
Q_INVOKABLE void foundCar();
};
toyota.cpp
#include "toyota.h"
Toyota::Toyota(QObject *parent)
{
}
Toyota::foundCar(){
m_seats = 4;
emit updateSeats(); // This isn't working
}
Toyota::~Toyota(){}
main.cpp
#include <QGuiApplication>
#include "car.h"
#include "toyota.h"
int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);
Car car = new Car();
Toyota ty = new Toyota();
QQmlApplicationEngine engine;
QQmlContext *ctxt = engine.rootContext();
ctxt->setContextProperty("car", car);
ctxt->setContextProperty("toyota", ty);
engine.load(QUrl(QLatin1String("qrc:/main.qml")));
app.exec();
engine.quit();
}
In qml when I print car.seats after invoking the foundCar function
main.qml
toyota.foundCar()
console.log(car.seats)
the output is still 0. The reason the signal being emitted is not updating is probably because it is from a different object (Toyota). So how can I emit the signal of the base class from the derived class?

Answer 1

Your toyota and car properties are two separate ones.
You have to read the seats property from toyota:
main.qml
toyota.foundCar()
console.log(toyota.seats) //<--- here
Update after comment:
Ok, that's a different approach, but in that case I would set the car property to the toyota pointer:
main.cpp
Car car = new Toyota();
ctxt->setContextProperty("car", ty);
ctxt->setContextProperty("toyota", ty);
This probably can be fitted in a overarching class (something like car_manager or car_store) in which you have a list of available cars and a function to select one car as the current, then you update the generic car or current property of that overarching class.
I say this because you will get nasty code when you want to work from the root context and furthermore, root properties don't signal that they are changed