[Solved] Subclassing from QObject base and non Qobject base classes

moravas

Hi Folks,

I have the following architecture:

@
class nativeBase {
protected: nativeBase();
... some stuff...
}

class nativeDerived: public nativeBase {
protected: nativeDerived();
... some stuff...
}
@

Please consider the protected constructor due to prevent the anauthorized creation, and the fact, that there is no Qt specific stuff, like signals or slots...

@
class qobjectBase: public QObject {
Q_OBJECT

... some Qt signals and slots...
protected: qobjectBase();
... some stuff...
}
@

Lets consider the protected constructor, as above and there are some signals and / or slots.

@
class surface: public qobjectBase, public nativeDerived {
Q_OBJECT
}
@

During compilation, I get an error, that there are no qt_metatype(), and other methods which are included by the Q_OBJECT macro whitin the nativeDerived class. It is true, because I don't introduce it. I investigated that I derived the nativeBase from QObject, but in this case, I get an error, that multiple inheritance from QObject is prohibited.

The question is: how can I solve this issue? Maybe, is any solution to tell to Qt, that this is not needed to iterate over the "native" inheritance chain?

Regards,
Norbert

jeremy_k

Can you provide more details? This test based on your example builds and runs for me:

@#include <QObject>
#include <cstdio>

class nativeBase {
protected: nativeBase(){}
};

class nativeDerived: public nativeBase {
protected: nativeDerived(){}
};

class qobjectBase: public QObject {
Q_OBJECT

protected: qobjectBase(){}
};

class surface: public qobjectBase, public nativeDerived {
Q_OBJECT
signals:
void sig();
public slots:
void slot(){ printf("slot!\n"); }
};

int main(int argc, char *argv[])
{
Q_UNUSED(argc);
Q_UNUSED(argv);
surface s;
QObject::connect(&s,&surface::sig, &s, &surface::slot);
emit s.sig();
return 0;
}

#include "main.moc"@

Regarding deriving a class from multiple classes that inherit QObject, that's the diamond inheritance problem. http://en.wikipedia.org/wiki/Multiple_inheritance#The_diamond_problem

SGaist

Hi,

The diamond problem is not really applicable here since you can't inherit multiple times from QObject.

moravas

[quote author="jeremy_k" date="1409428351"]Can you provide more details? This test based on your example builds and runs for me:

@#include <QObject>
#include <cstdio>

class nativeBase {
protected: nativeBase(){}
};

class nativeDerived: public nativeBase {
protected: nativeDerived(){}
};

class qobjectBase: public QObject {
Q_OBJECT

protected: qobjectBase(){}
};

class surface: public qobjectBase, public nativeDerived {
Q_OBJECT
signals:
void sig();
public slots:
void slot(){ printf("slot!\n"); }
};

int main(int argc, char *argv[])
{
Q_UNUSED(argc);
Q_UNUSED(argv);
surface s;
QObject::connect(&s,&surface::sig, &s, &surface::slot);
emit s.sig();
return 0;
}

#include "main.moc"@

Regarding deriving a class from multiple classes that inherit QObject, that's the diamond inheritance problem. http://en.wikipedia.org/wiki/Multiple_inheritance#The_diamond_problem[/quote]

Hi,

I think, you are a bit confused: there are no signals and / or slots whitin the surface class. The signals and / or slots are only defined and implemented in the qobjectBase class, but in order to use their in connect() method, I use those via the surface class.

moravas

[quote author="SGaist" date="1409433572"]Hi,

The diamond problem is not really applicable here since you can't inherit multiple times from QObject.[/quote]

Hi,

yes, you are right, it is not an exactly diamond problem

jeremy_k

[quote author="moravas" date="1409482210"]
Hi,

I think, you are a bit confused: there are no signals and / or slots whitin the surface class. The signals and / or slots are only defined and implemented in the qobjectBase class, but in order to use their in connect() method, I use those via the surface class.[/quote]

Great. So post an example that demonstrates your problem.

moravas

Hi,

this is the concrete architecture:
@
class nativeBase {
public: virtual ~nativeBase();

protected: nativeBase();

protected: QSettings _cfg;
};

class nativeDerived: public nativeBase {

public: virtual ~nativeDerived();

protected: nativeDerived();

private: QString _processName;
};

class qobjectBase: public QObject {
Q_OBJECT

public: virtual ~qobjectBase();

signals: void sigChanged();

public slots: void onNew(const QString& name);
public slots: void onOpen(const QString& name);
public slots: void onDelete(const QString& name);
public slots: void onSaveAs(const QString& name);

protected: qobjectBase();
};

class surface: public nativeDerived, public qobjectBase {
Q_OBJECT
};
@

Regards,
Norbert

jeremy_k

Moc assumes that the QObject derived class comes first in the order of inheritance.

http://qt-project.org/doc/qt-5/moc.html#multiple-inheritance-requires-qobject-to-be-first

moravas

Hi,

thanks a lot!!! It seems to be helpful.

Bye