QObject Multiple Inheritance

Question

I am trying to use mix in classes for C++/Qt to provide a whole bunch of widgets with a common interface. The interface is defined in such as way so that if it is defined as

Answer 1

Unfortunately inheriting QObject twice will cause problems in moc.

From http://qt-project.org:

If you are using multiple inheritance, moc assumes that the first inherited class is a subclass of QObject. Also, be sure that only the first inherited class is a QObject.

I would suggest using something more like the delegate pattern, or recreate with a HasA not a IsA relationship.

Answer 2

Qt allows multiple inheritance if the base class inherits privately from QObject.

Example:

class Base: private QObject {
   Q_OBJECT
   /*Can use signals and slots like any other QObject-derived class*/
};

class Derived1: public Base {
   /*Cannot use signals/slots because it does not "see" that Base inherits from QObject*/
};

class Derived2: public QWidget, public Base {
   Q_OBJECT
   /*Can use signals/slots plus has all the functionality of QWidget and Base*/
};

Of course, private inheritance is a different animal altogether and may not give you the solution you really need. What I use it for is when I can get away with using signals/slots only in the base class. When I really do need QObject behavior in a derived class, I inherit from QObject specifically for just that class.