Qt signals & inheritance question

inheritanceqtsignals-slotssubclass

I am relatively new to programming with Qt and had a question. Short version:

How do I inherit signals defined in superclasses?

I am trying to subclass someone else's nicely made QTWidgets to change some of the default behavior:


//Plot3D is a QWidget that defines a signal "rotationChanged"
class matLinePlot : public QObject, public Plot3D {

    Q_OBJECT;
        //etc...
public:
       //etc...

        //Catch Plot3D's signal "rotationChanged" and do some magic with it:
    void initPlot(){
              QObject::connect(this, SIGNAL(rotationChanged( double , double , double )),
            this, SLOT(myRotationChanged(double, double, double)));
    }
};

The problem is in the QObject::connect line. What I would like to do is connect the rotationChanged SIGNAL (from qwt3D_plot.h) to a local function/SLOT – "myRotationChanged". However whenever I do this, at run time I get:

Object::connect: No such signal matLinePlot::rotationChanged(double, double, double)

in C:…\matrixVisualization.h. Of course, I know that rotationChanged isn't in matrixVisualization.h – it's in qwt_plot3D.h, but I thought that since I inherit from Plot3D everything should be fine. But, now that I think about it, since SIGNAL and SLOT are macros, I assume MOC doesn't know/care about inheritance.

Which leads me to my question – since MOC and SIGNALS / SLOTS don't seem to know about inheritance etc: how can I subclass a widget defined somewhere else and get access to the widget's signals?

I have a lot of examples of how to use encapsulation to accomplish something like this, but I'm afraid I don't understand how to do this with inheritance.

Sorry if this is a ridiculous question – I feel like I'm missing something obvious.

Best Answer

I guess the problem is the multiple inheritance:

class matLinePlot : public QObject, public Plot3D
...

I assume that Plot3D is a subclass of QObject? In this case, you should do

class matLinePlot : public Plot3D
...

instead.

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