Painting the same thing in two subclasses of QPaintDevice

I have a class DotCanvas: public QWidget that shows a pattern of dots. I also have some blank buttons which I'd like to label with dot patterns. So what I'm thinking of doing is making a class DotPixmap: public QPixmap with 256×256 pixel array, draw the patterns on them, load them into the icons, and load the icons into the buttons.

So I try to create a class DotPaintDevice which has the dot-painting code, and subclass DotCanvas from both QWidget and DotPaintDevice. I've done multiple inheritance before, so I figure I can do it, using "using" statements to tell the compiler from which superclass a subclass inherits an ambiguous function, if necessary. I compile it and get this:

Quote:

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/home/phma/src/mirasol/dotcanvas.h:38: Warning: Class DotCanvas inherits from two QObject subclasses QWidget and DotPaintDevice. This is not supported!

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followed by lots of errors. I manage to fix some errors, but there are errors in compiling the moc output, which I haven't a clue what to do with.

So it looks like I have to duplicate the dot-painting code in two classes, one subclass of QWidget and one subclass of QPixmap. For this program the dot-painting code is simple, but how do you do it when you have some complicated stuff to display and you want to display and print the same stuff? Which I will, when I get around to adding the GUI to another program I'm working on.

As the warning you posted says, you can't inherit multiple times a QObject.

Quote:

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but how do you do it when you have some complicated stuff to display and you want to display and print the same stuff? Which I will, when I get around to adding the GUI to another program I'm working on.

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You could make DotPaintDevice not derive form QObject.
There is really no need to as its only doing some specialized painting.

Pseudo code:

Code:

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class DotPaintDevice
{
public:
   DotPaintDevice();
   ~DotPaintDevice();
   void mySpecialPainitingMethod();
};
 
class DotCanvas : public DotPaintDevice, public QWidget
{
   void paintEvent(...)
   {
     .....
     mySpecialPainitingMethod();
     ....
   }
};

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Doesn't DotPaintDevice have to inherit QPaintDevice?

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Doesn't DotPaintDevice have to inherit QPaintDevice?

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No, QWidget inherits QPaintDevice, so the class DotCanvas *is* a QPaintDevice by virtue of multiple inheritance. You will need to pass a pointer or reference to the QPainter used in the paintEvent() to your special paint method.