Question

I’m studying the Qt4 library and I want to add some functionality to all the children of QWidget in my project. I need all widgets to have mousePressEvent overridden. Obviously I do not need to override it in every particular widget I use(I use many of them and I they to follow DRY rule) , instead I create a Foo class:

class Foo : public QWidget
{
    Q_OBJECT
    protected:

        /* implementation is just a test */
        virtual void mousePressEvent(QMouseEvent*) { this->move(0,0);  }
};

And derive my button from it:

class FooButton : public QPushButton , public Foo
{

    public:
        FooButton (QWidget* parent) : QPushButton(parent) { };

};

But the event seems to be not overridden… What am I doing wrong?
Thanks in advance.

Answer 1

You are inheriting twice now from QWidget. This is problematic (see diamond problem).

Instead, drop your Foo class and move your custom mouse press event handler to your FooButton class:

class FooButton : public QPushButton
{
    Q_OBJECT
protected:

    /* implementation is just a test */
    virtual void mousePressEvent(QMouseEvent*) { this->move(0,0);  }

public:
    FooButton (QWidget* parent) : QPushButton(parent) { };

};

If this doesn’t suit the design of your application, then try using virtual inheritance instead. That is, change Foo to:

class Foo : public virtual QWidget

If that doesn’t help, you should follow the advice of the other answers and install an event handler.

(You can read about virtual inheritance in its Wikipedia article.)