C++ (Qt)
class A
{
public:
    A() {}
 
protected:
    void mousePressEvent(QMouseEvent* pe)
    {
        qDebug() << Q_FUNC_INFO << "\n";
        if (pe->button() & Qt::LeftButton)
            point = pe->pos();
    }
 
    void mouseMoveEvent(QMouseEvent* pe)
    {
        qDebug() << Q_FUNC_INFO << "\n";
        QWidget *w = self();
        w->move(pe->globalPos() - point);
    }
 
    void keyPressEvent(QKeyEvent* pe)
    {
        if(pe->key() & Qt::Key_Enter)
        {
            start();
        }
    }
 
    void start() { qDebug() << Q_FUNC_INFO << "\n"; }
    QWidget *self() { return 0; }
 
private:
    QPoint point;
};
 
class Widget : public QWidget, public A
{
    Q_OBJECT
public:
    Widget(QWidget *parent = 0) : QWidget(parent), A()
    {
 
    }
 
protected:
    void mousePressEvent(QMouseEvent* pe) { qDebug() << Q_FUNC_INFO; A::mousePressEvent(pe); }
    void mouseMoveEvent(QMouseEvent* pe) { qDebug() << Q_FUNC_INFO; A::mouseMoveEvent(pe); }
    void keyPressEvent(QKeyEvent* pe) { qDebug() << Q_FUNC_INFO; A::keyPressEvent(pe); }
 
    QWidget *self() { return this; }
 
private slots:
    void slotStart() { start(); }
};
 
class Timer : public QLabel, public A
{
    Q_OBJECT
private:
    Widget *wh;
 
private slots:
    void slotStart() { start(); }
 
protected:
    void mousePressEvent(QMouseEvent* pe) { qDebug() << Q_FUNC_INFO; A::mousePressEvent(pe); }
    void mouseMoveEvent(QMouseEvent* pe) { qDebug() << Q_FUNC_INFO; A::mouseMoveEvent(pe); }
    void keyPressEvent(QKeyEvent* pe) { qDebug() << Q_FUNC_INFO; A::keyPressEvent(pe); }
 
    QWidget *self() { return this; }
 
public:
    Timer(QWidget *parent = 0) : QLabel("label", parent), A), wh(new Widget)
    {
        wh->show();
    }
};