Subclassing a widget created in Qt Designer

[dmginc]

I have a QLabel within my Qt Designer-created MainWindow.

However, I would like to add mouse tracking to this QLabel by subclassing QLabel and creating a new class called QLabelWithMouseTracking which will contains re-implementations of the appropriate protected functions: mousePressEvent(), mouseReleaseEvent() etc.

My question is:

How do I perform the subclassing and create a new class given that this QLabel is already created and initialized in the Designer UI header file?

Also, I'm using the multi-inheritance approach. i.e.

#include "ui_MainWindow.h"
 
class MainWindow : public QMainWindow, private Ui::MainWindow
{
    Q_OBJECT
 
public:
    MainWindow(QWidget *parent = 0);
};

#include "ui_MainWindow.h"

class MainWindow : public QMainWindow, private Ui::MainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = 0);
};

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etc.

Thanks in advance to anyone who can steer me in the right direction!