How to update the components or repaint of a QMainWindow?

[ChrisW67]

Yes, in the header for Window:

class Window: public QMainWindow
{
  Q_OBJECT
public:
  Window(...);
 
...
private slots:  //
  void modify();
...
};

class Window: public QMainWindow
{
  Q_OBJECT
public:
  Window(...);

...
private slots:  //
  void modify();
...
};

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and you must rerun qmake if you added the Q_OBJECT macro.