How to disable scroll function when Ctrl is pressed in QMainWindow

Question

I currently works on QT for my project. I implemented a MainWindow class which inherited from QMainWindow.

In MainWindow, I handled mouse wheel event like this:

void MainWindow::wheelEvent ( QWheelEvent * event )
{
   if (event->modifiers().testFlag(Qt::ControlModifier)) {
      if (event->delta() > 0) {
        zoomInAct();
      }
      else if(event->delta()<0){
        zoomOutAct();
      }
  }
}

The problem is: when I press CONTROL KEY and Wheel the mouse, the scroll bar alway scroll to top or bottom before reach my wheelEvent function. Would you please help to allow zoom-in/out when press control and wheel the mouse? (Not scroll the scroll bar)

Sorry for my bad english.

Answer 1

Looking at your current implementation here you have not specified event->accept() if you have added your own functionality and you don't want to propagate the event further to the parent. Try adding event->accept() in the if conditions where you have added your logic.

And try adding debug statement to test whether the event is reaching here or someone else is handling the event. By someone else I mean some other child widget. Some description of the UI and what widget is to be zoomed in would be helpful to further investigate the problem.

Make sure you read about the event system in Qt. Docs available here

Answer 2

Acctualy, there is a child widget that handle the wheel event first (default event handle is scroll the scrollbar).

Solution: override wheelevent in child widget to send it to parent widget (MainWindow) when the control key is pressed.

class WorkArea: public QWidget {
...
  virtual void wheelEvent(QWheelEvent *event)
  {
    if(event->modifiers().testFlag(Qt::ControlModifier))
      MainWindow::wheelEvent(event);
    else
      QWidget::wheelEvent(event);
  }
...
}