Reading deeper into the docs, QGestureRecognizer is needed only if you are implementing custom gestures. QWidget::grabGesture() should be all you need for standard gesture support.

Try modifying one of the Qt Graphics / View examples to add grabGesture support to the view widget, see what happens. Or modify a dialog-based example to add grabGesture to the dialog class. You should then be able to tap buttons, I think. I don't have a gesture input device, so I can't try it.