def on_button_press(self, event):
        """Handle button press events.

        If the (mouse) button is pressed on top of a Handle (item.Handle), that handle is grabbed and can be
        dragged around.
        """
        if not event.get_button()[1] == 1:  # left mouse button
            return False
        view = self.view

        item, handle = HandleFinder(view.hovered_item, view).get_handle_at_point((event.x, event.y))

        if not handle:  # Require a handle
            return False

        # Connection handle must belong to a port and the MOVE_PORT_MODIFIER must not be pressed
        if not isinstance(item, StateView) or handle not in [port.handle for port in item.get_all_ports()] or (
                    event.get_state()[1] & constants.MOVE_PORT_MODIFIER):
            return False

        for port in item.get_all_ports():
            if port.handle is handle:
                self._start_port_v = port
                if port in item.get_logic_ports():
                    self._is_transition = True
                if port is item.income or isinstance(port, InputPortView) or port in item.scoped_variables:
                    self._parent_state_v = port.parent
                elif port.parent.parent:
                    self._parent_state_v = port.parent.parent
                else:  # Outgoing port of the root state was clicked on, no connection can be drawn here
                    self._parent_state_v = None

        return True