Filters events for the popup widget.
        
        :param      object | <QObject>
                    event  | <QEvent>

def eventFilter(self, object, event):
        """
        Filters events for the popup widget.
        
        :param      object | <QObject>
                    event  | <QEvent>
        """
        # popup the editor when clicking in the line edit for a checkable state
        if object == self.lineEdit() and self.isEnabled():
            if not self.isCheckable():
                return super(XComboBox, self).eventFilter(object, event)
            
            # show the popup when the user clicks on it
            elif event.type() == event.MouseButtonPress:
                self.showPopup()
            
            # eat the wheel event when the user is scrolling
            elif event.type() == event.Wheel:
                return True
            
        # make sure we're looking for the checkable popup
        elif object == self._checkablePopup:
            if event.type() == event.KeyPress and \
                 event.key() in (Qt.Key_Escape, Qt.Key_Return, Qt.Key_Enter):
                object.close()
            
            elif event.type() == event.MouseButtonPress:
                if not object.geometry().contains(event.pos()):
                    object.close()
        
        return super(XComboBox, self).eventFilter(object, event)