Sets whether or not the actions within this button should be checkable.
        
        :param      state | <bool>

def setCheckable(self, state):
        """
        Sets whether or not the actions within this button should be checkable.
        
        :param      state | <bool>
        """
        self._checkable = state
        for act in self._actionGroup.actions():
            act.setCheckable(state)