外观模式又称包装外观模式,从字面意思很好理解,即对某一类复杂操作的封装。封装出更直观通用的接口类,然后给客户端调用。比如,你离开家,要关上灯,关上空调,关上电源等,这是一系列很麻烦的操作,因此,你可以把这一系列的操作封装到一个类中,然后让客户端调用。
举例如下:
class Equipment(object):
def __init__(self):
self.name = ''
self.state = 'open'
def turn_off(self):
if self.state == 'closed':
print('%s has been shut down')
else:
self.state = 'closed'
print('%s is closed' % self.name)
class Lamp(Equipment):
def __init__(self):
super().__init__()
self.name = 'lamp'
class AirConditioner(Equipment):
def __init__(self):
super().__init__()
self.name = 'air_conditioner'
class OldClient(object):
def __init__(self, lamp, air_conditioner):
self.lamp = lamp
self.air_conditioner = air_conditioner
def leave_home(self):
self.lamp.turn_off()
self.air_conditioner.turn_off()
class FacadeEquipment(object):
def __init__(self, lamp, air_conditioner):
self.lamp = lamp
self.air_conditioner = air_conditioner
def close(self):
self.lamp.turn_off()
self.air_conditioner.turn_off()
class FacadeClient(object):
def __init__(self, equipments):
self.equipments = equipments
def leave_home(self):
self.equipments.close()
if __name__ == '__main__':
print('old pattern')
lamp = Lamp()
air_conditioner = AirConditioner()
old_client = OldClient(lamp, air_conditioner)
old_client.leave_home()
print('facade pattern')
facade_equipment = FacadeEquipment(lamp, air_conditioner)
facade_client = FacadeClient(facade_equipment)
facade_client.leave_home()
结果如下
old pattern
lamp is closed
air_conditioner is closed
facade pattern
%s has been shut down
%s has been shut down
上述代码实现了lamp,airconditioner类,这两个类继承自equipment,oldclient直接调用了这两个类的实例,耦合性比较强。采用外观模式后,FacadeEquipment对lamp和airconditioner进行了封装,实现了客户端与lamp和airconditioner解耦,同时,FacadeEquipment封装出了close方法,已供新的外观模式客户端调用