當允許一個對象在其內部狀態發生變化後改變它的行爲,可以藉助狀態模式實現。
實現方法:
定義一個抽象狀態類,添加對應的methods(行爲),讓不同的狀態繼承自這個抽象狀態類,同時重寫對應的methods(行爲),這樣就構建了不同的狀態。
接下來讓狀態的主體與狀態間構成組合關係,即狀態是主體的一部分,利用self.state = State()實現,同時,將主體與狀態進行關聯,以達到執行不同狀態行爲的能力。
UML類圖
簡單代碼
# TODO: 抽象的狀態類
class State:
# 獲取狀態的名稱
def getName(self):
pass
# 不同狀態下的不同行爲
def behavior(self):
pass
class SolidState(State):
def getName(self):
return "Solid"
def behavior(self):
print("水變成了固態")
class LiquidState(State):
def getName(self):
return "Liquid"
def behavior(self):
print("水變成了液態")
class GaseousState(State):
def getName(self):
return "Liquid"
def behavior(self):
print("水變成了氣態")
class Water:
def __init__(self):
self.__temperature = 25
self.__state = LiquidState()
def behavior(self):
self.__state.behavior()
def setState(self):
if self.__temperature >=100:
self.__state = GaseousState()
elif self.__temperature>=0:
self.__state = LiquidState()
else:
self.__state = SolidState()
# 下面的是針對這個例子添加的methods
def getTemperature(self):
return self.__temperature
def increaseTemperature(self, step):
self.__temperature += step
self.setState()
self.behavior()
def decreaseTempearature(self, step):
self.__temperature -= step
self.setState()
self.behavior()
if __name__ == '__main__':
waterIns = Water()
waterIns.increaseTemperature(78)
waterIns.decreaseTempearature(120)
上面的代碼實際上並不好,這裏不做說明了。
看了網上的對狀態模式的代碼,有一個地方覺得挺有意思,就是狀態切換的實現,是放到子狀態中實現,即子狀態中定義setState()方法(接下來的代碼),還是放到主體類的methods中(上面的代碼),兩種情況都有出現過。
class State(object):
13 def __init__(self):
14 pass
15
16 def write_program(self, w):
17 pass
18
19 class Work(object):
20
21 def __init__(self):
22 self.hour = 9
23 self.curr = ForenoonState()
24
25 def set_state(self, s):
26 self.curr = s
27
28 def write_program(self):
29 self.curr.write_program(self)
30
31
32 class ForenoonState(State):
33
34 def write_program(self, w):
35 if w.hour < 12:
36 print "當前時間:%s點,"%w.hour,"精神百倍"
37 else:
38 w.set_state(AfternoonState())
39 w.write_program()
40
41 class AfternoonState(State):
42
43 def write_program(self, w):
44 if w.hour < 17:
45 print "當前時間:%s點,"%w.hour,"狀態還行,繼續努力"
46 else:
47 w.set_state(EveningState())
48 w.write_program()
49
50 class EveningState(State):
51
52 def write_program(self, w):
53 if w.hour < 21:
54 print "當前時間:%s點,"%w.hour,"加班呢,疲勞了"
55 else:
56 w.set_state(SleepState())
57 w.write_program()
58
59
60 class SleepState(State):
61
62 def write_program(self, w):
63 print "當前時間:%s點,"%w.hour,"不行了,睡着了"
64
65 if __name__=="__main__":
66 work = Work()
67 work.hour = 9
68 work.write_program()
69 work.hour = 15
70 work.write_program()
71 work.hour = 20
72 work.write_program()
73 work.hour = 22
74 work.write_program()
按照前面的UML圖,我更傾向將狀態切換的method放到主體類中。
完善一下
具體怎麼完善,人人都懂設計模式中有,後續補充