观察者模式 Python版--第14章

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双向耦合的代码

class Secretary:    observers = []action = None    def Attach(self, observer):        self.observers.append(observer)    def Notify(self):        for o in observers:            o.Update()    def SecretaryAction(self, value):self.action = value        return self.actionclass StockObserver:    def __init__(self, name , sub):        self.name = name        self.sub = sub    def Update(self)：        print self.sub.SecretaryAction,self.name, "close stock, keep working"if __name__ == "__main__":    s = Secretary()    c1 = StockObserver("xiaohua", s)    c2 = StockObserver("xiaoli", s)    s.Attach(c1)    s.Attach(c2)    s.SecretaryAction("Boss is coming!")    s.Notify()

解耦合实践---增加了抽象的观察者

class Observer:    def __init__(self, name, sub):    self.name = nameself.sub = subdef Update(self):    print sub.SecretaryAction,self.nameclass StockObserver(Observer):    def __init__(self, name, sub):        Observer.__init__(name, sub)    def Update(self):        print "stop stock, keep working"    class NBAObserver(Observer):    def __init__(self, name, sub):        Observer.__init__(name, sub)        def Update(self):        print "stop watching NBA, keep working"

观察者模式（发布-订阅模式）

class Subject:    observers = []    def Attach(self, observer): self.observers.append(observer)    def Detach(self, observer):        self.observers.remove(observer)       def Notify(self)        for o in self.observers:            o.Update()class ConcreteSubject(Subject):    subjectState = None    def SetSubjectState(self, state):        self.subjectState = state    def GetSubjectState(self):        return self.subjectState    def SubjectState(self, state):        self.SetSubjectState(state)        self.GetSubjectState()class Observer:    def Update(self): passclass ConcreteObserver(Observer):    def __init__(self, sub, name):        self.sub = sub        self.name = name    def Update(self):        self.state = self.sub.subjectState        print "the new state of observer is ", self.state    def SetState(self, state):        self.state = state    def GetState(self):        return self.state    def Subject(self, state):        self.SetState(state)        self.GetState()if __name__ =="__main__":    s = ConcreteSubject()    s.Attach(ConcreteObserver(s,"X"))    s.Attach(ConcreteObserver(s,"Y"))     s.Attach(ConcreteObserver(s,"Z"))     s.SubjectState = "ABC"    s.Notify()

一个抽象模型有两个方面，其中一个方面依赖于另一方面，这时用观察者模式可以将这两者封装在独立的对象中使它们各自独立地改变和复用。

观察者模式所做的工坐其实就是在解除耦合。让耦合的双方都依赖于抽象，而不是依赖于具体。从而使得各自的变化都不会影响到另一边的变化。

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