python设计模式第十天【观察者模式】

1.应用场景

（1）监听事件驱动程序中的外部事件

（2）监听某个对象的状态变化

（3）发布-订阅模型中，消息出现时通知邮件列表中的订阅者

2. 观察者模式UML图

3. 代码实现：

#!/usr/bin/env python
#! _*_ coding:UTF-8 _*_

from abc import ABCMeta, abstractmethod

class Subject(object):

    def __init__(self):
        '''初始化监听器列表'''
        self.__observerList = []

    def registerObserver(self, observer):
        '''注册一个监听器对象'''
        self.__observerList.append(observer)

    def unregisterObserver(self, observer):
        '''解除注册一个监听器对象'''
        self.__observerList.remove(observer)

    def notifyObservers(self):
        '''通知监听器对象'''
        for observer in self.__observerList:
            observer.notify()

class ConcreteSubject(Subject):

    def action(self):
        print "action"
        self.notifyObservers()

class Observer(object):

    @abstractmethod
    def notify(self):
        pass

class ConcreteObserverA(Observer):

    def notify(self):
        print "notify of observer A"

class ConcreteObserverB(Observer):

    def notify(self):
        print "notify of observer B"

if __name__ == "__main__":
    concreteSubject = ConcreteSubject()

    concreteObserverA = ConcreteObserverA()
    concreteObserverB = ConcreteObserverB()

    concreteSubject.registerObserver(concreteObserverA)
    concreteSubject.registerObserver(concreteObserverB)

    concreteSubject.action()

结果：

/Users/liudaoqiang/PycharmProjects/numpy/venv/bin/python /Users/liudaoqiang/Project/python_project/day10_observer/observer_test.py
action
notify of observer A
notify of observer B

Process finished with exit code 0