python_设计模式——责任链模式

python_设计模式——责任链模式

最近编程经常用到责任链模式，在这里简记一下，方便以后再用到回看O(∩_∩)O哈哈~

创建事件的枚举类型 ——注意创建枚举类型的技巧

    ALL_EVENTS = "click","rightmousedown","dbclick","leftmousedown"
    EVENT_DEF = collections.namedtuple("event",ALL_EVENTS)
    EVENTS = EVENT_DEF(*ALL_EVENTS)

事件基类,在这里就用一个不能动态添加属性的字符串表示

    class Event(str):
        __slots__ =()

动态创建类的new方法

    def makeNewMethod(clsName):
        def new(cls):
            return Event.__new__(cls,clsName)
        return new

动态创建定义的事件类，放到全局作用域中

    for clsName in  ALL_EVENTS:
        _new = makeNewMethod(clsName)
        cls = type(clsName,(Event,),dict(__slots__=(),__new__ = _new))
        globals()[clsName] = cls

定义事件基类，采用责任链模式动态处理事件

    class ChainObject(object):

        def __init__(self,successor=None):
            self.successor = successor

        def handle(self,event):
            assert(isinstance(event,Event)) #之所以创建事件类是为了便于我们判断是不是事件
            if self.successor:
                self.successor.handle(event)
            else:
                print("Drop event {} for no handler".format(event))

定义事件类

    class ClickHandler(ChainObject):

        def handle(self,event):
            if event== EVENTS.click:
                print("{} Event handled by:{}".format(event,ClickHandler.__name__))
            else:
                super().handle(event)

    class RightmousedownHandler(ChainObject):

        def handle(self,event):
            if event== EVENTS.rightmousedown:
                print("{} Event handled by:{}".format(event,RightmousedownHandler.__name__))
            else:
                super().handle(event)

主程序：

    if __name__=="__main__":
        #handler Chain
        proessor = ClickHandler(RightmousedownHandler())
        clickEvent = globals()[EVENTS.click]()
        rightmousedownEvent = globals()[EVENTS.rightmousedown]()
        leftmousedownEvent = globals()[EVENTS.leftmousedown]()
        proessor.handle(clickEvent)
        proessor.handle(rightmousedownEvent)
        proessor.handle(leftmousedownEvent)