問題描述

我意識到這個問題與事件處理有關，并且我已經閱讀了有關 Python 事件處理程序和調度程序的信息，所以要么它沒有回答我的問題，要么我完全錯過了信息.

I realise this question has to do with event-handling and i've read about Python event-handler a dispatchers, so either it did not answer my question or i completely missed out the information.

我希望在值 v 發生變化時觸發對象 A 的方法 m():

I want method m() of object A to be triggered whenever value v is changing:

例如(假設金錢使人快樂):

For instance (assuming money makes happy):

global_wealth = 0

class Person()
    def __init__(self):
        self.wealth = 0
        global global_wealth
        # here is where attribute should be
        # bound to changes in 'global_wealth'
        self.happiness = bind_to(global_wealth, how_happy)

    def how_happy(self, global_wealth):
        return self.wealth / global_wealth

因此，每當 global_wealth 值更改時，Person 類的所有實例都應相應更改其 happiness 值.

So whenever the global_wealth value is changed, all instances of the class Person should change their happiness value accordingly.

NB:我不得不編輯這個問題，因為第一個版本似乎表明我需要 getter 和 setter 方法.很抱歉造成混亂.

NB: I had to edit the question since the first version seemed to suggest i needed getter and setter methods. Sorry for the confusion.

推薦答案

你需要使用 觀察者模式.在以下代碼中，一個人訂閱接收來自全球財富實體的更新.當全球財富發生變化時，該實體會提醒其所有訂閱者(觀察者)發生變化.Person 然后更新自己.

You need to use the Observer Pattern. In the following code, a person subscribes to receive updates from the global wealth entity. When there is a change to global wealth, this entity then alerts all its subscribers (observers) that a change happened. Person then updates itself.

我在這個例子中使用了屬性，但它們不是必需的.一個小警告:屬性僅適用于新樣式類，因此類聲明后的 (object) 是強制性的.

I make use of properties in this example, but they are not necessary. A small warning: properties work only on new style classes, so the (object) after the class declarations are mandatory for this to work.

class GlobalWealth(object):
    def __init__(self):
        self._global_wealth = 10.0
        self._observers = []

    @property
    def global_wealth(self):
        return self._global_wealth

    @global_wealth.setter
    def global_wealth(self, value):
        self._global_wealth = value
        for callback in self._observers:
            print('announcing change')
            callback(self._global_wealth)

    def bind_to(self, callback):
        print('bound')
        self._observers.append(callback)


class Person(object):
    def __init__(self, data):
        self.wealth = 1.0
        self.data = data
        self.data.bind_to(self.update_how_happy)
        self.happiness = self.wealth / self.data.global_wealth

    def update_how_happy(self, global_wealth):
        self.happiness = self.wealth / global_wealth


if __name__ == '__main__':
    data = GlobalWealth()
    p = Person(data)
    print(p.happiness)
    data.global_wealth = 1.0
    print(p.happiness)

這篇關于如何觸發價值變化的功能?的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！