如何触发价值变动的功能？ [英] How to trigger function on value change?

问题描述

我意识到这个问题与事件处理有关，我已经阅读了Python事件处理程序的调度程序，所以它没有回答我的问题，或者我完全错过了这些信息。

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.

我想要方法 m（）对象 A 每当值 v 正在变化：

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

例如（假设钱开心）：

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

所以每当 global_wealth 值更改，类 Person 的所有实例应更改其 happines

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

注意：我不得不编辑这个问题，因为第一个版本似乎建议我需要吸气剂和固定剂的方法。对不起，感到困惑。

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

推荐答案

你需要使用，rel =noreferrerwikipedia.org/wiki/Observer_pattern。
在下面的代码中，一个人订阅从全球财富实体接收更新。当全球财富发生变化时，该实体会向所有订阅者（观察员）发出更改。然后人们进行更新。

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.

在本示例中，我利用属性，但不是必需的。一个小小的警告：属性只适用于新的样式类，所以（对象）在类声明之后是强制性的。

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 = []

    def get_wealth(self):
        return self._global_wealth

    def set_wealth(self, value):
        self._global_wealth = value
        for callback in self._observers:
            print 'anouncing change'
            callback(self._global_wealth)

    global_wealth = property(get_wealth, set_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

这篇关于如何触发价值变动的功能？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！