在iOS库类的现有属性上添加属性观察器 [英] Add a property observer on an existing property in an iOS library class

问题描述

在我的SpriteKit游戏中，我想在我的Sprite的SKPhysicsBody的fieldBitMask属性上添加一个属性观察器.我想在fieldBitMask属性更改时得到通知，以便我可以采取一些措施.

In my SpriteKit game, I want to add a property observer on the fieldBitMask property for the SKPhysicsBody of my sprites. I want to be informed when the fieldBitMask property changes so that I can take some action.

我覆盖了SKPhysicsBody，但是当我尝试将覆盖的类分配给像普通SKPhysicsBody对象这样的sprite节点时，出现了很多错误.我还考虑过为SKPhysicsBody进行扩展，但是Apple文档说:扩展可以为类型添加新功能，但不能覆盖现有功能."因此，似乎无法以这种方式覆盖fieldBitMask属性以使其成为属性观察器.

I overrode SKPhysicsBody but when I tried assigning the overridden class to a sprite node like a normal SKPhysicsBody object I got a bunch of errors. I also thought about making an extension for SKPhysicsBody, but Apple documentation says, "Extensions can add new functionality to a type, but they cannot override existing functionality." So it would seem that I can't override the fieldBitMask property this way to make it a property observer.

我知道如何在我创建的新的自定义类中创建属性观察器.但是，将属性观察器添加到Apple库中包含的类的现有属性中的最佳方法是什么?

I know how to create a property observer in a new custom class which I create. But what is the best way to add a property observer to an existing property in a class that is part of the Apple library?

推荐答案

我认为您可以使用实现 observeValue(forKeyPath:of:change:context:)方法.

I think you can use the Key Value Observing. You can add observer to a property changing.
You should implement observeValue(forKeyPath:of:change:context:) method in your observer class.

此处您可以找到Swift示例(键值观察"部分).

Here you can find Swift example ("Key-Value Observing" part).

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