UIButton状态的键值观察 [英] Key-value observing on UIButton's State

问题描述

UIButton有一个州财产，所有帐户似乎都符合KVO标准，没有其他说明文件。但是，当我向UIButton的state属性添加一个观察者时，从未调用过观察者回调。怎么来？

UIButton has a state property, which appears to be KVO compliant by all accounts and there is no documentation to indicate otherwise. However, when I added an observer to a UIButton's state property, the observer callback was never invoked. How come?

推荐答案

如果查看UIControl的文档，则会将state属性标记为：来自其他旗帜。

If you look at the documentation of UIControl, the state property is marked: synthesized from other flags.

我想这就是为什么这个属性的更改不符合KVO。

I guess this is why changes to this property are not KVO compliant.

但是，您只需注册和观察您需要的值 - 突出显示，选中，启用。这些属性符合KVO，您将获得观察者回调当他们改变时。

However, you can simply register and observer for the values you need - highlighted, selected, enabled. These properties are KVO compliant and you will get the observer callback when they change.

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