是否可以观察Cocoa Touch中对象的readonly属性？ [英] Is it possible to observe a readonly property of an object in Cocoa Touch?

问题描述

我试图观察（readonly）一个UINavigationController的visibileViewController属性没有成功。我能够成功地观察一个readwrite属性，我为自己定义的测试目的在另一个类上。

I've attempted to observe the (readonly) visibileViewController property of a UINavigationController with no success. I was able to successfully observe a readwrite property I defined myself for testing purposes on another class.

是否可能观察者readonly属性？

Is it possible to observer readonly attributes?

推荐答案

是的，可以观察只读属性。但是，如果声明该属性的对象以不是键值观察符合 （例如，更改直接支持该属性的实例变量的值，而不会引起镇静 willChangeValueForKey：和 didChangeValueForKey：通知），则观察者不会自动通知KVO系统。如果你可以验证这个属性的值是否改变，并且你的观察者没有被通知，我会（1）在这里或其他地方发布一些代码，以便其他人可以帮助你找到你的错误和（2）如果没有错误您的代码，在Apple的雷达上提出错误。

Yes, it is possible to observe read-only properties. However, if the object that declares that property makes changes to the value of that property in a way that is not Key-Value Observing compliant (e.g. changes the value of the instance variable backing that property directly without seding willChangeValueForKey: and didChangeValueForKey: notifications) then observers will not automatically be notified by the KVO system. If you can verify that the value of this property is changing and your observers are not being notified, I would (1) post some code here or elsewhere so that others can help you find your bug and (2) if there is no bug in your code, file a bug on Apple's radar.

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