“隐藏"vs #keyPath(UIView.isHidden) [英] "hidden" vs #keyPath(UIView.isHidden)

问题描述

KVO 观察者不起作用，但 "hidden" 起作用.

KVO observer with #keyPath(UIView.isHidden) does not work, but "hidden" works.

很奇怪.是错误还是功能?

Very strange. Is it bug or feature?

child.addObserver(self, forKeyPath: "hidden", options: [.initial,.new], context: nil);

override func observeValue(forKeyPath keyPath: String?, of object: Any?, .change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
    if let view = object as? UIView, view.superview === self && keyPath == "hidden" {
        print("*");
    }
}

推荐答案

是错误还是功能?

Is it bug or feature?

假设这是一个已知的事实.重命名"意味着 Swift 假装 Objective-C Bool 属性的名称以 is... 开头，即使它不是.但是#keyPath机制在涉及到KVO和属性setter名称时并没有得到备忘录，并且property setter swizzling来实现KVO观察纯粹是一个Objective-C特性，所以你必须使用属性/setter 的真实名称，即Objective-C 名称，以便与Objective-C 进行通信以实现KVO 观察目的.

Let's say it's a known fact. "Renamification" means that Swift pretends that the name of an Objective-C Bool property starts with is... even when it doesn't. But the #keyPath mechanism didn't get the memo when it comes to KVO and property setter names, and property setter swizzling to implement KVO observing is purely an Objective-C feature, so you have to use the real name of the property / setter, i.e. the Objective-C name, so that communication with Objective-C works correctly for KVO observation purposes.

我已经提交了关于它的错误报告(https://bugs.swift.org/浏览/SR-2415)，理由是 Swift 可以在这方面表现得更聪明一点，但在 Swift 帮派回应之前，这只是您所知道和处理的事情.

I've filed a bug report on it (https://bugs.swift.org/browse/SR-2415) on the grounds that Swift could behave a little smarter about this, but until the Swift gang respond, it's just something you have know and deal with.

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