iOS 10 - NSKeyValueObservation 在 deinit 时崩溃

Question

我正在使用 NSKeyValueObservation 观察 WKWebView 的子类中的属性。

它在 iOS 11 上运行良好，但在 iOS 10 上的 deinit 上崩溃。

在控制台上打印错误日志

*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'An instance 0x15209e600 of class Rakuemon.WebView was deallocated while key value observers were still registered with it. Current observation info: <NSKeyValueObservationInfo 0x170232da0> (
<NSKeyValueObservance 0x170259bf0: Observer: 0x17027d500, Key path: loading, Options: <New: NO, Old: NO, Prior: NO> Context: 0x0, Property: 0x170643ba0>
<NSKeyValueObservance 0x170643480: Observer: 0x170c72f80, Key path: estimatedProgress, Options: <New: YES, Old: NO, Prior: NO> Context: 0x0, Property: 0x170643330>
<NSKeyValueObservance 0x170642c70: Observer: 0x17086c0c0, Key path: title, Options: <New: YES, Old: NO, Prior: NO> Context: 0x0, Property: 0x1706437b0>
)'

代码

class WebView: WKWebView {

    // MARK: - Properties

    weak var delegate: WebViewDelegate?

    // MARK: - Private properties

    private var contentSizeObserver: NSKeyValueObservation?
    private var loadingObserver: NSKeyValueObservation?
    private var estimatedProgressObserver: NSKeyValueObservation?
    private var titleObserver: NSKeyValueObservation?

    // MARK: - Life cycle

    override init(frame: CGRect, configuration: WKWebViewConfiguration) {
        super.init(frame: frame, configuration: configuration)
        setupObserver()
    }

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

// MARK: - Private functions

private extension WebView {
    func setupObserver() {
        contentSizeObserver = scrollView.observe(\.contentSize, options: [.old, .new], changeHandler: { [unowned self] _, change in
            guard let oldSize = change.oldValue, let newSize = change.newValue, oldSize != newSize else { return }
            self.delegate?.webView?(self, didChangeSizeFrom: oldSize, to: newSize)
        })

        loadingObserver = observe(\.isLoading, changeHandler: { [unowned self] _, _ in
            self.delegate?.webViewIsLoading?(self)
        })

        estimatedProgressObserver = observe(\.estimatedProgress, options: [.new], changeHandler: { [unowned self] _, change in
            guard let newValue = change.newValue else { return }
            self.delegate?.webView?(self, didChangeEstimatedProgress: newValue)
        })

        titleObserver = observe(\.title, options: [.new], changeHandler: { [unowned self] _, change in
            guard let title = change.newValue else { return }
            self.delegate?.webView?(self, didChangeTitle: title ?? "")
        })
    }
}

问题

我还发现 contentSizeObserver，它观察到 scrollView.contentSize，而不是 self 的属性，没有导致崩溃。

那么，观察 self 在 iOS 10 到 NSKeyValueObservation 上的属性的正确方法是什么？或取消注册？

Answer 1

看起来像苹果虫 – https://bugs.swift.org/browse/SR-5816

This is happening because NSKeyValueObservation holds a weak reference to an object. That weak reference turns to nil too soon.

在某些情况下，可以通过使用生命周期方法（viewDidDissapear 等）找到解决方法。在其他情况下，您应该使用旧的 obj-c api (addObserver / removeObserver / observeValue) 来支持 iOS 10.

Answer 2

更新于 2019/10/16

这似乎仍然发生在 iOS 10.3 和 Xcode 11 和 Swift 5.1 上，我创建了一个 sample project to test it by using code from SR-5752。

到目前为止我想出的最简单的方法是这样的：

// Environment: Xcode 11.1, Swift 5.1, iOS 10.3
deinit {
    if #available(iOS 11.0, *) {} else if let observer = observer {
        removeObserver(observer, forKeyPath: "foo")
    }
}

可以注意到我只在 iOS 10 和更低版本上调用 removeObserver(_:forKeyPath) 因为作为 Stacy Smith ，在 iOS 13 上崩溃（可以在示例中轻松重现项目）。

我也试过 Bryan Rodríguez's ，但没有成功。也许我错过了什么？

// Environment: Xcode 11.1, Swift 5.1, iOS 10.3
deinit {
    // Also tried only either one, no luck
    self.observer?.invalidate() 
    self.observer = nil
}

Answer 3

这对我有用：

deinit {
    titleObserver = nil
}

iOS 10 - NSKeyValueObservation 在 deinit 时崩溃

iOS 10 - NSKeyValueObservation crash on deinit

key-value-observing

swift

ios10

swift4

在控制台上打印错误日志

代码

问题