Crash on deinit UIView was deallocated while key value observers were still registered with it

[NickSuglobov]

I have a crash:

Fatal Exception: NSInternalInconsistencyException
An instance 0x151eabd0 of class UIView was deallocated while key value observers were still registered with it. Current observation info: <NSKeyValueObservationInfo 0x151b6c10> ( <NSKeyValueObservance 0x14384cd0: Observer: 0x151b0090, Key path: hidden, Options: <New: YES, Old: YES, Prior: NO> Context: 0x151b0180, Property: 0x8814fc0> )

In my view I have this code:

deinit {
    stackView.arrangedSubviews.forEach { view in
      stackView.removeArrangedSubview(view)
    }
  }

After investigation I found that method removeArrangedSubview does not call removeHiddenListener. Why?

You are removing listeners by code:

deinit {
        // This removes `hidden` value KVO observers using didSet()
        { self.arrangedSubviews = [] }()
    }

But arrangedSubviews are already empty. Why don't you remove listeners for all listeners in registeredKvoSubviews array?