NSUnknownKeyException : was sent to an object that is not KVC-compliant for the "player" property

Question

I have updated my code to swift 4 in Xcode 9. Before that it was working fine. But now AVplayer is crashing at observers below is the code where it is crashing.

addObserver(self, forKeyPath: "player.currentItem.duration", options: [.new, .initial], context: &playerViewControllerKVOContext)

And the log is

Terminating app due to uncaught exception 'NSUnknownKeyException',reason: '[ addObserver: forKeyPath:@"player.currentItem.duration" options:5 context:0x10ff74ac8] was sent to an object that is not KVC-compliant for the "player" property.'

Answer 1

Swift does not have the Key value observer of its own so for Swift 4 we have to add:

@objc dynamic

before the property whose value you need to observe. In your case it will be the AVPlayer instance. e.g.:

class MyPlayerCustomView: UIView {

@objc dynamic var myPlayer: AVPlayer?

}

Hope this solves your problem. It did solve mine!