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.'

Thanks Tushar Sharma for the edit – Shuja Ud Din Sep 26 '17 at 07:45 — Shuja Ud Din, Sep 26 '17 at 07:45

score 22 · Accepted Answer · edited Mar 29 '20 at 08:15

22

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!

edited Mar 29 '20 at 08:15

pkamb

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answered Sep 26 '17 at 11:36

Junaid Mukhtar

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As an explanation, dynamic makes the property to be dispatched by the Objective-C runtime. That's why @objc is needed too. – javi_swift May 30 '19 at 10:53

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

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