Swift 5.1 NSInternalInconsistencyException error

Question

I am updating old media player project (Swift 3) and have weird error:

Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Unsupported action method signature. Must return MPRemoteCommandHandlerStatus or take a completion handler as the second argument.

I get this error on this code:

UIApplication.shared.beginReceivingRemoteControlEvents()
let commandCenter = MPRemoteCommandCenter.shared()
commandCenter.previousTrackCommand.addTarget(self, action: #selector(handlePrevTrack))

@objc func handlePrevTrack(){
        if playListEpisodes.count == 0 {
            return
        }

        let currentEpisodeIndex = playListEpisodes.firstIndex { (ep) -> Bool in
            return self.episode.title == ep.title && self.episode.author == ep.author
        }

        guard let index = currentEpisodeIndex else { return}
        let nextEpisode:Episode

        if index == 0 {
            nextEpisode = playListEpisodes[playListEpisodes.count - 1]
        }else {
            nextEpisode = playListEpisodes[index - 1]
        }

        self.episode = nextEpisode

 }

what changed in Swift 5.1?

Answer 1

According to documentation, previousTrackCommand selector should take MPRemoteCommandEvent as first argument and return MPRemoteCommandHandlerStatus:

func addTarget(handler: (MPRemoteCommandEvent) -> MPRemoteCommandHandlerStatus) -> Any

So your handlePrevTrack function should be declared as:

@objc func handlePrevTrack(_ event: MPRemoteCommandEvent) -> MPRemoteCommandHandlerStatus {
...
}