Swift 5.1 NSInternalInconsistencyException 错误

Question

我正在更新旧的媒体播放器项目 (Swift 3) 并出现奇怪的错误：

由于未捕获的异常而终止应用程序 'NSInternalInconsistencyException'，原因：'不支持的操作方法 签名。必须返回 MPRemoteCommandHandlerStatus 或采取 完成处理程序作为第二个参数。

我在此代码上收到此错误：

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

 }

Swift 5.1 发生了什么变化？

Answer 1

根据文档，previousTrackCommand 选择器应将MPRemoteCommandEvent 作为第一个参数并返回MPRemoteCommandHandlerStatus：

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

所以你的handlePrevTrack 函数应该声明为：

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