我无法在Swift iOS中使用NotificationCenter在控制台中获得任何输出

Question

我是Swift编程语言的新手，我想在歌曲改变时获得输出。代码没有任何错误。

下面是我的代码

import UIKit

导入MediaPlayer

类ViewController：UIViewController {

var trackChangedObserver : AnyObject?
override func viewDidLoad() {
    super.viewDidLoad()
    trackChangedObserver = NotificationCenter.default
        .addObserver(forName: .MPMusicPlayerControllerNowPlayingItemDidChange,
                     object: nil, queue: OperationQueue.main) { (notification) -> Void in
                        self.updateTrackInformation()
    }

}
deinit {
    NotificationCenter.default.removeObserver(trackChangedObserver!)
}

 func updateTrackInformation() {
    let musicPlayer = MPMusicPlayerController.systemMusicPlayer
    musicPlayer.beginGeneratingPlaybackNotifications()

    let currentTrack: MPMediaItem? = musicPlayer.nowPlayingItem
    let title = currentTrack?.value(forProperty: MPMediaItemPropertyTitle)
        as? String ?? "None"
    print(title)
    let artist = currentTrack?.value(forProperty: MPMediaItemPropertyArtist)
        as? String ?? "None"
    print(artist)
    let album = currentTrack?.value(forProperty: MPMediaItemPropertyAlbumTitle)
        as? String ?? "None"
    print(album)

}

}

Answer 1

您可以这样做：

let nc = NotificationCenter.default

nc.post（名称：.MPMusicPlayerControllerNowPlayingItemDidChange，对象：nil）

要注册以捕获正在发布的通知，请使用此：

nc.addObserver(self, selector: #selector(updateTrackInformation()), name: .MPMusicPlayerControllerNowPlayingItemDidChange, object: nil)

    @objc func updateTrackInformation(notification: NSNotification) {
    let musicPlayer = MPMusicPlayerController.systemMusicPlayer
    musicPlayer.beginGeneratingPlaybackNotifications()

    let currentTrack: MPMediaItem? = musicPlayer.nowPlayingItem
    let title = currentTrack?.value(forProperty: MPMediaItemPropertyTitle)
        as? String ?? "None"
    print(title)
    let artist = currentTrack?.value(forProperty: MPMediaItemPropertyArtist)
        as? String ?? "None"
    print(artist)
    let album = currentTrack?.value(forProperty: MPMediaItemPropertyAlbumTitle)
        as? String ?? "None"
    print(album)

}