Swift - 使用AVPlayer制作一个音乐播放器2（后台播放、操作、图片显示）

在前文中，我介绍了如何使用  AVFoundation 框架来制作一个简单的音频播放器（ 点击查看）。但这个播放器不支持后台播放，程序退到后台时音乐就会停止播放。

本文接着介绍如何实现后台播放功能。

1，效果图

（1）运行程序并播放音乐。这时我们返回桌面或者关闭屏幕，会发现音乐仍然在播放。

（2）在锁屏界面上，会显示当前的歌曲信息、专辑图片、当前进度等。同时还提供相关的控制按钮供我们使用。

（3）同样的，在上拉的音乐控制面板中，也会显示相关信息，并允许我们进行相关操作。

               

2，实现步骤

（1）为了让播放器能在后台持续播放，我们需要将  Targets ->  Capabilities -> BackgroundModes 设为  ON，同时勾选“ Audio, AirPlay, and Picture in Picture”。

（2）同时还要在  AppDelegate.swift 中注册后台播放。

import  UIKit
import  AVFoundation

@UIApplicationMain
class  AppDelegate :  UIResponder ,  UIApplicationDelegate  {

    var  window:  UIWindow ?


    func  application(_ application:  UIApplication , didFinishLaunchingWithOptions
        launchOptions: [ UIApplicationLaunchOptionsKey :  Any ]?) ->  Bool  {

        // 注册后台播放
        let  session =  AVAudioSession .sharedInstance()
        do {
            try session.setActive( true )
            try session.setCategory( AVAudioSessionCategoryPlayback )
        } catch {
            print (error)
        }

        return  true
    }

    func  applicationWillResignActive(_ application:  UIApplication ) {
    }

    func  applicationDidEnterBackground(_ application:  UIApplication ) {
    }

    func  applicationWillEnterForeground(_ application:  UIApplication ) {
    }

    func  applicationDidBecomeActive(_ application:  UIApplication ) {
    }

    func  applicationWillTerminate(_ application:  UIApplication ) {
    }
}

（3） ViewController.swift（主视图代码，黄色部分为新增的代码）

import  UIKit
import  AVFoundation
import  MediaPlayer

class  ViewController :  UIViewController  {

    //播放按钮
    @IBOutlet  weak  var  playButton:  UIButton !

    //可拖动的进度条
    @IBOutlet  weak  var  playbackSlider:  UISlider !

    //当前播放时间标签
    @IBOutlet  weak  var  playTime:  UILabel !

    //播放器相关
    var  playerItem: AVPlayerItem ?
    var  player: AVPlayer ?

    override  func  viewDidLoad() {
        super .viewDidLoad()

        //初始化播放器
        let  url =  URL (string:  "http://mxd.766.com/sdo/music/data/3/m10.mp3" )
        playerItem =  AVPlayerItem (url: url!)
        player =  AVPlayer (playerItem: playerItem!)

        //设置进度条相关属性
        let  duration :  CMTime  = playerItem!.asset.duration
        let  seconds :  Float64  =  CMTimeGetSeconds (duration)
        playbackSlider!.minimumValue = 0
        playbackSlider!.maximumValue =  Float (seconds)
        playbackSlider!.isContinuous =  false

        //播放过程中动态改变进度条值和时间标签
        player!.addPeriodicTimeObserver(forInterval:  CMTimeMakeWithSeconds (1, 1),
                                        queue:  DispatchQueue .main) { ( CMTime ) ->  Void  in
            if  self .player!.currentItem?.status == .readyToPlay &&  self .player?.rate != 0{
                //更新进度条进度值
                let  currentTime =  CMTimeGetSeconds ( self .player!.currentTime())
                self .playbackSlider!.value =  Float (currentTime)

                //一个小算法，来实现00：00这种格式的播放时间
                let  all: Int = Int (currentTime)
                let  m: Int =all % 60
                let  f: Int = Int (all/60)
                var  time: String = ""
                if  f<10{
                    time= "0\(f):"
                } else  {
                    time= "\(f)"
                }
                if  m<10{
                    time+= "0\(m)"
                } else  {
                    time+= "\(m)"
                }
                //更新播放时间
                self .playTime!.text=time

                //设置后台播放显示信息
                self .setInfoCenterCredentials(playbackState: 1)
            }
        }
    }

    //播放按钮点击
    @IBAction  func  playButtonTapped(_ sender:  Any ) {
        //根据rate属性判断当天是否在播放
        if  player?.rate == 0 {
            player!.play()
            playButton.setTitle( "暂停" ,  for : .normal)
        }  else  {
            player!.pause()
            playButton.setTitle( "播放" ,  for : .normal)
            //后台播放显示信息进度停止
            setInfoCenterCredentials(playbackState: 0)
        }
    }

    //拖动进度条改变值时触发
    @IBAction  func  playbackSliderValueChanged(_ sender:  Any ) {
        let  seconds :  Int64  =  Int64 (playbackSlider.value)
        let  targetTime: CMTime  =  CMTimeMake (seconds, 1)
        //播放器定位到对应的位置
        player!.seek(to: targetTime)
        //如果当前时暂停状态，则自动播放
        if  player!.rate == 0
        {
            player?.play()
            playButton.setTitle( "暂停" ,  for : .normal)
        }
    }

    //页面显示时添加相关通知监听
    override  func  viewWillAppear(_ animated:  Bool ) {
        //播放完毕
        NotificationCenter . default .addObserver( self , selector: #selector(finishedPlaying),
            name:  NSNotification . Name . AVPlayerItemDidPlayToEndTime , object: playerItem)

        //告诉系统接受远程响应事件，并注册成为第一响应者
        UIApplication .shared.beginReceivingRemoteControlEvents()
        self .becomeFirstResponder()
    }

    //页面消失时取消歌曲播放结束通知监听
    override  func  viewWillDisappear(_ animated:  Bool ) {
        NotificationCenter . default .removeObserver( self )

        //停止接受远程响应事件
        UIApplication .shared.endReceivingRemoteControlEvents()
        self .resignFirstResponder()
    }

    //歌曲播放完毕
    func  finishedPlaying(myNotification: NSNotification ) {
        print ( "播放完毕!" )
        let  stopedPlayerItem:  AVPlayerItem  = myNotification.object  as !  AVPlayerItem
        stopedPlayerItem.seek(to: kCMTimeZero)
    }

    //是否能成为第一响应对象
    override  var  canBecomeFirstResponder:  Bool  {
        return  true
    }

    // 设置后台播放显示信息
    func  setInfoCenterCredentials(playbackState:  Int ) {
        let  mpic =  MPNowPlayingInfoCenter . default ()

        //专辑封面
        let  mySize =  CGSize (width: 400, height: 400)
        let  albumArt =  MPMediaItemArtwork (boundsSize:mySize) { sz  in
            return  UIImage (named:  "cover" )!
        }

        //获取进度
        let  postion =  Double ( self .playbackSlider!.value)
        let  duration =  Double ( self .playbackSlider!.maximumValue)

        mpic.nowPlayingInfo = [ MPMediaItemPropertyTitle :  "我是歌曲标题" ,
                               MPMediaItemPropertyArtist :  "hangge.com" ,
                               MPMediaItemPropertyArtwork : albumArt,
                               MPNowPlayingInfoPropertyElapsedPlaybackTime : postion,
                               MPMediaItemPropertyPlaybackDuration : duration,
                               MPNowPlayingInfoPropertyPlaybackRate : playbackState]
    }

    //后台操作
    override  func  remoteControlReceived(with event:  UIEvent ?) {
        guard  let  event = event  else  {
            print ( "no event\n" )
            return
        }

        if  event.type ==  UIEventType .remoteControl {
            switch  event.subtype {
            case  .remoteControlTogglePlayPause:
                print ( "暂停/播放" )
            case  .remoteControlPreviousTrack:
                print ( "上一首" )
            case  .remoteControlNextTrack:
                print ( "下一首" )
            case  .remoteControlPlay:
                print ( "播放" )
                player!.play()
            case  .remoteControlPause:
                print ( "暂停" )
                player!.pause()
                //后台播放显示信息进度停止
                setInfoCenterCredentials(playbackState: 0)
            default :
                break
            }
        }
    }

    override  func  didReceiveMemoryWarning() {
        super .didReceiveMemoryWarning()
    }
}

源码下载： hangge_1668.zip

原文出自： www.hangge.com   转载请保留原文链接： http://www.hangge.com/blog/cache/detail_1669.html