iOS_后台播放控制、锁屏封面

设置后台播放

设置App的plist，使app可以在后台播放音乐。
myApp-Info.plist中添加UIBackgroundModes键值，添加子键值为audio。
合适的位置添加代码

AVAudioSession  *session  =  [AVAudioSession  sharedInstance];
[session setActive:YES error:nil];
[session setCategory:AVAudioSessionCategoryPlayback error:nil];

添加播放控制器（Remote Control Events）

//1. 告诉系统，我们要接受远程控制事件
-  (BOOL)application:(UIApplication  *)application didFinishLaunchingWithOptions:(NSDictionary  *)launchOptions {
    //....
    [[UIApplication sharedApplication] beginReceivingRemoteControlEvents];
    [self becomeFirstResponder];
}

//2. 可以成为第一响应者
- (BOOL)canBecomeFirstResponder {
    return  YES;
}

//3. 响应远程音乐播放控制消息
 - (void)remoteControlReceivedWithEvent:(UIEvent *)event{
        switch (event.subtype) {
           case UIEventSubtypeRemoteControlPlay:
               nslog(@"play");
           break;
           case UIEventSubtypeRemoteControlPause:
               nslog(@"pause");
           break;
           case UIEventSubtypeRemoteControlNextTrack:
               nslog(@"next");
               break;
           case UIEventSubtypeRemoteControlPreviousTrack:
              nslog(@"previous");;
              break;          
           default:
              break;
       }
 }
    // available in iPhone OS 3.0 
    UIEventSubtypeNone                              = 0,
    
    // for UIEventTypeMotion, available in iPhone OS 3.0  
    UIEventSubtypeMotionShake                       = 1,
     
    //这之后的是我们需要关注的枚举信息
    // for UIEventTypeRemoteControl, available in iOS 4.0
    //点击播放按钮或者耳机线控中间那个按钮
    UIEventSubtypeRemoteControlPlay                 = 100,
    
    //点击暂停按钮
    UIEventSubtypeRemoteControlPause                = 101,
    
    //点击停止按钮
    UIEventSubtypeRemoteControlStop                 = 102,
    
    //点击播放与暂停开关按钮(iphone抽屉中使用这个)
    UIEventSubtypeRemoteControlTogglePlayPause      = 103,
        
    //点击下一曲按钮或者耳机中间按钮两下
    UIEventSubtypeRemoteControlNextTrack            = 104,
    
    //点击上一曲按钮或者耳机中间按钮三下   
    UIEventSubtypeRemoteControlPreviousTrack        = 105,
    
    //快退开始 点击耳机中间按钮三下不放开
    UIEventSubtypeRemoteControlBeginSeekingBackward = 106,
    
    //快退结束 耳机快退控制松开后
    UIEventSubtypeRemoteControlEndSeekingBackward   = 107,
    
    //开始快进 耳机中间按钮两下不放开
    UIEventSubtypeRemoteControlBeginSeekingForward  = 108,
    
    //快进结束 耳机快进操作松开后
    UIEventSubtypeRemoteControlEndSeekingForward    = 109,

设置后台信息显示及锁屏界面设置

 #import <MediaPlayer/MediaPlayer.h>
 - (void)setLockingInfo {
   NSMutableDictionary *dict = [[NSMutableDictionary alloc] init];
   //设置歌曲题目
   [dict setObject:@"题目" forKey:MPMediaItemPropertyTitle];
   //设置歌手名
   [dict setObject:@"歌手" forKey:MPMediaItemPropertyArtist];
   //设置专辑名
   [dict setObject:@"专辑" forKey:MPMediaItemPropertyAlbumTitle];
   //设置显示的图片
   UIImage *newImage = [UIImage imageNamed:@"43.png"];
   [dict setObject:[[MPMediaItemArtwork alloc] initWithImage:newImage] forKey:MPMediaItemPropertyArtwork];
  //设置歌曲时长
  [dict setObject:[NSNumber numberWithDouble:300] forKey:MPMediaItemPropertyPlaybackDuration];
  //设置已经播放时长
  [dict setObject:[NSNumber numberWithDouble:150] forKey:MPNowPlayingInfoPropertyElapsedPlaybackTime]; 
  //更新字典
  [[MPNowPlayingInfoCenter defaultCenter] setNowPlayingInfo:dict];
}