程序后台音频继续：

音频播放器后台播放 info.plist添加后台权限 注册音频后台模式到AVFoundation

示例代码

#import "AppDelegate.h"
#import <AVFoundation/AVFoundation.h>
@interface AppDelegate ()

@end

@implementation AppDelegate
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    // Override point for customization after application launch.
    
    // 1.获取音频会话
    AVAudioSession *session = [AVAudioSession sharedInstance];
    // 2.设置音频会话的类别为后台播放
    [session setCategory:AVAudioSessionCategoryPlayback error:nil];
    // 3.激活会话
    [session setActive:YES error:nil];

   return YES;
}

锁屏状态显示歌词

1、跟据三句歌词开启图片上下文生成图片

-(UIImage*)createImageWithPreviousLrc:(NSString*)previousLrc NextLrc:(NSString*)nextLrc CurrentLrc:(NSString*)currentLrc{
    UIImage *image = [UIImage imageNamed:[MusicTool playingMusic].icon];//获取当前播放歌曲的图片
    
    UIGraphicsBeginImageContext(image.size);//开启图片上下文
   
    [image drawInRect:CGRectMake(0, 0, image.size.width, image.size.height)];//绘制图片到上下文

    //前一句
    NSMutableParagraphStyle *style = [[NSMutableParagraphStyle alloc] init];
    style.alignment = NSTextAlignmentCenter;
    NSDictionary *attributes1 = @{NSFontAttributeName : [UIFont systemFontOfSize:14.0],
                                  NSForegroundColorAttributeName : [UIColor lightGrayColor],
                                  NSParagraphStyleAttributeName : style};
    CGRect previousRect = CGRectMake(0, image.size.height - 75, image.size.width, 25);
    [previousLrc drawInRect:previousRect withAttributes:attributes1];//绘制文字到上下文
    //下一句
    CGRect nextRect = CGRectMake(0, image.size.height - 25, image.size.width, 25);
    [nextLrc drawInRect:nextRect withAttributes:attributes1];//绘制文字到上下文
    //当前句
    NSDictionary *attributes2 = @{NSFontAttributeName : [UIFont systemFontOfSize:16.0],
                                  NSForegroundColorAttributeName : [UIColor whiteColor],
                                  NSParagraphStyleAttributeName : style};
    CGRect currentRect = CGRectMake(0, image.size.height - 50, image.size.width, 25);
    [currentLrc drawInRect:currentRect withAttributes:attributes2];//绘制文字到上下文
    
     return  UIGraphicsGetImageFromCurrentImageContext();//返回上下文的图片
}

2、将歌曲所有信息包装成字典

-(NSDictionary*)playingMusicDict:(UIImage*)lockImage{
    NSMutableDictionary *nowPayingInfo = [NSMutableDictionary dictionary];
    [nowPayingInfo setObject:[MusicTool playingMusic].name forKey:MPMediaItemPropertyAlbumTitle];
    [nowPayingInfo setObject:[MusicTool playingMusic].singer forKey:MPMediaItemPropertyArtist];
    MPMediaItemArtwork *artWork = [[MPMediaItemArtwork alloc] initWithImage:lockImage];
    [nowPayingInfo setObject:artWork forKey:MPMediaItemPropertyArtwork];
    [nowPayingInfo setObject:@(self.duration) forKey:MPMediaItemPropertyPlaybackDuration];
    [nowPayingInfo setObject:@(self.currentTime) forKey:MPNowPlayingInfoPropertyElapsedPlaybackTime];
    
    return nowPayingInfo;
}

3、将字典传递到锁屏界面

    //获取锁屏中心
    MPNowPlayingInfoCenter *playingInfoCenter = [MPNowPlayingInfoCenter defaultCenter];
    //设置播放的信息
    playingInfoCenter.nowPlayingInfo = [self playingMusicDict:lockImage];

4、 锁屏状态按钮响应

1、didFinishLaunchingWithOptions方法中添加锁屏响应允许
    [[UIApplication sharedApplication] beginReceivingRemoteControlEvents];
2、实现锁屏按钮事件（必须是在控制器）
- (void)remoteControlReceivedWithEvent:(UIEvent *)event
{
    switch (event.subtype) {

        case UIEventSubtypeRemoteControlPause:
            [self playOrPuase:nil];
            break;

        case UIEventSubtypeRemoteControlPreviousTrack:
            [self previous:nil];
            break;
            
        case UIEventSubtypeRemoteControlNextTrack:
            [self next:nil];
            break;
    }
}

5、拔掉耳机后自动暂停

1、注册音频输出改变通知
 [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(routeChange:) name:AVAudioSessionRouteChangeNotification object:nil];
2、判断输出类型
-(void)routeChange:(NSNotification *)notification{
    NSDictionary *dic=notification.userInfo;
    int changeReason= [dic[AVAudioSessionRouteChangeReasonKey] intValue];
    if (changeReason==AVAudioSessionRouteChangeReasonOldDeviceUnavailable) {
         // 判断输出改变的原因是因为旧输出已经不可用
        AVAudioSessionRouteDescription *routeDescription=dic[AVAudioSessionRouteChangePreviousRouteKey];
        AVAudioSessionPortDescription *portDescription= [routeDescription.outputs firstObject];
         // 判断原输出为耳机
        if ([portDescription.portType isEqualToString:@"Headphones"]) [self 暂停];
    }
}
3、控制器销毁时注销通知
-(void)dealloc{
    [[NSNotificationCenter defaultCenter] removeObserver:self name:AVAudioSessionRouteChangeNotification object:nil];
}