后台播放音乐问题总结

后台保活一直是iOS开发中的一个难点问题,前面有一篇文章专门详细的分析了https://heron-newland.github.io/tutorial/2020/08/23/iOS保活方案研究/以及各种方案的优劣点,本文主要根据开发经验,介绍一种比较靠谱的方案.

关键点

1. 后台播放音乐一定需要申请后台任务, 即使app实现了后台常驻工功能.

/// 申请一段后台运行时间用于响铃激活
if ([UIApplication sharedApplication].applicationState == UIApplicationStateBackground) {
    if (self.backgroundTaskIdentifier == UIBackgroundTaskInvalid) {
        [self beginBackgroundTask];
    }
}

1. 申请后台任务是有时间限制的, 需要使用定时器去检测后台任务剩下的时间, 如果小于一定的值,那么需要重新去申请, 并且app在后台去申请后台任务会失败,最好在申请前播放一段无声音乐,然后去激活一下后台,然后再申请后台任务权限

-(void)checkBackgroundStatus{
if ([[UIApplication sharedApplication] backgroundTimeRemaining] < 61.0) {
    NSError *error;
    [[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayback withOptions:AVAudioSessionCategoryOptionMixWithOthers error:&error];
    if (error) {
        NSLog(@"重复申请后台失败%@",error);
    }
    [self ringTheBell:0 once:true volumeMax:false mute:true];
    [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:nil];
}
}

1. 后台音乐播放使用混合模式,这样能在其他音乐播放时,仍旧能播放后台音乐

1 2	NSError *error; [[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayback withOptions:AVAudioSessionCategoryOptionMixWithOthers error:&error];

1. 检测是否耳机连接

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//检测耳机是否连接,连接情况下音量最大只能调到30% -(BOOL)isHeadsetPluggedIn { AVAudioSessionRouteDescription* route = [[AVAudioSession sharedInstance] currentRoute]; for (AVAudioSessionPortDescription* desc in [route outputs]) { if ([[desc portType] isEqualToString:AVAudioSessionPortHeadphones] || [[desc portType] isEqualToString:AVAudioSessionPortBluetoothA2DP]){ return YES; }else{ return NO; } } return NO; }

完整的流程如下:

1. 让app常驻后台(申请后台蓝牙连接实现常驻)
2. 初始化一个定时器, 在app退到后台申请后台任务权限,并开启定时器
3. 定时器去检查后台任务的剩余时长, 如果小于61秒,那么播放一段无声音乐,重新申请后台任务权限
4. 执行后台任务(任意事件)
5. 回到前台结束后台任务, 结束定时器
6. 循环以上五个步骤

关键代码如下:

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- (id)init { self = [super init]; //初始化 [self audioSession]; //定时任务申请后台执行权限 self.timer = [NSTimer timerWithTimeInterval:3 repeats:true block:^(NSTimer * _Nonnull timer) { [self checkBackgroundStatus]; }]; [[NSRunLoop currentRunLoop] addTimer:self.timer forMode:NSRunLoopCommonModes]; [self.timer setFireDate:[NSDate distantFuture]]; return self; } //检测耳机是否连接,连接情况下音量最大只能调到30% - (BOOL)isHeadsetPluggedIn { AVAudioSessionRouteDescription* route = [[AVAudioSession sharedInstance] currentRoute]; for (AVAudioSessionPortDescription* desc in [route outputs]) { if ([[desc portType] isEqualToString:AVAudioSessionPortHeadphones] || [[desc portType] isEqualToString:AVAudioSessionPortBluetoothA2DP]){ return YES; }else{ return NO; } } return NO; } - (void)checkBackgroundStatus{ if ([[UIApplication sharedApplication] backgroundTimeRemaining] < 61.0) { NSError *error; [[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayback withOptions:AVAudioSessionCategoryOptionMixWithOthers error:&error]; if (error) { NSLog(@"重复申请后台失败%@",error); } [self doBackgroundTask]; [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:nil]; } } - (void)audioSessionInterrupt:(NSNotification *)noti { NSLog(@"收到系统级别的打断:%@",[noti userInfo]); int type = [noti.userInfo[AVAudioSessionInterruptionOptionKey] intValue]; switch (type) { case AVAudioSessionInterruptionTypeBegan: // 被打断 { NSLog(@"播放"); } break; case AVAudioSessionInterruptionTypeEnded: // 中断结束 { NSLog(@"暂停"); [self stopPlayer ]; } break; default: NSLog(@"其他"); break; } } //系统音量回调 - (void)volumeChangeNotification:(NSNotification *)noti { } - (void)audioPlayerDidFinishPlaying:(AVAudioPlayer *)player successfully:(BOOL)flag { [self restoreSystemVolume]; } - (void)stopPlayer { if (_player != nil) { NSError *err; [self.audioSession setActive:NO withOptions:AVAudioSessionSetActiveOptionNotifyOthersOnDeactivation error:&err]; NSLog(@"停止播放失败:%@",err); [_player stop]; _player = nil; [self restoreSystemVolume]; } } - (void)restoreSystemVolume { __weak typeof(self) weakSelf = self; dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.5 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{ if (weakSelf.originVolume > -1) { MPMusicPlayerController *mpVC = [MPMusicPlayerController applicationMusicPlayer]; mpVC.volume = weakSelf.originVolume; weakSelf.originVolume = -1; } }); } /// 后台任务 - (void)doBackgroundTask{ /// 申请一段后台运行时间用于响铃激活 if ([UIApplication sharedApplication].applicationState == UIApplicationStateBackground) { if (self.backgroundTaskIdentifier == UIBackgroundTaskInvalid) { [self beginBackgroundTask]; } } // dispatch_after(DISPATCH_TIME_NOW + 1, dispatch_get_main_queue(), ^{ NSError *err; MPMusicPlayerController *mpVC = [MPMusicPlayerController applicationMusicPlayer]; if (volumeMax) { // 正在播放，则不用重新保存系统音量值 if (_player == nil) { self.originVolume = mpVC.volume; } else { [self stopPlayer]; _player = nil; } #if DEBUG mpVC.volume = 0.3f; #else mpVC.volume = 1.0f; #endif } else { if (!shouldMute) {//设备断开 self.originVolume = mpVC.volume; mpVC.volume = 0.7f; }else{ self.originVolume = -1; } } if ([self isHeadsetPluggedIn]){ #if DEBUG mpVC.volume = 0.3f; #else mpVC.volume = 0.3f; #endif } NSURL *url = [[NSBundle mainBundle] URLForResource:[@(bellIndex) description] withExtension:@"caf"]; // 初始化播放器 _player = [[AVAudioPlayer alloc] initWithContentsOfURL:url error:&err]; NSLog(@"初始化播放器:%@",err); // 设置播放器声音 if (shouldMute) { _player.volume = 0.0f; }else{ _player.volume = 1.0f; } // 设置代理 _player.delegate = self; // 设置播放速率 _player.rate = 1.0; // 设置播放次数 负数代表无限循环 if (once) { _player.numberOfLoops = 1; } else { // 根据铃声时长定义，循环播放约15s NSArray *loops = @[@15, @5, @8, @45, @8, @8, @7, @15, @8, @15]; if (bellIndex < loops.count) { _player.numberOfLoops = [[loops objectAtIndex:bellIndex] integerValue]; } else { _player.numberOfLoops = 1; } } __weak typeof(self) weakSelf = self; dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)((once ? 0.1 : 0.6) * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{ [weakSelf.audioSession setCategory:AVAudioSessionCategoryPlayback error:nil]; [weakSelf.audioSession setActive:YES error:nil]; // 准备播放 if (![weakSelf.player prepareToPlay]) { NSLog(@"警报预播放失败"); } if (![weakSelf.player play]) { NSLog(@"警报播放失败"); } [[MPNowPlayingInfoCenter defaultCenter] setNowPlayingInfo:@{}]; }); // }); } // 申请后台 // https://www.jianshu.com/p/1f2572c08816 - (void)beginBackgroundTask { [self.timer setFireDate:[NSDate distantPast]]; NSLog(@"== beginBackgroundTask =="); __weak typeof(self) weakSelf = self; self.backgroundTaskIdentifier = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{ // 在时间到之前会进入这个block，一般是iOS7及以上是3分钟。按照规范，在这里要手动结束后台，你不写也是会结束的（据说会crash） NSLog(@"== backgroundTask expiration handler called =="); [weakSelf endBackgroundTask]; }]; } // 注销后台 - (void)endBackgroundTask { [self.timer setFireDate:[NSDate distantFuture]]; NSLog(@"== endBackgroundTask =="); if (self.backgroundTaskIdentifier != UIBackgroundTaskInvalid) { [[UIApplication sharedApplication] endBackgroundTask:self.backgroundTaskIdentifier]; self.backgroundTaskIdentifier = UIBackgroundTaskInvalid; } else { NSLog(@"== backgroundTaskIdentifier UIBackgroundTaskInvalid =="); } } // 继续播放后台背景音乐, 取消激活当前应用的audio session - (void)resumeBackgroundSoundWithError:(NSError **)error { [[AVAudioSession sharedInstance] setActive:NO withOptions:AVAudioSessionSetActiveOptionNotifyOthersOnDeactivation error:error]; } //暂停后台背景音乐的播放，激活当前应用的audio - (void)pauseBackgroundSoundWithError:(NSError **)error { AVAudioSession *session = [AVAudioSession sharedInstance]; [session setCategory:AVAudioSessionCategoryPlayback withOptions: AVAudioSessionCategoryOptionAllowBluetooth error:error]; [session setActive:YES error:error]; } - (void)pauseBackgroundSoundWithCategoryRecord { AVAudioSession *session = [AVAudioSession sharedInstance]; [session setCategory:AVAudioSessionCategoryRecord error:nil]; [session setActive:YES error:nil]; } - (void)audioPlayerDecodeErrorDidOccur:(AVAudioPlayer *)player error:(NSError *)error { NSLog(@"%@==%@",player,error); } - (AVAudioSession *)audioSession { if (!_audioSession) { _audioSession = [AVAudioSession sharedInstance]; NSError *error; [_audioSession setCategory:AVAudioSessionCategoryPlayback error:&error]; [_audioSession setActive:YES error:&error]; if (error) { NSLog(@"音频初始化失败:%@",error); } } return _audioSession; } @end