iOS 后台运行保活

前言

iOS有两种后台运行保活方式，第一种叫无声音乐保活（即在后台开启音频播放，只不过不需要播放出音量且不能影响其他音乐播发软件），第二种叫Background Task，但是这种方法在iOS 13以后只能申请短短的30秒钟时间，但是在iOS7-iOS13以前是可以申请到3分钟的保活时间的，当然我们也可以经过处理来申请到更多的保活时间。

无声音乐保活

---

(1)打开应用的Target页面Signing & Cabailities，添加Capability（Background Modes）勾选Audio，AirPlay，and Picture in Picture选项

(2)我们需要监听UIApplicationWillEnterForegroundNotification（应用进入前台通知）和UIApplicationDidEnterBackgroundNotification（应用进入后台通知）

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(appWillEnterForeground) name:UIApplicationWillEnterForegroundNotification object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(appDidEnterBackground) name:UIApplicationDidEnterBackgroundNotification object:nil];
- (void)appWillEnterForeground {}

- (void)appDidEnterBackground {}

(3)编写音乐播放类
BackgroundPlayer.h

#import 
#import 

@interface BackgroundPlayer : NSObject <AVAudioPlayerDelegate>
{
    AVAudioPlayer* _player;
}
- (void)startPlayer;

- (void)stopPlayer;
@end

BackgroundPlayer.m

#import "BackgroundPlayer.h"

@implementation BackgroundPlayer

- (void)startPlayer
{
    if (_player && [_player isPlaying]) {
        return;
    }
    AVAudioSession *session = [AVAudioSession sharedInstance];
    [[AVAudioSession sharedInstance] setMode:AVAudioSessionModeDefault error:nil];

    NSString* route = [[[[[AVAudioSession sharedInstance] currentRoute] outputs] objectAtIndex:0] portType];
    
    if ([route isEqualToString:AVAudioSessionPortHeadphones] || [route isEqualToString:AVAudioSessionPortBluetoothA2DP] || [route isEqualToString:AVAudioSessionPortBluetoothLE] || [route isEqualToString:AVAudioSessionPortBluetoothHFP]) {
        if (@available(iOS 10.0, *)) {
            [[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayAndRecord
                                             withOptions:(AVAudioSessionCategoryOptionMixWithOthers | AVAudioSessionCategoryOptionAllowBluetooth | AVAudioSessionCategoryOptionAllowBluetoothA2DP)
                                                   error:nil];
        } else {
            // Fallback on earlier versions
        }
    }else{
        [[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayAndRecord
                                         withOptions:(AVAudioSessionCategoryOptionMixWithOthers | AVAudioSessionCategoryOptionDefaultToSpeaker)
                                               error:nil];
    }
    
    [session setActive:YES error:nil];
    
    NSURL *url = [[NSBundle bundleWithPath:WECAST_CLOUD_BUNDLE_PATH]URLForResource:@"你的音乐资源" withExtension:nil];
    _player = [[AVAudioPlayer alloc] initWithContentsOfURL:url error:nil];
    [_player prepareToPlay];
    [_player setDelegate:self];
    _player.numberOfLoops = -1;
    BOOL ret = [_player play];
    if (!ret) {
        NSLog(@"play failed,please turn on audio background mode");
    }
}

- (void)stopPlayer
{
    if (_player) {
        [_player stop];
        _player = nil;
        AVAudioSession *session = [AVAudioSession sharedInstance];
        [session setActive:NO error:nil];
        NSLog(@"stop in play background success");
    }
}

@end

(4)在应用进入后台时开启保活

@property (nonatomic, strong) BackgroundPlayer* player;
- (void)appWillEnterForeground {
    if (self.player) {
        [self.player stopPlayBackgroundAlive];
    }
}

- (void)appDidEnterBackground {
    if (_player == nil) {
        _player = [[BackgroundPlayer alloc] init];
    }
    [self.player startPlayer];
}

Background Task保活

(1)同样我们需要监听UIApplicationWillEnterForegroundNotification（应用进入前台通知）和UIApplicationDidEnterBackgroundNotification（应用进入后台通知）

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(appWillEnterForeground) name:UIApplicationWillEnterForegroundNotification object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(appDidEnterBackground) name:UIApplicationDidEnterBackgroundNotification object:nil];
- (void)appWillEnterForeground {}

- (void)appDidEnterBackground {}

(2)使用Background Task申请保活时间，在应用进入后台时开启保活，在应用进入前台时关闭保活

@property (assign, nonatomic) UIBackgroundTaskIdentifier backgroundId;
- (void)appWillEnterForeground {
   [self stopKeepAlive];
}

- (void)appDidEnterBackground {
	_backgroundId = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
        //申请的时间即将到时回调该方法
        NSLog(@"BackgroundTask time gone");
        [self stopKeepAlive];
    }];
}

- (void)stopKeepAlive{
  if (_backgroundId) {
        [[UIApplication sharedApplication] endBackgroundTask:_backgroundId];
        _backgroundId = UIBackgroundTaskInvalid;
    }
}

(3)使用NSTimer循环申请保活时间，但是建议不要无限申请保活时间，因为系统如果发现该应用一直在后台运行时，是可能会直接crash掉你的应用的 ，错误码0x8badf00d

//开启定时器 不断向系统请求后台任务执行的时间
NSTimer *_timer = [NSTimer scheduledTimerWithTimeInterval:5 target:self selector:@selector(applyForMoreTime) userInfo:nil repeats:YES];
[_timer fire];

//在这里我判断了申请次数，加上第一次申请保活时间的次数一共6次。
@property(nonatomic,assign) int applyTimes;
-(void)applyForMoreTime {
    if ([UIApplication sharedApplication].backgroundTimeRemaining < 10) {
        _applyTimes += 1;
        NSLog(@"Try to apply for more time:%d",_applyTimes);
        [[UIApplication sharedApplication] endBackgroundTask:_backIden];
        _backIden = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
            [self stopKeepAlive];
        }];
        if(_applyTimes == 5){
            [_timer invalidate];
            _applyTimes = 0;
            [self stopKeepAlive];
        }
    }
}