iOS后臺保活按時間可分為短時保活和長時間保活
-
短時保活的方式
通過beginBackgroundTaskWithName來實現。在iOS7-iOS13可以申請到大約3分鐘的保活時間，在iOS 13以后只能申請30秒左右的時間。- 先通過監聽UIApplicationWillEnterForegroundNotification（應用進入前臺通知）和UIApplicationDidEnterBackgroundNotification（應用進入后臺通知）。
[[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 {}
- 使用Background Task在應用進入后臺時開啟保活，進入前臺時關閉保活。
@property (assign, nonatomic) UIBackgroundTaskIdentifier backgroundId;
- (void)appWillEnterForeground {
[self stopKeepAlive];
}
- (void)appDidEnterBackground {
_backgroundId = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
//申請的時間即將到時回調該方法
NSLog(@"BackgroundTask time gone");
[self stopKeepAlive];
}];
}
- (void)stopKeepAlive{
if (_backgroundId) {
[[UIApplication sharedApplication] endBackgroundTask:_backgroundId];
_backgroundId = UIBackgroundTaskInvalid;
}
}
如果想申請多一點時間，可以使用NSTimer循環申請保活時間，但是建議不要無限申請保活時間，因為系統如果發現該app一直在后臺運行，可能會直接殺掉app。
//開啟定時器 不斷向系統請求后臺任務執行的時間
NSTimer *_timer = [NSTimer scheduledTimerWithTimeInterval:5 target:self selector:@selector(applyForMoreTime) userInfo:nil repeats:YES];
[_timer fire];
//在這里我判斷了申請次數，加上第一次申請保活時間的次數一共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];
}
}
}
-
長時間保活
App長時間保活的方式有：播放無聲音樂、后臺持續定位、后臺下載資源、BGTaskScheduler等，這些需要在蘋果后臺開通后臺權限，并且在xcode中也開啟相關權限。
- 播放無聲音樂，適用于音樂類app。像騰訊視頻、愛奇藝等用了播放無聲音樂保活的方式。
在app進入后臺時開啟無聲音樂，進入前臺后停止無聲音樂。（更好的處理方式是先獲取短時保活，短時快過時再播放無聲音樂）示例如下：
監聽進入前后臺：
@property (nonatomic, strong) BackgroundPlayer* player;
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(appWillEnterForeground) name:UIApplicationWillEnterForegroundNotification object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(appDidEnterBackground) name:UIApplicationDidEnterBackgroundNotification object:nil];
- (void)appWillEnterForeground {
if (self.player) {
[self.player stopPlayBackgroundAlive];
}
}
- (void)appDidEnterBackground {
if (_player == nil) {
_player = [[BackgroundPlayer alloc] init];
}
[self.player startPlayer];
}
編寫音樂播放類：
#import <Foundation/Foundation.h>
#import <AVFoundation/AVFoundation.h>
@interface BackgroundPlayer : NSObject <AVAudioPlayerDelegate>
{
AVAudioPlayer* _player;
}
- (void)startPlayer;
- (void)stopPlayer;
@end
#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:@"你的音樂資源" 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
后臺持續定位
后臺下載資源
創建指定標識的后臺NSURLSessionConfiguration，配置好。
NSURL *url = [NSURL URLWithString:@"https://images.pexels.com/photos/3225517/pexels-photo-3225517.jpeg"];
NSURLSessionConfiguration *sessionConfig = [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:@"com.qishare.ios.wyw.backgroundDownloadTask"];
// 低于iOS13.0設備資源下載完后 可以得到通知 AppDelegate.m 文件中的 - (void)application:(UIApplication *)application handleEventsForBackgroundURLSession:(NSString *)identifier completionHandler:(void (^)(void))completionHandler
// iOS13.0+的設備資源下載完后 直接在下載結束的代理方法中會有回調
sessionConfig.sessionSendsLaunchEvents = YES;
// 當傳輸大數據量數據的時候，建議將此屬性設置為YES，這樣系統可以安排對設備而言最佳的傳輸時間。例如，系統可能會延遲傳輸大文件，直到設備連接充電器并通過Wi-Fi連接到網絡為止。 此屬性的默認值為NO。
sessionConfig.discretionary = YES;
NSURLSession *session = [NSURLSession sessionWithConfiguration:sessionConfig delegate:self delegateQueue:nil];
NSURLSessionDownloadTask *downloadTask = [session downloadTaskWithURL:url];
[downloadTask resume];
