iOS- 使后台可以运行代码 比如定时器

//后台运行定时器

-(void)applicationDidEnterBackground:(UIApplication *)application{

UIApplication*   app = [UIApplication
sharedApplication];

__block 
UIBackgroundTaskIdentifier bgTask;

bgTask = [app beginBackgroundTaskWithExpirationHandler:^{

dispatch_async(dispatch_get_main_queue(), ^{

if (bgTask !=
UIBackgroundTaskInvalid)

{

bgTask = UIBackgroundTaskInvalid;

}

});

}];

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,
0), ^{

dispatch_async(dispatch_get_main_queue(), ^{

if (bgTask !=
UIBackgroundTaskInvalid)

{

bgTask = UIBackgroundTaskInvalid;

}

});

});

}