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;

        }

    });

});

 
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