12.使APP长期后台运行

- (void)applicationDidEnterBackground:(UIApplication *)application {
    [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:nil];
    [self backTask];
}

-(void)backTask
{
    if ([[UIApplication sharedApplication] backgroundTimeRemaining] < 61.0) {
        [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:nil];
    }
}