请求更多的后台时间

- (void)applicationDidEnterBackgtound
{
    UIApplication *app = [UIApplication sharedApplication];
    __block UIBackgroundTaskIdentifier taskId;
    
    taskId = [app beginBackgroundTaskWithExpirationHandler:^{
        NSLog(@"%@",NSStringFromSelector(_cmd));
        [app endBackgroundTask:taskId];
    }];
    
    if (taskId == UIBackgroundTaskInvalid) {
        return;
    }
    
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        //做一些额外的操作
        [app endBackgroundTask:taskId];
    });
}