延迟加载方法，可调用

-(void)setSlowlyClose{

    //下面设置延迟执行，否则太快看不到提示信息

    double delayInSeconds = 2.0;

    dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);

    dispatch_after(popTime, dispatch_get_main_queue(), ^(void){

        dispatch_async(dispatch_get_main_queue(), ^{

            NSArray *arr = self.navigationController.viewControllers;

            if (arr != nil && arr.count >= 3) {

                UIViewController *vc = [arr objectAtIndex:(arr.count-3)];

                [self.navigationController popToViewController:vc animated:YES];

            }

            else {

                [self.navigationController popViewControllerAnimated:TRUE];

            }

        });

    });

}