CATransition *animation = [[CATransition alloc]init];    animation.type = kCATransitionFromTop;    animation.subtype = kCATransitionFromTop; //向上滚动，其他方向自己设置    animation.duration = 0.3;    [self.imageView.layer addAnimation:animation forKey:nil];    NSString *imageName = [NSString stringWithFormat:@"ad%ld.jpg",++currentIndex % 5 + 1];    UIImage *image = [UIImage imageNamed:imageName];    self.imageView.image = image;