为什么我可以支持缩放uiScrollView而不符合uiScrollViewDelegate?

为了支持在uiScrollView中缩放图像,我认为我必须使myController符合uiScrollView委托,如下所示。但它在不符合uiscrollViewDelegate的情况下工作正常,即使编译器生成以下警告消息。
警告:类“MyController”未实现“UIScrollViewDelegate”协议

是否必须符合头文件中的uiscrollViewDelegate?
如果我忘了遵守,有什么副作用吗?

//@interface MyController : UIViewController <UIScrollViewDelegate>
@interface MyController : UIViewController
{
    UIScrollView *scrollView;
    UIImageView *imageView;
}
@end

@implementation HelloController
- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView
{
    return imageView;
}

- (void)loadView
{
    UIImage *img = [UIImage imageNamed:@"foo.png"];
    imageView = [[UIImageView alloc] initWithImage:img];
    imageView.userInteractionEnabled = NO;

    scrollView = [[UIScrollView alloc] initWithFrame: [[UIScreen mainScreen] applicationFrame]];
    [scrollView setScrollEnabled:YES];
    [scrollView setContentSize:[imageView size]];
    [scrollView setMaximumZoomScale:2.0f];
    [scrollView setMinimumZoomScale:0.5f];
    [scrollView setDelegate:self];

    [scrollView addSubview:imageView];

    self.view = scrollView;
    [scrollView release];
}
@end