ios – 内容在使用UIScrollView缩小时跳转

我创建了一个简单的程序来滚动和缩放内容(UIImageView).它工作正常,但我尝试缩小时内容经常消失到右下角.但是因为我将minimumZoomScale设置为1.0f,它实际上没有缩小,只有内容跳出视图.更奇怪的是,在此之后我无法向上滚动.显然内容大小也很混乱.

我在示例代码中的设置如下图所示.

在(尝试)缩小后检查状态时,我发现了两个错误的东西.

> _scrollView.contentSize为480×360,不应小于1000×1000
> _scrollView.bounds以某种方式跳到顶部(即,_scrollView.bounds.origin.y始终为0)

为了处理上面的两个项目,我在uiscrollviewdelegate中添加了以下代码,现在它可以正常工作.

- (void)scrollViewWillBeginZooming:(UIScrollView *)scrollView withView:(UIView *)view
{
    if(scrollView == _scrollView && view == _contentView)
    {
        // Setting ivars for scrollViewDidZoom
        _contentOffsetBeforeZoom = _scrollView.contentOffset;
        _scrollViewBoundsBeforeZoom = _scrollView.bounds;
    }
}

- (void)scrollViewDidZoom:(UIScrollView *)scrollView
{
    if(scrollView == _scrollView)
    {
        // If you zoom out,there are cases where ScrollView content size becomes smaller than original,// even though minimum zoom scale = 1. In that case,it will mess with the contentOffset as well.
        if(_scrollView.contentSize.width < CONTENT_WIDTH || _scrollView.contentSize.height < CONTENT_HEIGHT)
        {
            _scrollView.contentSize = CGSizeMake(CONTENT_WIDTH,CONTENT_HEIGHT);
            _scrollView.contentOffset = _contentOffsetBeforeZoom;
        }

        // If you zoom out,there are cases where ScrollView bounds goes outsize of contentSize rectangle.
        if(_scrollView.bounds.origin.x + _scrollView.bounds.size.width > _scrollView.contentSize.width ||
           _scrollView.bounds.origin.y + _scrollView.bounds.size.height > _scrollView.contentSize.height)
        {
            _scrollView.bounds = _scrollViewBoundsBeforeZoom;
        }            
    }
}

但是,是否需要归结为此？这是一个非常简单的序列,很难相信Apple要求我们付出这样的努力.所以,我的赌注是我在这里遗漏了一些东西……

以下是我的原始代码.请帮我找到我做错了什么(或遗漏了什么)！

#define CONTENT_WIDTH 1000
#define CONTENT_HEIGHT 1000

  >>>> Snip >>>>

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view,typically from a nib.

    _scrollView = [[UIScrollView alloc] initWithFrame:CGRectMake(0,320,460)];
    _scrollView.contentSize = CGSizeMake(CONTENT_WIDTH,CONTENT_HEIGHT);
    _scrollView.backgroundColor = [UIColor blueColor];
    _scrollView.maximumZoomScale = 8.0f;
    _scrollView.minimumZoomScale = 1.0f;
    _scrollView.indicatorStyle = UIScrollViewIndicatorStyleWhite;
    _scrollView.scrollEnabled = YES;
    _scrollView.delegate = self;
    [self.view addSubview:_scrollView];

    _contentView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"sample.jpg"]]; // sample.jpg is 480x360
    CGPoint center = (CGPoint){_scrollView.contentSize.width / 2,_scrollView.contentSize.height / 2};
    _contentView.center = center;
    [_scrollView addSubview:_contentView];

    _scrollView.contentOffset = (CGPoint) {center.x - _scrollView.bounds.size.width / 2,center.y - _scrollView.bounds.size.height / 2};        
}

- (UIView *) viewForZoomingInScrollView:(UIScrollView *)scrollView
{
    if(scrollView == _scrollView)
    {
        return _contentView;
    }
    return nil;
}