UIScrollView setZoomScale：动画混乱scrollView纵横比

我正在开发一个带有UISCrollView视图的应用程序，里面是UIImageView。

I am developing an app with a view that holds a UISCrollView, inside which is a UIImageView.

当视图即将出现时，我执行setZoomScale操作：

When the view is about to appear, I perform a setZoomScale operation:

-(void) viewWillAppear:(BOOL)animated{
    [super viewWillAppear:animated];
    NSLog(@"bounds of current view");
    NSLog(@"widht: %f, height: %f", self.view.bounds.size.width,self.view.bounds.size.height);
    NSLog(@"size of the image");
    NSLog(@"widht: %f, height: %f", self.imageView.image.size.width,self.imageView.image.size.height);
    NSLog(@"size of the scrollView BEFORE resizing");
    NSLog(@"widht: %f, height: %f", self.scrollView.contentSize.width,self.scrollView.contentSize.height);
    [self.scrollView setZoomScale:0.5 animated:NO];
    NSLog(@"size of the scrollView AFTER resizing");
    NSLog(@"widht: %f, height: %f", self.scrollView.contentSize.width,self.scrollView.contentSize.height);
}

问题在于，如果图像是方形图像，则应用setZoomScale后scrollView不再是正方形。以下是运行上述代码的输出：

The problem is that if the image is a square one, after applying setZoomScale the scrollView is not square anymore. Here is the output of running the above code:

2012-01-16 21:41:01.678 WorldTour[22781:f803] bounds of current view
2012-01-16 21:41:01.680 WorldTour[22781:f803] widht: 320.000000, height: 367.000000
2012-01-16 21:41:01.681 WorldTour[22781:f803] size of the image
2012-01-16 21:41:01.682 WorldTour[22781:f803] widht: 612.000000, height: 612.000000
2012-01-16 21:41:01.683 WorldTour[22781:f803] size of the scrollView BEFORE resizing
2012-01-16 21:41:01.683 WorldTour[22781:f803] widht: 612.000000, height: 612.000000
2012-01-16 21:41:01.684 WorldTour[22781:f803] size of the scrollView AFTER resizing
2012-01-16 21:41:01.685 WorldTour[22781:f803] widht: 306.000000, height: 259.500000

因此，在运行代码后，612x612的方形scrollView变为306x259.5。
我缺少什么？出了什么问题？

So, after running the code, a square scrollView of 612x612 turns out to be 306x259.5. What am I missing? What is going wrong?

不应该[self.scrollView setZoomScale：0.5 animated：NO];转换高度和宽度的方式相同吗？

Shouldn't [self.scrollView setZoomScale:0.5 animated:NO]; transform height and width the same way?