ScrollView中的UIImageView纵横比不起作用

我在故事板中定义了UIScrollView，带有插座 . 此scrollview通过代码（不在故事板上）添加了一个UIImageView . 当我运行应用程序时，图像被拉伸出方面 . 只要我触摸缩放图像，它就会捕捉到适当的宽高比 .

这里发生了什么？！

@IBOutlet var scrollView: UIScrollView!

var imageView = UIImageView()
var selectedImage: UIImage!

override func viewDidLoad() {
    super.viewDidLoad()

    scrollView.delegate = self
    imageView.frame = CGRectMake(0, 0, scrollView.frame.size.width, scrollView.frame.size.height)
    imageView.image = selectedImage
    imageView.contentMode = .ScaleAspectFit
    imageView.userInteractionEnabled = true


    scrollView.contentMode = .ScaleAspectFit
    scrollView.addSubview(imageView)

    let scrollViewFrame = scrollView.frame
    let scaleWidth = scrollViewFrame.size.width / scrollView.contentSize.width
    let scaleHeight = scrollViewFrame.size.height / scrollView.contentSize.height
    let minScale = min(scaleHeight, scaleWidth)
    scrollView.minimumZoomScale = 0.3
    scrollView.maximumZoomScale = 1
    scrollView.zoomScale = minScale

    centerScrollViewContents()


    self.closeBtn.layer.cornerRadius = CGRectGetWidth(self.closeBtn.frame)/20.0


}

加载时：

完全移动变焦后：

ALMOST FIXED: 我编辑了代码来定义viewWillLayoutSubviews中的imageView.frame而不是viewDidLoad，如下面的答案所示 . 我现在有一个新问题 - 图像无法放大...它允许您缩放，直到您松开手指然后它快速恢复到原始大小 .

这与scrollView.maximumZoomScale不够大吗？

corrected code:

override func viewWillLayoutSubviews() {
    super.viewWillLayoutSubviews()
    imageView.frame = CGRectMake(0, 0, scrollView.frame.size.width, scrollView.frame.size.height)
}
override func viewDidLoad() {
    super.viewDidLoad()

    scrollView.delegate = self
    //imageView.frame = CGRectMake(0, 0, scrollView.frame.size.width, scrollView.frame.size.height)
    imageView.image = selectedImage
    imageView.contentMode = .ScaleAspectFit
    imageView.userInteractionEnabled = true


    scrollView.contentMode = .ScaleAspectFit
    scrollView.addSubview(imageView)

    let scrollViewFrame = scrollView.frame
    let scaleWidth = scrollViewFrame.size.width / scrollView.contentSize.width
    let scaleHeight = scrollViewFrame.size.height / scrollView.contentSize.height
    let minScale = min(scaleHeight, scaleWidth)
    scrollView.minimumZoomScale = 0.3
    scrollView.maximumZoomScale = 2.0
    scrollView.zoomScale = minScale

    centerScrollViewContents()


    self.closeBtn.layer.cornerRadius = CGRectGetWidth(self.closeBtn.frame)/20.0


}