Question

我正在关注可以平移和缩放图片的UIScrollView上的Raywenderlich教程（https://www.raywenderlich.com/159481/uiscrollview-tutorial-getting-started）。除了我以编程方式创建视图和布局约束之外，我的代码与他们的代码完全相同。我没有工作。

我发现问题是ImageView在bounds中的viewDidLayoutSubviews()值为零{}。但是，我是否在Storyboard或代码中创建了约束，这不是什么区别，对吧？如果是这样，任何建议的解决方法将不胜感激。 viewDidLoad()中的部分是我自己的代码。

class ComposeController: UIViewController {

    let scrollView = UIScrollView()
    let imageView = UIImageView()
    var imageViewBottomConstraint: NSLayoutConstraint!
    var imageViewLeadingConstraint: NSLayoutConstraint!
    var imageViewTopConstraint: NSLayoutConstraint!
    var imageViewTrailingConstraint: NSLayoutConstraint!

    override func viewDidLoad() {
        super.viewDidLoad()

        imageView.image = MyImage //from Assets
        scrollView.delegate = self       
        view.addSubview(scrollView)
        scrollView.addSubview(imageView)

        scrollView.translatesAutoresizingMaskIntoConstraints = false
        scrollView.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
        scrollView.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
        scrollView.leftAnchor.constraint(equalTo: view.leftAnchor).isActive = true
        scrollView.rightAnchor.constraint(equalTo: view.rightAnchor).isActive = true

        imageView.translatesAutoresizingMaskIntoConstraints = false
        imageViewTopConstraint = imageView.topAnchor.constraint(equalTo: scrollView.topAnchor)
        imageViewBottomConstraint = imageView.bottomAnchor.constraint(equalTo: scrollView.bottomAnchor)
        imageViewLeadingConstraint = imageView.leftAnchor.constraint(equalTo: scrollView.leftAnchor)
        imageViewTrailingConstraint = imageView.rightAnchor.constraint(equalTo: scrollView.rightAnchor)
        imageViewTopConstraint.isActive = true
        imageViewBottomConstraint.isActive = true
        imageViewLeadingConstraint.isActive = true
        imageViewTrailingConstraint.isActive = true

    }

    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()
        updateMinZoomScaleForSize(view.bounds.size)
    }

    fileprivate func updateMinZoomScaleForSize(_ size: CGSize) {
        let widthScale = size.width / imageView.bounds.width
        let heightScale = size.height / imageView.bounds.height
        let minScale = min(widthScale, heightScale)

        scrollView.minimumZoomScale = minScale
        scrollView.zoomScale = minScale
    }
}

extension ComposeController: UIScrollViewDelegate {
    func viewForZooming(in scrollView: UIScrollView) -> UIView? {
        return imageView
    }
}

Answer 1

根据Apple的viewDidLayoutSubviews()文档：

当视图控制器视图的边界发生变化时，视图会调整其子视图的位置，然后系统会调用此方法。但是，调用此方法并不表示已调整视图子视图的各个布局。每个子视图都负责调整自己的布局。

您可以通过调用以下方式获取视图以布置各个子视图：

self.view.setNeedsLayout()
self.view.layoutIfNeeded()

ViewDidLayoutSubviews（）中ImageView的边界为零

1 个答案: