带有错误的UIView，在编程上，UIScrollView的可滚动内容大小不明确。只有第一次

Question

我的UIViewController包含一个UIScrollView，正在遇到奇怪的行为。ViewController是从另一个ViewController推送的。该视图的布局如下

• UIView
  • UIScrollView
    • UIView
      • UIImageVIew
        • UILabel
      • UIStackView

我设置约束和更新stackView内容的方式如下。

private extension PresentationViewController {

    func setupView() {
        isScrolling = true

        view.addSubview(scrollView)
        scrollView.snp.makeConstraints { (builder) in
            builder.top.left.bottom.right.equalToSuperview()
        }

        scrollView.addSubview(contenView)
        contenView.snp.makeConstraints { (builder) in
            builder.top.left.bottom.right.equalToSuperview()
            builder.width.equalToSuperview()
        }

        contenView.addSubview(headerImageView)
        headerImageView.snp.makeConstraints { (builder) in
            builder.top.left.right.equalToSuperview()
            builder.height.equalTo(view.frame.height / 2)
        }

        headerImageView.addSubview(headerTitleLabel)
        headerTitleLabel.snp.makeConstraints { (builder) in
            builder.left.right.equalToSuperview()
            builder.centerX.equalToSuperview()
            builder.centerY.equalToSuperview()
        }

        contenView.addSubview(presentationStackView)
        presentationStackView.snp.makeConstraints { (builder) in
            builder.top.equalTo(headerImageView.snp.bottom).inset(-Margins.xxLarge)
            builder.left.right.equalToSuperview()
            builder.bottom.equalTo(scrollView.snp.bottom)
        }

    }

    func updateView(presentationResponse: PresentationResponse?) {
        guard let presentationResponse = presentationResponse else { return }

        let firstPresentation = presentationResponse.presentationItems[0]
        titleView.title = presentationResponse.galleryName

        headerImageView.sd_setImage(with: URL(string: firstPresentation.imageSet.fullSize ?? ""), placeholderImage: nil)
        headerTitleLabel.text = presentationResponse.galleryName

        for item in presentationResponse.presentationItems.dropFirst() {

            let sectionImageView = UIImageView()
            sectionImageView.contentMode = .scaleAspectFit
            sectionImageView.clipsToBounds = true

            let sectionCaptionLabel = BaseLabel(withConfiguration: .headline)
            sectionCaptionLabel.text = item.rowCaption

            let sectionView = UIView()
            sectionView.addSubview(sectionImageView)
            sectionView.addSubview(sectionCaptionLabel)

            sectionImageView.sd_setImage(with: URL(string: item.imageSet.defaultImage ?? "")) { [weak self, weak sectionView] (image, error, _, _) in

                guard let strongSelf = self,
                    let sectionView = sectionView,
                    let image = image else { return }

                strongSelf.presentationStackView.addArrangedSubview(sectionView)

                sectionImageView.snp.makeConstraints { (builder) in
                    builder.top.left.bottom.equalToSuperview().inset(Margins.medium)
                    let width:CGFloat = strongSelf.view.frame.size.width / 3
                    builder.width.equalTo(width)
                    builder.height.equalTo(width * (1 / image.aspectRatioValue))

                }

                sectionCaptionLabel.snp.makeConstraints { (builder) in
                    builder.left.equalTo(sectionImageView.snp.right).inset(-Margins.medium)
                    builder.top.right.equalToSuperview().inset(Margins.medium)
                }

            }

        }

    }

}

完成对后端的异步操作后，将在ViewDidLoad和updateView（:)中触发setupView（）。

您可能已经看到，我使用Snapkit来约束我。使用调试器工具检查UI时，出现以下消息：

Scrollable content size is ambiguous for UIScrollView

该问题似乎与UIStackView有关，因为它没有显示。但是，如果我返回并再次推动，则不会出现错误，并且所有内容都可以正确显示。

Answer 1

只需将约束等高和等宽添加到相对于主视图而不是UIScrollView的StackView视图中。换句话说，容器视图的约束与UIScrollView的超级视图相关。

此后，情节提要中将没有警告，您可以继续为子视图添加约束。