ios - UI 元素在 UIScrollView swift 中不起作用

Question

我正在创建一个 ScrollView ，并在 ScrollView 中添加了一个 UIView。然而，在 uiview 上设置的每个属性(如颜色)都不会显示。我将 UIView 的背景设置为蓝色但不显示。我不知道我是否做错了什么，下面是我的代码

let scrollView: UIScrollView = {
        let srv = UIScrollView()
        srv.translatesAutoresizingMaskIntoConstraints = false
        return srv
    }()
    let contentView: UIView = {
        let cview = UIView()
        cview.backgroundColor = .blue
        cview.translatesAutoresizingMaskIntoConstraints = false
        return cview
    }()

在我的 viewDidLoad 中我添加了这个

view.addSubview(scrollView)
scrollView.addSubview(contentView)

NSLayoutConstraint.activate([
    scrollView.centerXAnchor.constraint(equalTo: view.centerXAnchor),
    scrollView.widthAnchor.constraint(equalTo: view.widthAnchor),
    scrollView.topAnchor.constraint(equalTo: view.topAnchor),
    scrollView.bottomAnchor.constraint(equalTo: view.bottomAnchor),

    contentView.centerXAnchor.constraint(equalTo: scrollView.centerXAnchor),
    contentView.widthAnchor.constraint(equalTo: scrollView.widthAnchor),
    contentView.topAnchor.constraint(equalTo: scrollView.topAnchor),
    contentView.bottomAnchor.constraint(equalTo: scrollView.bottomAnchor),])

Answer 1

scrollview 期望它的大小来自它的 content ，所以设置宽度和高度到 contentView 相对于主外部 View

NSLayoutConstraint.activate([
    scrollView.centerXAnchor.constraint(equalTo: view.centerXAnchor),
    scrollView.widthAnchor.constraint(equalTo: view.widthAnchor),
    scrollView.topAnchor.constraint(equalTo: view.topAnchor),
    scrollView.bottomAnchor.constraint(equalTo: view.bottomAnchor),

    contentView.leadingAnchor.constraint(equalTo: scrollView.leadingAnchor),
    contentView.trailingAnchor.constraint(equalTo: scrollView.trailingAnchor),
    contentView.topAnchor.constraint(equalTo: scrollView.topAnchor),
    contentView.bottomAnchor.constraint(equalTo: scrollView.bottomAnchor)
    contentView.widthAnchor.constraint(equalTo: view.widthAnchor),
    contentView.heightAnchor.constraint(equalTo: view.heightAnchor,multiplier:2.0)
])