ios - 以编程方式布置 UIScrollView，并为其 subview 添加自动布局，但它不滚动

Question

我试图弄清楚 UIScrollView 是如何工作的，我向它添加了一些具有不同 backgroundColor 属性的 subview 。我用 ios9 autolayout 布置了 subview ，但即使 View 在屏幕之外，UIScrollView 仍然不会滚动。

import UIKit

class ViewController: UIViewController {

    let scrollView: UIScrollView = {
        let sv = UIScrollView()
        sv.translatesAutoresizingMaskIntoConstraints = false
        sv.backgroundColor = .gray
        return sv
    }()

    override func viewDidLoad() {
        super.viewDidLoad()

        view.addSubview(scrollView)

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

        let view1 = UIView()
        view1.backgroundColor = .red

        let view2 = UIView()
        view2.backgroundColor = .blue

        let view3 = UIView()
        view3.backgroundColor = .green

        let view4 = UIView()
        view4.backgroundColor = .purple

        let views = [view1, view2, view3, view4]

        for view in views {
            scrollView.addSubview(view)
            view.translatesAutoresizingMaskIntoConstraints = false
        }

        view1.topAnchor.constraint(equalTo: scrollView.topAnchor).isActive = true
        view1.leftAnchor.constraint(equalTo: scrollView.leftAnchor).isActive = true
        view1.heightAnchor.constraint(equalToConstant: 140).isActive = true
        view1.widthAnchor.constraint(equalToConstant: 140).isActive = true

        view2.topAnchor.constraint(equalTo: view1.bottomAnchor, constant: 100).isActive = true
        view2.leftAnchor.constraint(equalTo: view1.rightAnchor).isActive = true
        view2.heightAnchor.constraint(equalToConstant: 140).isActive = true
        view2.widthAnchor.constraint(equalToConstant: 140).isActive = true

        view3.topAnchor.constraint(equalTo: view2.bottomAnchor, constant: 50).isActive = true
        view3.leftAnchor.constraint(equalTo: view1.rightAnchor).isActive = true
        view3.heightAnchor.constraint(equalToConstant: 140).isActive = true
        view3.widthAnchor.constraint(equalToConstant: 140).isActive = true

        view4.topAnchor.constraint(equalTo: view3.bottomAnchor, constant: 20).isActive = true
        view4.leftAnchor.constraint(equalTo: view1.rightAnchor).isActive = true
        view4.heightAnchor.constraint(equalToConstant: 140).isActive = true
        view4.widthAnchor.constraint(equalToConstant: 140).isActive = true
    }

}

Answer 1

在 UIScrollViews 中使用自动布局时，您必须将 subview 固定到 ScrollView 的顶部和底部，这样 ScrollView 才能计算其 contentSize。

添加这一行修复它:

view4.bottomAnchor.constraint(equalTo: scrollView.bottomAnchor, constant: 0).isActive = true