ios - 以编程方式设置带有约束的 UIScrollView 的正确方法？

Question

我正在尝试使用约束以编程方式在并排放置的两个 View Controller 之间创建一个简单的水平滚动。我这里的内容似乎有效，但我读过的所有内容都表明，如果约束设置正确，我不需要配置 contentSize 的大小——autolayout 会为我做这件事。但是当我从 viewWillLayoutSubviews 中删除 scrollView.contentSize = CGSize(width: view.bounds.width * 2, height: view.bounds.height) 时，它不会滚动.我哪里出错了？

class ViewController0: UIViewController {


    let scrollView = UIScrollView()
    let contentView = UIView()
    let page1 = ViewController1()
    let page2 = ViewController2()


    override func loadView() {

        setView()
        addScrollView()
        fillScrollView()

    }


    override func viewDidLoad() {
        super.viewDidLoad()
    }


    override func viewWillLayoutSubviews() {
        super.viewWillLayoutSubviews()

        scrollView.contentSize = CGSize(width: view.bounds.width * 2, height: view.bounds.height)

    }


    func setView() {

        view = UIView()
        view.frame = UIScreen.main.bounds
        view.backgroundColor = UIColor.blue

    }


    func addScrollView() {

        scrollView.bounces = false
        scrollView.isPagingEnabled = true
        scrollView.backgroundColor = UIColor.brown
        scrollView.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(scrollView)

        scrollView.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
        scrollView.trailingAnchor.constraint(equalTo: view.trailingAnchor).isActive = true
        scrollView.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
        scrollView.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true

        contentView.backgroundColor = UIColor.green
        contentView.translatesAutoresizingMaskIntoConstraints = false
        scrollView.addSubview(contentView)

        contentView.leadingAnchor.constraint(equalTo: scrollView.leadingAnchor).isActive = true
        contentView.topAnchor.constraint(equalTo: scrollView.topAnchor).isActive = true
        contentView.heightAnchor.constraint(equalTo: view.heightAnchor, multiplier: 1).isActive = true
        contentView.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 2).isActive = true

    }


    func fillScrollView() {

        addChildViewController(page1)
        page1.didMove(toParentViewController: self)
        page1.view.translatesAutoresizingMaskIntoConstraints = false
        contentView.addSubview(page1.view)
        page1.view.leadingAnchor.constraint(equalTo: contentView.leadingAnchor).isActive = true
        page1.view.topAnchor.constraint(equalTo: contentView.topAnchor).isActive = true
        page1.view.bottomAnchor.constraint(equalTo: contentView.bottomAnchor).isActive = true
        page1.view.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 1).isActive = true

        addChildViewController(page2)
        page2.didMove(toParentViewController: self)
        page2.view.translatesAutoresizingMaskIntoConstraints = false
        contentView.addSubview(page2.view)
        page2.view.leadingAnchor.constraint(equalTo: page1.view.trailingAnchor).isActive = true
        page2.view.topAnchor.constraint(equalTo: contentView.topAnchor).isActive = true
        page2.view.bottomAnchor.constraint(equalTo: contentView.bottomAnchor).isActive = true
        page2.view.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 1).isActive = true

    }


}

Answer 1

这应该可行

    class ViewController0: UIViewController {

    let scrollView = UIScrollView()
    let page1 = ViewController1()
    let page2 = ViewController1()

    override func loadView() {
        setView()
        addScrollView()
        setupPage()
    }

    func setView() {

        view = UIView()
        view.frame = UIScreen.main.bounds
        view.backgroundColor = UIColor.blue

    }

    func addScrollView() {

        scrollView.backgroundColor = UIColor.brown
        scrollView.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(scrollView)
        scrollView.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
        scrollView.trailingAnchor.constraint(equalTo: view.trailingAnchor).isActive = true
        scrollView.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
        scrollView.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
    }

    func setupPage() {
        page1.view.translatesAutoresizingMaskIntoConstraints = false
        scrollView.addSubview(page1.view)
        addChildViewController(page1)
        page1.didMove(toParentViewController: self)

        page2.view.translatesAutoresizingMaskIntoConstraints = false
        scrollView.addSubview(page2.view)
        addChildViewController(page2)
        page2.didMove(toParentViewController: self)

        let views: [String: UIView] = ["view": view, "page1": page1.view, "page2": page2.view]
        let verticalConstraints = NSLayoutConstraint.constraints(withVisualFormat: "V:|[page1(==view)]|", options: [], metrics: nil, views: views)
        let horizontalConstraints = NSLayoutConstraint.constraints(withVisualFormat: "H:|[page1(==view)][page2(==view)]|", options: [.alignAllTop, .alignAllBottom], metrics: nil, views: views)

        NSLayoutConstraint.activate(verticalConstraints + horizontalConstraints)
    }

}