ios - 为什么在 UIScrollView 中看不到 UIStackView？

Question

我要把 UIStackView 放在 UIScrollView 中。更简单地说，我要做一张思维导图。我放入UIScrollView中的UIStackView是思维导图的一个对象。因此，嵌入的 UIStackView 将出现在 UIScrollView 的所有区域中。

但是，虽然我已经为UIScrollView指定了UIStackView的位置，但是UIStackView并没有出现在UIScrollView中。

我的界面构建器(附加界面构建器图像以了解我的 View 层次结构。):

import UIKit

class ViewController: UIViewController {
    @IBOutlet weak var scrollView: UIScrollView!
    @IBOutlet weak var createObject: UIBarButtonItem!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        let redView = UIView()
        redView.backgroundColor = .red

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

        let stackView = UIStackView(arrangedSubviews: [redView, blueView])
        stackView.axis = .vertical
        stackView.distribution = .fillEqually

        stackView.center = scrollView.center

        scrollView.addSubview(stackView)
    }
}

Answer 1

UIView 和 UIStackView 都没有固有大小。

因此，您最终会向 ScrollView 添加一个大小为 0, 0 的堆栈 View ，其中包含两个 View ，每个 View 的大小均为 0, 0。

您需要在某处应用一些尺寸。

这将为您提供一个堆栈 View ，其宽度与 ScrollView 相同，高度是 ScrollView 的两倍(因此您有一个“全高”蓝色 View 和一个“全高”红色 View ):

class ViewController: UIViewController {

    @IBOutlet weak var scrollView: UIScrollView!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        let redView = UIView()
        redView.backgroundColor = .red

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

        let stackView = UIStackView(arrangedSubviews: [redView, blueView])
        stackView.axis = .vertical
        stackView.distribution = .fillEqually

        scrollView.addSubview(stackView)

        stackView.translatesAutoresizingMaskIntoConstraints = false

        NSLayoutConstraint.activate([
            stackView.topAnchor.constraint(equalTo: scrollView.topAnchor, constant: 0.0),
            stackView.bottomAnchor.constraint(equalTo: scrollView.bottomAnchor, constant: 0.0),
            stackView.leadingAnchor.constraint(equalTo: scrollView.leadingAnchor, constant: 0.0),
            stackView.trailingAnchor.constraint(equalTo: scrollView.trailingAnchor, constant: 0.0),

            stackView.widthAnchor.constraint(equalTo: scrollView.widthAnchor, constant: 0.0),
            stackView.heightAnchor.constraint(equalTo: scrollView.heightAnchor, multiplier: 2.0),
            ])

    }
}

---

编辑:

这是另一个例子。它添加了 6 个具有指定宽度和高度的 subview 。堆栈 View 属性更改为:

.alignment = .center
.distribution = .fill
.spacing = 8

结果:

向下滚动:

和代码:

class ViewController: UIViewController {

    @IBOutlet weak var scrollView: UIScrollView!

    override func viewDidLoad() {
        super.viewDidLoad()

        let colors: [UIColor] = [
            .red,
            .blue,
            .green,
            .orange,
            .yellow,
            .cyan,
        ]

        let sizes: [CGSize] = [
            CGSize(width: 100, height: 150),
            CGSize(width: 250, height: 100),
            CGSize(width: 200, height: 120),
            CGSize(width: 160, height: 200),
            CGSize(width: 220, height: 180),
            CGSize(width:  60, height:  80),
        ]

        let stackView = UIStackView()
        stackView.axis = .vertical
        stackView.distribution = .fill
        stackView.alignment = .center
        stackView.spacing = 8

        for (color, size) in zip(colors, sizes) {
            let v = UIView()
            v.translatesAutoresizingMaskIntoConstraints = false
            v.widthAnchor.constraint(equalToConstant: size.width).isActive = true
            v.heightAnchor.constraint(equalToConstant: size.height).isActive = true
            v.backgroundColor = color
            stackView.addArrangedSubview(v)
        }

        scrollView.addSubview(stackView)

        stackView.translatesAutoresizingMaskIntoConstraints = false

        NSLayoutConstraint.activate([
            stackView.topAnchor.constraint(equalTo: scrollView.topAnchor, constant: 0.0),
            stackView.bottomAnchor.constraint(equalTo: scrollView.bottomAnchor, constant: 0.0),
            stackView.leadingAnchor.constraint(equalTo: scrollView.leadingAnchor, constant: 0.0),
            stackView.trailingAnchor.constraint(equalTo: scrollView.trailingAnchor, constant: 0.0),

            stackView.widthAnchor.constraint(equalTo: scrollView.widthAnchor, constant: 0.0),

            // do NOT set a heightAnchor ... let the subviews define the height
//          stackView.heightAnchor.constraint(equalTo: scrollView.heightAnchor, multiplier: 2.0),
            ])

    }
}