ios - 以编程方式创建布局，使用堆栈 View 和约束不起作用

Question

我正在尝试在 Swift 中以编程方式创建此布局。

https://codepen.io/anon/pen/NXRQbJ

第一个矩形很小。另外两个矩形大小相同，但比第一个矩形大。

这是整个 View Controller 。我没有使用 Storyboard。我的所有代码都在这个 View Controller 中。

import UIKit

class ViewController: UIViewController {

    lazy var stackView: UIStackView = {
        let stackView = UIStackView(arrangedSubviews: [smallRectangleView, bigRectangleView, bigRectangleView2])
        stackView.alignment = .fill
        stackView.distribution = .fillProportionally
        stackView.axis = .vertical
        stackView.translatesAutoresizingMaskIntoConstraints = false
        return stackView
    }()

    var smallRectangleView: UIView = {
        let view = UIView()
        view.backgroundColor = .orange
        view.translatesAutoresizingMaskIntoConstraints = false
        return view
    }()

    var bigRectangleView: UIView = {
        let view = UIView()
        view.backgroundColor = .green
        view.translatesAutoresizingMaskIntoConstraints = false
        return view
    }()

    var bigRectangleView2: UIView = {
        let view = UIView()
        view.backgroundColor = .purple
        view.translatesAutoresizingMaskIntoConstraints = false
        return view
    }()

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        setupLayout()
        print(stackView.frame)
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    func setupLayout() {
        // Stack View
        view.addSubview(stackView)
        stackView.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
        stackView.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
        stackView.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
        stackView.trailingAnchor.constraint(equalTo: view.trailingAnchor).isActive = true

        // Small Recntangle View
        let heightConstraint1 = NSLayoutConstraint(item: smallRectangleView, attribute: .height, relatedBy: .equal, toItem: bigRectangleView, attribute: .height, multiplier: 4.0, constant: 0.0)

        // Big Rectangle View
        let heightConstraint2 = NSLayoutConstraint(item: bigRectangleView, attribute: .height, relatedBy: .equal, toItem: bigRectangleView2, attribute: .height, multiplier: 0.0, constant: 0.0)

        view.addConstraints([heightConstraint1, heightConstraint2])
    }
}

heightConstraint1 和 heightConstraint2 导致错误。我不知道为什么。

// Small Recntangle View
let heightConstraint1 = NSLayoutConstraint(item: smallRectangleView, attribute: .height, relatedBy: .equal, toItem: bigRectangleView, attribute: .height, multiplier: 4.0, constant: 0.0)

// Big Rectangle View
let heightConstraint2 = NSLayoutConstraint(item: bigRectangleView, attribute: .height, relatedBy: .equal, toItem: bigRectangleView2, attribute: .height, multiplier: 0.0, constant: 0.0)

view.addConstraints([heightConstraint1, heightConstraint2])

当我在模拟器上运行这个应用程序时，没有任何显示。这只是一个空白的白色屏幕。此外，在调试器中也存在约束问题。

Answer 1

主要问题似乎是stackView.distribution。我将其从 .fillProportionally 更改为 .fill。我怀疑问题在于，由于您的限制，这些观点已经是相互关联的，从而导致了冲突。

我所做的其他更改，其中一个约束中的乘数需要为0.25而不是4，而在第二个约束中，乘数需要为 1 而不是 0。

我还使用 NSLayoutConstraint.activate 激活最后 2 个约束，而不是将它们添加到 view 中。一般来说，您希望激活约束而不是将它们添加到 View 中。让 iOS 确定将它们添加到哪些 View 。

class ViewController: UIViewController {

    lazy var stackView: UIStackView = {
        let stackView = UIStackView(arrangedSubviews: [smallRectangleView, bigRectangleView, bigRectangleView2])
        stackView.alignment = .fill
        stackView.distribution = .fill
        stackView.axis = .vertical
        stackView.translatesAutoresizingMaskIntoConstraints = false
        return stackView
    }()

    var smallRectangleView: UIView = {
        let view = UIView()
        view.backgroundColor = .orange
        view.translatesAutoresizingMaskIntoConstraints = false
        return view
    }()

    var bigRectangleView: UIView = {
        let view = UIView()
        view.backgroundColor = .green
        view.translatesAutoresizingMaskIntoConstraints = false
        return view
    }()

    var bigRectangleView2: UIView = {
        let view = UIView()
        view.backgroundColor = .purple
        view.translatesAutoresizingMaskIntoConstraints = false
        return view
    }()

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        setupLayout()
        print(stackView.frame)
    }

    func setupLayout() {
        // Stack View
        view.addSubview(stackView)
        stackView.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
        stackView.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
        stackView.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
        stackView.trailingAnchor.constraint(equalTo: view.trailingAnchor).isActive = true

        // Small Recntangle View
        let heightConstraint1 = NSLayoutConstraint(item: smallRectangleView, attribute: .height, relatedBy: .equal, toItem: bigRectangleView, attribute: .height, multiplier: 0.25, constant: 0.0)

        // Big Rectangle View
        let heightConstraint2 = NSLayoutConstraint(item: bigRectangleView, attribute: .height, relatedBy: .equal, toItem: bigRectangleView2, attribute: .height, multiplier: 1.0, constant: 0.0)

        NSLayoutConstraint.activate([heightConstraint1, heightConstraint2])
    }
}