如何使用自动布局使一个 View 的高度等于其他两个 View 高度的总和？

例如:

viewA.heightAnchor.constraint(equalTo: ...),
viewB.heightAnchor.constraint(equalTo: ...),
viewC.heightAnchor.constraint(equalTo: viewA.heightAnchor + viewB.heightAnchor)

是否有一种解决方案不涉及设置常量值并在每次 View 边界更改时重新计算它？

最佳答案

你可以，但我认为只有在一些辅助 View 的帮助下。请参阅我刚刚制作的这个示例 Playground ，它实现了这一点:

import Foundation
import UIKit
import PlaygroundSupport

let vc = UIViewController()
vc.view = UIView()
vc.view.backgroundColor = .white

let viewA = UIView()
let viewB = UIView()
let viewC = UIView()

viewA.backgroundColor = .red
viewB.backgroundColor = .green
viewC.backgroundColor = .blue

viewA.translatesAutoresizingMaskIntoConstraints = false
viewB.translatesAutoresizingMaskIntoConstraints = false
viewC.translatesAutoresizingMaskIntoConstraints = false

vc.view.addSubview(viewA)
vc.view.addSubview(viewB)
vc.view.addSubview(viewC)

let helperViewA = UIView()
let helperViewB = UIView()

helperViewA.translatesAutoresizingMaskIntoConstraints = false
helperViewB.translatesAutoresizingMaskIntoConstraints = false

helperViewA.isHidden = true
helperViewB.isHidden = true

vc.view.addSubview(helperViewA)
vc.view.addSubview(helperViewB)

viewA.bottomAnchor.constraint(equalTo: vc.view.bottomAnchor).isActive = true
viewA.leadingAnchor.constraint(equalTo: vc.view.leadingAnchor).isActive = true
viewA.trailingAnchor.constraint(equalTo: viewB.leadingAnchor).isActive = true
viewA.heightAnchor.constraint(equalToConstant: 20.0).isActive = true

viewB.bottomAnchor.constraint(equalTo: vc.view.bottomAnchor).isActive = true
viewB.widthAnchor.constraint(equalTo: viewA.widthAnchor, multiplier: 1.0).isActive = true
viewB.trailingAnchor.constraint(equalTo: vc.view.trailingAnchor).isActive = true
viewB.heightAnchor.constraint(equalToConstant: 40.0).isActive = true

viewA.heightAnchor.constraint(equalTo: helperViewA.heightAnchor, multiplier: 1.0).isActive = true
viewB.heightAnchor.constraint(equalTo: helperViewB.heightAnchor, multiplier: 1.0).isActive = true

helperViewA.bottomAnchor.constraint(equalTo: helperViewB.topAnchor).isActive = true

viewC.widthAnchor.constraint(equalToConstant: 100).isActive = true
viewC.topAnchor.constraint(equalTo: helperViewA.topAnchor).isActive = true
viewC.bottomAnchor.constraint(equalTo: helperViewB.bottomAnchor).isActive = true


helperViewA.leadingAnchor.constraint(equalTo: viewC.leadingAnchor).isActive = true
helperViewA.trailingAnchor.constraint(equalTo: viewC.trailingAnchor).isActive = true
helperViewB.leadingAnchor.constraint(equalTo: viewC.leadingAnchor).isActive = true
helperViewB.trailingAnchor.constraint(equalTo: viewC.trailingAnchor).isActive = true

viewC.centerXAnchor.constraint(equalTo: vc.view.centerXAnchor).isActive = true
viewC.centerYAnchor.constraint(equalTo: vc.view.centerYAnchor).isActive = true

vc.view.frame.size = CGSize(width: 375, height: 667)
PlaygroundPage.current.liveView = vc.view

这个想法是你有两个垂直堆叠的辅助 View ，由顶部的 bottomAnchor 连接。和底部的 topAnchor .然后，您将这些辅助 View 中的每一个的高度设置为等于您的 viewA和 viewB高度。然后，你的 viewC可以附加到顶 View 的topAnchor和底 View 的 bottomAnchor ，它给出了 viewC 的结果是 viewA 的高度的高度加上viewB的高度。

关于ios - 如何使自动布局约束依赖于多个其他 anchor ？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/49060957/