如何使自动布局约束依赖于多个其他锚点?
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如何使用自动布局使视图的高度等于另外两个视图高度的总和?
例如:
viewA.heightAnchor.constraint(equalTo: ...),
viewB.heightAnchor.constraint(equalTo: ...),
viewC.heightAnchor.constraint(equalTo: viewA.heightAnchor + viewB.heightAnchor)
是否存在不涉及设置常量值并在每个视图边界更改时重新计算的解决方案?
答案
我认为你可以,但只有在一些助手意见的帮助下。看到这个示例的游乐场,我刚刚开始实现这个:
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视图,由顶部的bottomAnchor
和底部的topAnchor
连接。然后,将这些辅助视图的高度设置为等于viewA
和viewB
高度。然后,你的viewC
可以附加到顶视图的topAnchor
和底部视图的bottomAnchor
,这使得viewC
的结果是viewA
的高度加上viewB
的高度。
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