ios - UIView 内部约束

问题描述

我创建了一个简单的 UIView，它的中心包含一个红色框 (UIImage)。当所有约束都是常量时，代码可以正常工作。但是，如果我将高度约束替换为使框为视图高度一半的高度约束，那么框就会消失。

我认为这要么是因为我做错了（显然），要么我需要做更多的事情来强制约束实现 UIView 高度大于零。

如何设置 redBox 高度约束，使其始终为 BoxView 高度的一半？

import UIKit

class BoxView: UIView {

    public var redBox: UIImageView

    public override init(frame: CGRect) {
        redBox = UIImageView(frame: .zero)
        redBox.backgroundColor = .red

        super.init(frame: frame)
        self.backgroundColor = .yellow

        addSubview(redBox)
        redBox.translatesAutoresizingMaskIntoConstraints = false
        let margins = layoutMarginsGuide
        redBox.centerXAnchor.constraint(equalTo: self.centerXAnchor).isActive = true
        redBox.centerYAnchor.constraint(equalTo: self.centerYAnchor).isActive = true
        redBox.widthAnchor.constraint(equalToConstant: 100).isActive = true
      //redBox.heightAnchor.constraint(equalToConstant: 100).isActive = true
        redBox.heightAnchor.constraint(equalTo: self.heightAnchor, constant: 0.5)
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        view = BoxView()
    }
}

标签： iosswiftuiviewconstraints

代替

redBox.heightAnchor.constraint(equalTo: self.heightAnchor, constant: 0.5)

和

redBox.heightAnchor.constraint(equalTo: self.heightAnchor, multiplier: 0.5).isActive = true

NSLayoutConstraint.activate([
    redBox.centerXAnchor.constraint(equalTo: self.centerXAnchor),
    redBox.centerYAnchor.constraint(equalTo: self.centerYAnchor),
    redBox.widthAnchor.constraint(equalToConstant: 100),
    redBox.heightAnchor.constraint(equalTo: self.heightAnchor, multiplier: 0.5)
])

在您当前的代码中，首先您错过了.isActive = true与该行不存在具有相同效果的那个，如果指定，这将使框高度等于视图的高度+常量（= 0.5）

盒子高度 = 视图高度 * 乘数 + 常数

并且由于默认乘数 = 1 并且您设置常量 = 0.5 这将是

盒子高度 = 视图高度 * 1.0 + 0.5

但相反，你需要

box height = view height * 0.5 + 0 // 在约束中省略 consatnt 它将为零

class BoxView: UIView { 
    public var redBox: UIImageView
    public override init(frame: CGRect) {
        super.init(frame: frame)
        redBox = UIImageView(frame: .zero)
        redBox.backgroundColor = .red
        self.backgroundColor = .yellow
        addSubview(redBox)
        redBox.translatesAutoresizingMaskIntoConstraints = false
        let margins = layoutMarginsGuide

        NSLayoutConstraint.activate([
            redBox.centerXAnchor.constraint(equalTo: self.centerXAnchor),
            redBox.centerYAnchor.constraint(equalTo: self.centerYAnchor),
            redBox.widthAnchor.constraint(equalToConstant: 100),
            redBox.heightAnchor.constraint(equalTo: self.heightAnchor, multiplier: 0.5)
        ])
    }
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

ios - UIView 内部约束

问题描述

解决方案

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