创建约束，其中只有尾随锚点可以收缩或扩展

Question

您可以在下面我的 gif 中看到，下面的代码同时生成了左侧和右侧。我想做的只是增加我的右侧。您可以在 gif 中看到红色标记位于我只是想在右侧增加它的一侧。我不知道如何只增加右侧并固定左上侧和下侧。

import UIKit
class ViewController: UIViewController{
    
    var pic = UIView()
    var slizer = UISlider()
    var slidermultiplier: CGFloat = 0.3
    var widthConstraints: NSLayoutConstraint?

    override func viewDidLoad() {
        super.viewDidLoad()
        widthConstraints = pic.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: slidermultiplier)
        
        [pic,slizer].forEach{
            [=10=].translatesAutoresizingMaskIntoConstraints = false
            view.addSubview([=10=])
        }
        NSLayoutConstraint.activate([
            pic.centerYAnchor.constraint(equalTo: view.centerYAnchor),
            pic.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            pic.heightAnchor.constraint(equalTo: view.heightAnchor,multiplier: 0.3),
            widthConstraints!,
            
            slizer.bottomAnchor.constraint(equalTo: view.bottomAnchor),
            slizer.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            slizer.heightAnchor.constraint(equalTo: view.heightAnchor,multiplier: 0.2),
            slizer.widthAnchor.constraint(equalTo: view.widthAnchor,multiplier: 1),
        ])
        
        pic.backgroundColor = .orange
        // changed to .valueChanged
        slizer.addTarget(self, action: #selector(increase), for: .valueChanged)
    }

    @objc func increase() {
        slidermultiplier = CGFloat(slizer.value)
        widthConstraints?.isActive = false
        widthConstraints = pic.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: slidermultiplier)
        widthConstraints?.isActive = true
    }
}

Answer 1

你可以给你的尾随约束大于或等于 0（根据你的需要任何常量）并确保修复前导和其他约束。

Answer 2

正如我在上面的评论中已经提到的，您只需删除 pic.centerYAnchor.constraint(equalTo: view.centerYAnchor) 约束并添加 pic.leadingAnchor.constraint(equalTo: self.view.leadingAnchor, constant: whatver_value_you_think_is_correct) 作为常数，您可以指定您认为完美的任何值。如果不确定要指定什么值，请从 0 开始 :)

override func viewDidLoad() {
        super.viewDidLoad()
        widthConstraints = pic.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: slidermultiplier)

        [pic,slizer].forEach{
            [=10=].translatesAutoresizingMaskIntoConstraints = false
            view.addSubview([=10=])
        }
        NSLayoutConstraint.activate([
            pic.centerYAnchor.constraint(equalTo: view.centerYAnchor),
            pic.leadingAnchor.constraint(equalTo: self.view.leadingAnchor, constant: whatver_value_you_think_is_correct),
            pic.heightAnchor.constraint(equalTo: view.heightAnchor,multiplier: 0.3),
            widthConstraints!,

            slizer.bottomAnchor.constraint(equalTo: view.bottomAnchor),
            slizer.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            slizer.heightAnchor.constraint(equalTo: view.heightAnchor,multiplier: 0.2),
            slizer.widthAnchor.constraint(equalTo: view.widthAnchor,multiplier: 1),
        ])

        pic.backgroundColor = .orange
        // changed to .valueChanged
        slizer.addTarget(self, action: #selector(increase), for: .valueChanged)
    }

您现有的 increase 方法应该可以正常工作

创建约束，其中只有尾随锚点可以收缩或扩展

create constraint where only the trailing anchor can be shrink or expand

swift

slider

nslayoutconstraint

fixed