在视图中发现未知约束

Question

我正在创建自定义 class 以使视图可扩展； class 与修改视图高度限制的 UIPanGestureRecognizer 一起使用。在调试代码时，我使用以下代码来显示与视图关联的高度限制。

print(self.constraints.filter({ [=10=].firstAttribute == .height}).map{print("costraints \([=10=])")})

奇怪的是，除了扩展视图的方法创建的约束之外，还有一个我不知道从哪里来的约束。这是控制台中打印的内容：

constraint <NSAutoresizingMaskLayoutConstraint:0x6140002828f0 h=--& v=--& UIStackView:0x7ff1c871d0e0.height == 190   (active)>
constraint <NSLayoutConstraint:0x60800009c160 PhotoMapping.ExpandableView:0x7ff1c8416fa0.height == 100   (active)>

这是 class 的完整代码。

import Foundation
import UIKit

class ExpandableView: UIView {
    let panGestureRecognizer = UIPanGestureRecognizer()
    var minHeight: CGFloat = 0 {
        didSet {
            initialHeight = minHeight
        }
    }
    var maxHeight: CGFloat = 0
    var initialHeight: CGFloat = 0
    var initialPoint: CGPoint? = nil

    var heightConstraintConstant: CGFloat {
        get {
            if !self.constraints.filter({ [=12=].firstAttribute == .height}).isEmpty {
                return self.constraints.filter({[=12=].firstAttribute == .height && [=12=].secondItem == nil}).first!.constant
            } else {
                let constrain = NSLayoutConstraint(item: self, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .height, multiplier: 1.0, constant: initialHeight)
                self.addConstraint(constrain)
                return constrain.constant
            }
        }

        set(newConstant){
            if !self.constraints.filter({ [=12=].firstAttribute == .height}).isEmpty {
                self.constraints.filter({[=12=].firstAttribute == .height && [=12=].secondItem == nil}).first?.constant = newConstant
                self.constraints.filter({[=12=].firstAttribute == .height && [=12=].secondItem == nil}).map{print("constant \([=12=].constant)")}
            } else {
                let constrain = NSLayoutConstraint(item: self, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .height, multiplier: 1.0, constant: newConstant)
                self.addConstraint(constrain)
            }
            self.layoutIfNeeded()
        }

    }

    func initialize(minHeight: CGFloat, maxHeight: CGFloat) {
        panGestureRecognizer.addTarget(self, action: #selector(handlePan(_:)))
        panGestureRecognizer.minimumNumberOfTouches = 1
        panGestureRecognizer.maximumNumberOfTouches = 1
        self.addGestureRecognizer(panGestureRecognizer)
        self.minHeight = minHeight
        self.maxHeight = maxHeight
    }

    @objc func handlePan(_ sender: Any) {
        let translation = panGestureRecognizer.translation(in: self)

        if initialPoint == nil {
            initialPoint = translation
        }

        let translationHeight = CGFloat(translation.y - initialPoint!.y)
        print("translationHeight: \(translationHeight)")

        if panGestureRecognizer.state == .changed {
            let finalHeight = translationHeight + initialHeight
            print("finalHeight: \(finalHeight)")
            if finalHeight <= maxHeight && finalHeight >= minHeight {
                heightConstraintConstant = finalHeight
            }
        } else if panGestureRecognizer.state == .ended {

            let mediumY = maxHeight / 2 + minHeight / 2

            if translation.y <= 0 {
                heightConstraintConstant = minHeight
            } else if translationHeight >= maxHeight {
                heightConstraintConstant = minHeight
            } else if heightConstraintConstant >= mediumY {

                UIView.animate(withDuration: 0.4) {
                    self.heightConstraintConstant = self.maxHeight
                    self.layoutIfNeeded()
                }

            } else if heightConstraintConstant <= mediumY {

                UIView.animate(withDuration: 0.2) {
                    self.heightConstraintConstant = self.minHeight
                    self.layoutIfNeeded()
                }
            }

            initialPoint = nil
            initialHeight = heightConstraintConstant
        }

        layoutIfNeeded()
    }

}

我在 storyBoard 中将视图的 class 设置为 "ExpandableView" 并在 superclass viewController 中对其进行了初始化，如下所示：这是 ViewController 中的代码，我在其中初始化名为 profileView 的视图。

profileView.isUserInteractionEnabled = true
profileView.initialize(minHeight: 100, maxHeight: 190)

Answer 1

将您的视图 translatesAutoresizingMaskIntoConstraints 设置为 false。

当它是 true 时，它将创建一些定义其位置和大小的约束。

Answer 2

发现错误。第二个约束来自视图本身内部的 UIStackView。我只需要设置 stackView.translatesAutoresizingMaskIntoConstraints = false 就可以解决问题。

Answer 3

您看到的意外约束是 NSAutoresizingMaskLayoutConstraint 的一个实例。这是因为您以编程方式添加了一个组件（它似乎是 UIStackView 的一个实例）并且您没有将其 translatesAutoResizingMaskIntoConstraints 属性设置为 false)

在视图中发现未知约束

Unknow constrain found inside a view

constraints

ios

uipangesturerecognizer

swift