为什么UIButton没有返回正确的约束？

Question

在我的下面的代码中:我在垂直scrollView中添加了5个按钮.每个按钮都被约束到scrollViews的顶部+20,前导,后缘及其高度.我创建了一个b1HeightConstraint变量.它是按住b1按钮的heightConstraint .

在按钮单击中,我正在尝试删除此约束.然而,我面临一个奇怪的问题:

当我记录约束时,我只看到2个约束,即使我已经添加了4个约束.我的视图调试层次结构如下所示:

import UIKit
import Foundation

class ViewController: UIViewController {
    var filterView: UIView!
    var scrollView: UIScrollView!
    var containerView: UIView!

    override func loadView() {
        filterView = UIView()
        view = filterView
        view.backgroundColor = #colorLiteral(red: 0.909803926944733, green: 0.47843137383461, blue: 0.643137276172638, alpha: 1.0)

        scrollView = UIScrollView()
        scrollView.backgroundColor = #colorLiteral(red: 0.474509805440903, green: 0.839215695858002, blue: 0.976470589637756, alpha: 1.0)
        view.addSubview(scrollView)
        scrollView.translatesAutoresizingMaskIntoConstraints = false
        scrollView.topAnchor.constraint(equalTo: view.topAnchor, constant: 0).isActive = true
        scrollView.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
        scrollView.widthAnchor.constraint(equalTo: view.widthAnchor).isActive = true
        scrollView.heightAnchor.constraint(equalTo: view.heightAnchor, multiplier: 1).isActive = true
        scrollView.isScrollEnabled = true

        containerView = UIView()
        containerView.backgroundColor = #colorLiteral(red: 0.176470592617989, green: 0.498039215803146, blue: 0.756862759590149, alpha: 1.0)
        scrollView.addSubview(containerView)
        containerView.translatesAutoresizingMaskIntoConstraints = false

        // This is key:  connect all four edges of the containerView to
        // to the edges of the scrollView
        containerView.topAnchor.constraint(equalTo: scrollView.topAnchor).isActive = true
        containerView.leadingAnchor.constraint(equalTo: scrollView.leadingAnchor).isActive = true
        containerView.trailingAnchor.constraint(equalTo: scrollView.trailingAnchor).isActive = true
        containerView.bottomAnchor.constraint(equalTo: scrollView.bottomAnchor).isActive = true

        // Making containerView and scrollView the same height means the
        // content will not scroll vertically
        containerView.widthAnchor.constraint(equalTo: scrollView.widthAnchor).isActive = true
    }



    let b1 = Buttons(titleText: "one")
    let b2 = Buttons(titleText: "two")
    let b3 = Buttons(titleText: "three")
    let b4 = Buttons(titleText: "four")
    let b5 = Buttons(titleText: "five")
    var b1HeightConstraint : NSLayoutConstraint?

    override func viewDidLoad() {
        super.viewDidLoad()


        let buttonArray = [b1, b2, b3, b4, b5]

        b1.button.addTarget(self, action: #selector(ViewController.shrink(_:)), for: .touchUpInside)

        var startPoint = containerView.topAnchor

        for btn in buttonArray {
            let theBtn = btn.button
            containerView.addSubview(theBtn)
            theBtn.translatesAutoresizingMaskIntoConstraints = false
            theBtn.topAnchor.constraint(equalTo: startPoint, constant: 20).isActive = true
            theBtn.leadingAnchor.constraint(equalTo: containerView.leadingAnchor).isActive = true
            theBtn.trailingAnchor.constraint(equalTo: containerView.trailingAnchor).isActive = true
            theBtn.heightAnchor.constraint(equalTo: scrollView.heightAnchor).isActive = true

            startPoint = theBtn.bottomAnchor
            let btnHeight = theBtn.heightAnchor.constraint(equalTo: scrollView.heightAnchor)
            if btn == b1{
                b1HeightConstraint = btnHeight
            }
        }

        containerView.bottomAnchor.constraint(equalTo: startPoint, constant: 20).isActive = true

    }

    @objc func shrink(_ sender: Any){
        guard let btn = sender as? UIButton else{
            return
        }
        print("count is: \(btn.constraints.count)")

        btn.removeConstraint(b1HeightConstraint!)
        containerView.removeConstraint(b1HeightConstraint!)
        print("count is: \(btn.constraints.count)")
        containerView.updateConstraintsIfNeeded()
        containerView.updateConstraints()
        scrollView.updateConstraintsIfNeeded()
        scrollView.updateConstraints()
    }
}

class Buttons : NSObject {
    let button = UIButton()
    init(titleText: String) {
        button.backgroundColor = #colorLiteral(red: 0.976470589637756, green: 0.850980401039124, blue: 0.549019634723663, alpha: 1.0)
        button.setTitle(titleText, for: .normal)
    }
}

_{代码已准备就绪,只能被转储到ViewController类中.开箱即用.我的代码是这里编写的代码的衍生产品}

Answer 1

以下是有关您的代码的几条评论:

1. 您从未向任何视图添加任何约束,因此您不应删除它们.iOS(CocoaTouch)将这些约束添加到这些视图中,因此请不要触摸它们.(换句话说:当你没有打电话removeConstraint时不要打电话addConstraint).您对约束的控制是激活和停用它们.保留添加和删除 iOS.
2. 激活约束时,会将约束(通过iOS)添加到约束中提到的两个项目的最常见祖先.因此,如果两个视图是兄弟,它将被添加到父级.如果两个视图是父视图和子视图,则约束将添加到父视图.如果两个视图是祖父母和孙子,它将被添加到祖父母.如果两个视图是第一个堂兄弟,则约束将被添加到他们的共同祖父母.

3. 这些代码行:

   let btnHeight = theBtn.heightAnchor.constraint(equalTo: scrollView.heightAnchor)
   if btn == b1{
       b1HeightConstraint = btnHeight
   }
   

   正在创建一个新约束并将其分配给b1HeightConstraint,但您从未激活此约束,因此它根本没有添加到任何视图中.因此,尝试删除它永远不会起作用,因为该约束仅存在于您的b1HeightConstraint属性中.由于它从未被激活,它实际上并没有限制任何东西.

4. 如果要收缩一个按钮,你需要做的其中之一:1)修改constant它的高度约束的财产或 B)的高度约束的设置isActive属性false,然后给它一个新的高度约束或 c)修改的优先级有效约束有自动布局选择使用不同的约束.

5. 在视图调试层次结构中,显示的所有约束都是活动约束(意味着它们可供Auto Layout使用).灰色的是Auto Layout选择不使用的,因为优先级较高的约束优先于它.这不会引起冲突.该self.height = 34 (content size)限制由系统加入到考虑内容压缩和内容拥抱.UIButtons优先抵抗压缩并优先750抵抗扩展250.所述self.height = 34 (content size)约束是灰色的,因为内容拥抱具有的优先级250,并替代地使用另一较高优先级约束(它设置按钮的高度等于该滚动视图的高度优先的约束1000).

更新的代码:

这是您修改过的代码.我改变了两件事:

1. 我确定b1HeightConstraint是一个激活的约束.
2. 我更改了shrink方法以停用旧的高度约束,然后创建并激活一个新的约束.

更新的代码

import UIKit
import Foundation

class ViewController: UIViewController {
    var filterView: UIView!
    var scrollView: UIScrollView!
    var containerView: UIView!

    override func loadView() {
        filterView = UIView()
        view = filterView
        view.backgroundColor = #colorLiteral(red: 0.909803926944733, green: 0.47843137383461, blue: 0.643137276172638, alpha: 1.0)

        scrollView = UIScrollView()
        scrollView.backgroundColor = #colorLiteral(red: 0.474509805440903, green: 0.839215695858002, blue: 0.976470589637756, alpha: 1.0)
        view.addSubview(scrollView)
        scrollView.translatesAutoresizingMaskIntoConstraints = false
        scrollView.topAnchor.constraint(equalTo: view.topAnchor, constant: 0).isActive = true
        scrollView.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
        scrollView.widthAnchor.constraint(equalTo: view.widthAnchor).isActive = true
        scrollView.heightAnchor.constraint(equalTo: view.heightAnchor, multiplier: 1).isActive = true
        scrollView.isScrollEnabled = true

        containerView = UIView()
        containerView.backgroundColor = #colorLiteral(red: 0.176470592617989, green: 0.498039215803146, blue: 0.756862759590149, alpha: 1.0)
        scrollView.addSubview(containerView)
        containerView.translatesAutoresizingMaskIntoConstraints = false

        // This is key:  connect all four edges of the containerView to
        // to the edges of the scrollView
        containerView.topAnchor.constraint(equalTo: scrollView.topAnchor).isActive = true
        containerView.leadingAnchor.constraint(equalTo: scrollView.leadingAnchor).isActive = true
        containerView.trailingAnchor.constraint(equalTo: scrollView.trailingAnchor).isActive = true
        containerView.bottomAnchor.constraint(equalTo: scrollView.bottomAnchor).isActive = true

        // Making containerView and scrollView the same height means the
        // content will not scroll vertically
        containerView.widthAnchor.constraint(equalTo: scrollView.widthAnchor).isActive = true
    }

    let b1 = Buttons(titleText: "one")
    let b2 = Buttons(titleText: "two")
    let b3 = Buttons(titleText: "three")
    let b4 = Buttons(titleText: "four")
    let b5 = Buttons(titleText: "five")
    var b1HeightConstraint : NSLayoutConstraint?

    override func viewDidLoad() {
        super.viewDidLoad()

        let buttonArray = [b1, b2, b3, b4, b5]

        b1.button.addTarget(self, action: #selector(ViewController.shrink(_:)), for: .touchUpInside)

        var startPoint = containerView.topAnchor

        for btn in buttonArray {
            let theBtn = btn.button
            containerView.addSubview(theBtn)
            theBtn.translatesAutoresizingMaskIntoConstraints = false
            theBtn.topAnchor.constraint(equalTo: startPoint, constant: 20).isActive = true
            theBtn.leadingAnchor.constraint(equalTo: containerView.leadingAnchor).isActive = true
            theBtn.trailingAnchor.constraint(equalTo: containerView.trailingAnchor).isActive = true
            //theBtn.heightAnchor.constraint(equalTo: scrollView.heightAnchor).isActive = true

            startPoint = theBtn.bottomAnchor
            let btnHeight = theBtn.heightAnchor.constraint(equalTo: scrollView.heightAnchor)
            btnHeight.isActive = true
            if btn == b1{
                b1HeightConstraint = btnHeight
            }
        }

        containerView.bottomAnchor.constraint(equalTo: startPoint, constant: 20).isActive = true

    }

    @objc func shrink(_ sender: UIButton) {
        b1HeightConstraint?.isActive = false
        b1HeightConstraint = sender.heightAnchor.constraint(equalToConstant: 20)
        b1HeightConstraint?.isActive = true
    }
}

class Buttons : NSObject {
    let button = UIButton()
    init(titleText: String) {
        button.backgroundColor = #colorLiteral(red: 0.976470589637756, green: 0.850980401039124, blue: 0.549019634723663, alpha: 1.0)
        button.setTitle(titleText, for: .normal)
    }
}

缩小按钮高度的选项

1. 设置constant高度约束的属性

   // shrink button's height by 200 points
   b1HeightConstraint?.constant -= 200
   

2. 停用旧约束并创建并激活新约束

   // make button height 20 points
   b1HeightConstraint?.isActive = false
   b1HeightConstraint = sender.heightAnchor.constraint(equalToConstant: 20)
   b1HeightConstraint?.isActive = true
   

3. 更改高度约束的优先级

   // Set b1HeightConstraint's priority to less than 250, and the
   // *content hugging* with priority 250 will take over and resize
   // the button to its intrinsic height
   b1HeightConstraint?.priority = UILayoutPriority(rawValue: 100)
   

   注意:要使其工作,您必须为高度约束赋予初始优先级小于1000(999运行良好),因为如果需要(优先级),自动布局将不允许您更改活动约束的优先级1000.

   要么

   // Just deactivate the buttonHeight constraint and the *content
   // hugging* will take over and it will set the button's height
   // to its intrinsic height
   b1HeightConstraint?.isActive = false