为什么UIButton没有返回正确的约束？

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。 它是在那里保持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，只能在ViewController类中转储。 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： 当你没有调用addConstraint时不要调用removeConstraint ）。 您对约束的控制是激活和停用它们。 将添加和删除留给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，它将被添加到父视图。 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. 如果要缩小按钮，则需要执行以下操作之一：a）修改其高度约束的constant属性或 b）将其高度约束的isActive属性设置为false ，然后为其赋予新的高度约束或者 c）修改自动布局选择使用不同约束的活动约束的优先级。

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。 系统添加self.height = 34 (content size)约束以考虑内容压缩和内容拥抱 。 UIButton的抗压优先级为750 ，抗冲击优先级为250 。 self.height = 34 (content size)约束显示为灰色，因为内容拥抱的优先级为250而另一个使用了更高优先级的约束（将按钮的高度设置为等于scrollView的高度的约束优先级为1000 ）。

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更新的代码：

这是您修改过的代码。 我改变了两件事：

1. 我确保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) } } 

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缩小按钮高度的选项

1. 设置高度约束的constant属性

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

2. 停用旧约束并创建并激活一个新约束

    // 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小于1000的初始优先级（ 999可以正常工作），因为如果需要， Auto Layout将不允许您更改活动约束的优先级（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 

Answer 2

这是因为视图及其superView之间的约束被添加到superView，如果它们是静态添加到UIButton ，则只能看到高度/宽度约束，请从Vandad IOS Book查看此图

看到这个演示