如何更新 swift 中的锚约束

Question

我想在 iOS 中创建一个类似于 android 的菜单。我正在使用 布局约束 来设置约束。我在尝试更新单击按钮时图像的左侧 constraint 时遇到了问题（它应该根据单击按钮的位置设置动画）。谁能帮我？它应该支持横向和纵向。

我不想使用第三方代码，也不想使用 NSLayoutconstraint。

这是我的代码。

class MenuViewController: UIViewController {
            var buttons: [UIButton] = []
            var imageView : UIImageView!

            override func viewDidLoad() {
                super.viewDidLoad()
            }

            override func viewDidAppear(_ animated: Bool) {
                super.viewDidAppear(animated)
                addMenuItems()
            }

            func addMenuItems() {

                for _ in 0...4 {
                    let button : UIButton = UIButton()
                    self.view.addSubview(button)
                    button.backgroundColor = UIColor.darkGray
                    button.addTarget(self, action: #selector(didSelectedButton(_:)), for: .touchUpInside)
                    self.buttons.append(button)

                }

                for (index, button) in buttons.enumerated() {

                    button.setTitle(" \(index)", for: .normal)
                    if index == 0 {
                        button.translatesAutoresizingMaskIntoConstraints = false
                        button.leftAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.leftAnchor, constant: 0).isActive = true
                        button.widthAnchor.constraint(greaterThanOrEqualToConstant: 1).isActive = true
                        button.heightAnchor.constraint(equalToConstant: 50).isActive = true
                        button.topAnchor.constraint(equalTo: self.view.topAnchor, constant:200).isActive = true

                        self.imageView = UIImageView()
                        self.view.addSubview(self.imageView)
                        self.imageView.backgroundColor = UIColor.red

                        self.imageView.translatesAutoresizingMaskIntoConstraints = false
                        self.imageView.leftAnchor.constraint(equalTo: button.leftAnchor, constant: 0).isActive = true
                        self.imageView.widthAnchor.constraint(equalTo: button.widthAnchor, multiplier: 1).isActive = true
                        self.imageView.heightAnchor.constraint(equalToConstant: 4).isActive = true
                        self.imageView.topAnchor.constraint(equalTo: self.view.topAnchor, constant:250).isActive = true

                    }
                    else {

                        let preButton = buttons\[index - 1\]
                        button.translatesAutoresizingMaskIntoConstraints = false
                        button.leftAnchor.constraint(equalTo: preButton.rightAnchor, constant: 0).isActive = true
                        button.widthAnchor.constraint(equalTo: preButton.widthAnchor, multiplier: 1).isActive = true
                        button.heightAnchor.constraint(equalToConstant: 50).isActive = true
                        button.topAnchor.constraint(equalTo: self.view.topAnchor, constant:200).isActive = true
                        if index == self.buttons.count - 1 {
                            button.rightAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.rightAnchor, constant: 0).isActive = true
                        }
                    }

                }

            }

            @objc func didSelectedButton(_ button:UIButton) {
                UIView.animate(withDuration: 1, animations: {
                    self.imageView.leftAnchor.constraint(equalTo: button.leftAnchor).isActive = true
                    self.imageView.layoutIfNeeded()
                }, completion: nil)
            }

        }

Answer 1

使用锚点创建 NSLayoutContraints。创建新的需要停用之前的。

将此属性添加到您的 MenuViewController:

var imageLeftConstraint: NSLayoutConstraint?

第一次创建约束时设置它：

imageLeftConstraint = self.imageView.leftAnchor.constraint(equalTo: button.leftAnchor, constant: 0)
imageLeftConstraint?.isActive = true

然后在添加新约束之前使用它来停用先前的约束：

@objc func didSelectedButton(_ button:UIButton) {
    imageLeftConstraint?.isActive = false
    imageLeftConstraint = self.imageView.leftAnchor.constraint(equalTo: button.leftAnchor)
    imageLeftConstraint?.isActive = true
    UIView.animate(withDuration: 1, animations: {
        self.view.layoutIfNeeded()
    }, completion: nil)
}

注意：你需要在imageView（又名self.view）的superView上调用layoutIfNeeded()，因为[=18之间的约束=] 和 imageView 将添加到它们的共同祖先 (self.view)。

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