Question

尝试找到更新事件中多个UI元素的多个约束的解决方案。我已经看到了一些停用，进行更改，然后重新激活约束的示例，这种方法似乎对我正在使用的24个锚点不切实际。

我的一组更改：

ticketContainer.translatesAutoresizingMaskIntoConstraints = false
ticketContainer.topAnchor.constraintEqualToAnchor(self.topAnchor).active = true
ticketContainer.leftAnchor.constraintEqualToAnchor(self.rightAnchor, constant: 20).active = true
ticketContainer.widthAnchor.constraintEqualToConstant(200.0).active = true

ticketContainer.leftAnchor.constraintEqualToAnchor(self.leftAnchor, constant: 20).active = true
ticketContainer.widthAnchor.constraintEqualToConstant(100.0).active = true

Answer 1

您是否尝试将使用布局锚点创建的相关约束保存到属性，然后只更改常量？ E.g。

var ticketTop : NSLayoutConstraint?

func setup() {
    ticketTop = ticketContainer.topAnchor.constraintEqualToAnchor(self.topAnchor, constant:100)
    ticketTop.active = true
}

func update() {
    ticketTop?.constant = 25
}

可能更优雅

根据您对编写扩展程序的喜好，以下是一种可能更优雅的方法，它不使用属性，而是在NSLayoutAnchor和UIView上创建扩展方法，以帮助更简洁地使用。< / p>

首先，你会在NSLayoutAnchor上写一个扩展名，如下所示：

extension NSLayoutAnchor {
    func constraintEqualToAnchor(anchor: NSLayoutAnchor!, constant:CGFloat, identifier:String) -> NSLayoutConstraint! {
        let constraint = self.constraintEqualToAnchor(anchor, constant:constant)
        constraint.identifier = identifier
        return constraint
    }
}

此扩展允许您在从锚创建它的同一方法调用中为约束设置标识符。请注意，Apple文档暗示XAxis锚点（左，右，前导等）不允许您使用YAxis锚点（顶部，底部等）创建约束，但我不认为这实际上是真的。如果您确实需要这种类型的编译器检查，则需要为NSLayoutXAxisAnchor，NSLayoutYAxisAnchor和NSLayoutDimension（对于宽度和高度约束）编写单独的扩展，以强制执行同轴锚点类型要求。

接下来，您将在UIView上编写一个扩展名来获取标识符的约束：

extension UIView {
    func constraint(withIdentifier:String) -> NSLayoutConstraint? {
        return self.constraints.filter{ $0.identifier == withIdentifier }.first
    }
}

有了这些扩展程序，您的代码就会变成：

func setup() {
    ticketContainer.topAnchor.constraintEqualToAnchor(self.topAnchor, constant:100, identifier:"ticketTop").active = true
}

func update() {
    self.constraint(withIdentifier:"ticketTop")?.constant = 25
}

请注意，对于标识符使用常量或枚举而不是魔术字符串名称将是对上述内容的改进，但我保持此答案的简要和重点。

Answer 2

您可以迭代视图的约束并检查匹配的项目和锚点。请记住，约束将在视图的超视图上，除非它是一个尺寸约束。我编写了一些帮助代码，允许您在视图的一个锚点上找到所有约束。

import UIKit

class ViewController: UIViewController {

    let label = UILabel()
    let imageView = UIImageView()

    override func viewDidLoad() {
        super.viewDidLoad()

        label.text = "Constraint finder"

        label.translatesAutoresizingMaskIntoConstraints = false
        imageView.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(label)
        view.addSubview(imageView)

        label.topAnchor.constraint(equalTo: view.topAnchor, constant: 30).isActive = true
        label.leftAnchor.constraint(equalTo: view.leftAnchor, constant: 20).isActive = true
        label.widthAnchor.constraint(greaterThanOrEqualToConstant: 50).isActive = true

        imageView.topAnchor.constraint(equalTo: label.bottomAnchor).isActive = true
        imageView.leftAnchor.constraint(equalTo: view.leftAnchor, constant: 60).isActive = true
        imageView.widthAnchor.constraint(equalTo: label.widthAnchor).isActive = true
        imageView.heightAnchor.constraint(equalToConstant: 70).isActive = true

        print("Label's top achor constraints: \(label.constraints(on: label.topAnchor))")
        print("Label's width achor constraints: \(label.constraints(on: label.widthAnchor))")
        print("ImageView's width achor constraints: \(imageView.constraints(on: imageView.widthAnchor))")
    }

}

public extension UIView {

    public func constraints(on anchor: NSLayoutYAxisAnchor) -> [NSLayoutConstraint] {
        guard let superview = superview else { return [] }
        return superview.constraints.filtered(view: self, anchor: anchor)
    }

    public func constraints(on anchor: NSLayoutXAxisAnchor) -> [NSLayoutConstraint] {
        guard let superview = superview else { return [] }
        return superview.constraints.filtered(view: self, anchor: anchor)
    }

    public func constraints(on anchor: NSLayoutDimension) -> [NSLayoutConstraint] {
        guard let superview = superview else { return [] }
        return constraints.filtered(view: self, anchor: anchor) + superview.constraints.filtered(view: self, anchor: anchor)
    }

}

extension NSLayoutConstraint {

    func matches(view: UIView, anchor: NSLayoutYAxisAnchor) -> Bool {
        if let firstView = firstItem as? UIView, firstView == view && firstAnchor == anchor {
            return true
        }
        if let secondView = secondItem as? UIView, secondView == view && secondAnchor == anchor {
            return true
        }
        return false
    }

    func matches(view: UIView, anchor: NSLayoutXAxisAnchor) -> Bool {
        if let firstView = firstItem as? UIView, firstView == view && firstAnchor == anchor {
            return true
        }
        if let secondView = secondItem as? UIView, secondView == view && secondAnchor == anchor {
            return true
        }
        return false
    }

    func matches(view: UIView, anchor: NSLayoutDimension) -> Bool {
        if let firstView = firstItem as? UIView, firstView == view && firstAnchor == anchor {
            return true
        }
        if let secondView = secondItem as? UIView, secondView == view && secondAnchor == anchor {
            return true
        }
        return false
    }
}

extension Array where Element == NSLayoutConstraint {

    func filtered(view: UIView, anchor: NSLayoutYAxisAnchor) -> [NSLayoutConstraint] {
        return filter { constraint in
            constraint.matches(view: view, anchor: anchor)
        }
    }
    func filtered(view: UIView, anchor: NSLayoutXAxisAnchor) -> [NSLayoutConstraint] {
        return filter { constraint in
            constraint.matches(view: view, anchor: anchor)
        }
    }
    func filtered(view: UIView, anchor: NSLayoutDimension) -> [NSLayoutConstraint] {
        return filter { constraint in
            constraint.matches(view: view, anchor: anchor)
        }
    }

}

Answer 3

定位单个视图

extension UIView {
    func add(view: UIView, left: CGFloat, right: CGFloat, top: CGFloat, bottom: CGFloat) {

        view.translatesAutoresizingMaskIntoConstraints = false
        self.addSubview(view)

        view.leftAnchor.constraint(equalTo: self.leftAnchor, constant: left).isActive = true
        view.rightAnchor.constraint(equalTo: self.rightAnchor, constant: right).isActive = true

        view.topAnchor.constraint(equalTo: self.topAnchor, constant: top).isActive = true
        view.bottomAnchor.constraint(equalTo: self.bottomAnchor, constant: bottom).isActive = true

    }
}

用法

headerView.add(view: headerLabel, left: 20, right: 0, top: 0, bottom: 0)

Answer 4

我找到了另一种解决方案。如果要更改通过Interface Builder添加的现有约束，则实际上需要迭代超级视图的约束。尝试更改路线约束的常数值时，至少是这样。

下面的示例显示了底部对齐方式，但是我假设相同的代码也可以用于前导/后退/顶部对齐。

    private func bottomConstraint(view: UIView) -> NSLayoutConstraint {
        guard let superview = view.superview else {
            return NSLayoutConstraint()
        }

        for constraint in superview.constraints {
            for bottom in [NSLayoutConstraint.Attribute.bottom, NSLayoutConstraint.Attribute.bottomMargin] {
                if constraint.firstAttribute == bottom && constraint.isActive && view == constraint.secondItem as? UIView {
                    return constraint
                }

                if constraint.secondAttribute == bottom && constraint.isActive && view == constraint.firstItem as? UIView {
                    return constraint
                }
            }
        }

        return NSLayoutConstraint()
    }

如何更新swift Layout Anchors？

4 个答案:

可能更优雅

定位单个视图

用法