无法将“NSLayoutAnchor<NSLayoutXAxisAnchor>”类型的值转换为预期的参数类型“NSLayoutAnchor<AnyObject>”

Question

我试图为UIView编写一个扩展，以便更容易地为视图设置锚点。

这样做的目的是编写一个类似于这样的setAnchors方法：

import UIKit

extension UIView {

    func setAnchors(top: Anchor? = nil,
                    bottom: Anchor? = nil,
                    leading: Anchor? = nil,
                    trailing: Anchor? = nil) {
        translatesAutoresizingMaskIntoConstraints = false
        if let top = top, let anchorType = top.type as? NSLayoutAnchor<NSLayoutYAxisAnchor>, let constant = top.constant {
            let constraint = topAnchor.constraint(equalTo: anchorType, constant: constant)
            constraint.isActive = true
        }

        if let bottom = bottom, let anchorType = bottom.type as? NSLayoutAnchor<NSLayoutYAxisAnchor>, let constant = bottom.constant {
            let constraint = bottomAnchor.constraint(equalTo: anchorType, constant: constant)
            constraint.isActive = true
        }

        if let leading = leading, let anchorType = leading.type as? NSLayoutAnchor<NSLayoutXAxisAnchor>, let constant = leading.constant {
            let constraint = leadingAnchor.constraint(equalTo: anchorType, constant: constant)
            constraint.isActive = true
        }

        if let trailing = trailing, let anchorType = trailing.type as? NSLayoutAnchor<NSLayoutXAxisAnchor>, let constant = trailing.constant {
            let constraint = trailingAnchor.constraint(equalTo: anchorType, constant: constant)
            constraint.isActive = true
        }
    }
}

struct Anchor {
    var type: NSLayoutAnchor<AnyObject>
    var constant: CGFloat? = 0.0
}

可以这样称呼：

 topView.setAnchors(top: Anchor(type: view.topAnchor), leading: Anchor(type: view.leadingAnchor), trailing: Anchor(type: view.trailingAnchor))

我收到以下错误：

无法将“NSLayoutAnchor”类型的值转换为预期的参数类型“NSLayoutAnchor”

​

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我知道我可以给topAnchor作为NSLayoutYAxisAnchor等等，并且给常量作为这个方法的参数来实现这个工作，但是我想知道是否有一种方法可以使它与这个Anchor结构一起工作？

Answer 1

你可以用通用的。

struct Anchor<T: AnyObject>{
    var type: NSLayoutAnchor<T>
    var constant: CGFloat? = 0.0
}

extension UIView {
    func setAnchors<T: AnyObject>(top: Anchor<T>? = nil,
                    bottom: Anchor<T>? = nil,
                    leading: Anchor<T>? = nil,
                    trailing: Anchor<T>? = nil) {
        translatesAutoresizingMaskIntoConstraints = false
        if let top = top, let anchorType = top.type as? NSLayoutAnchor<NSLayoutYAxisAnchor>, let constant = top.constant {
            let constraint = topAnchor.constraint(equalTo: anchorType, constant: constant)
            constraint.isActive = true
        }

        if let bottom = bottom, let anchorType = bottom.type as? NSLayoutAnchor<NSLayoutYAxisAnchor>, let constant = bottom.constant {
            let constraint = bottomAnchor.constraint(equalTo: anchorType, constant: constant)
            constraint.isActive = true
        }

        if let leading = leading, let anchorType = leading.type as? NSLayoutAnchor<NSLayoutXAxisAnchor>, let constant = leading.constant {
            let constraint = leadingAnchor.constraint(equalTo: anchorType, constant: constant)
            constraint.isActive = true
        }

        if let trailing = trailing, let anchorType = trailing.type as? NSLayoutAnchor<NSLayoutXAxisAnchor>, let constant = trailing.constant {
            let constraint = trailingAnchor.constraint(equalTo: anchorType, constant: constant)
            constraint.isActive = true
        }
    }
}