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

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

我正在尝试为 UIView 编写一个扩展程序，以便更轻松地为视图设置锚点。

我们的想法是编写一个这样的 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
}

可以这样调用：

 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'

我知道我可以将 topAnchor 指定为 NSLayoutYAxisAnchor 等，并将常量也作为参数提供给此方法以使其工作，但我想知道是否有办法使其与此 Anchor 结构一起使用?

解决方法

您可以使用通用。

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
        }
    }
}