如何在Swift中存储属性，就像在Objective-C中一样？

如何在Swift中存储属性，就像在Objective-C中一样？

关联对象API使用起来有点麻烦。您可以使用帮助程序类删除大部分样板。

public final class ObjectAssociation<T: AnyObject> {    private let policy: objc_AssociationPolicy    /// - Parameter policy: An association policy that will be used when linking objects.    public init(policy: objc_AssociationPolicy = .OBJC_ASSOCIATION_RETAIN_NONATOMIC) {        self.policy = policy    }    /// Accesses associated object.    /// - Parameter index: An object whose associated object is to be accessed.    public subscript(index: AnyObject) -> T? {        get { return objc_getAssociatedObject(index, Unmanaged.passUnretained(self).toOpaque()) as! T? }        set { objc_setAssociatedObject(index, Unmanaged.passUnretained(self).toOpaque(), newValue, policy) }    }}

前提是您可以以更易读的方式将属性“添加”到objective-c类：

extension SomeType {    private static let association = ObjectAssociation<NSObject>()    var simulatedProperty: NSObject? {        get { return SomeType.association[self] }        set { SomeType.association[self] = newValue }    }}

至于解决方案：

extension CALayer {    private static let initialPathAssociation = ObjectAssociation<CGPath>()    private static let shapeLayerAssociation = ObjectAssociation<CAShapeLayer>()    var initialPath: CGPath! {        get { return CALayer.initialPathAssociation[self] }        set { CALayer.initialPathAssociation[self] = newValue }    }    var shapeLayer: CAShapeLayer? {        get { return CALayer.shapeLayerAssociation[self] }        set { CALayer.shapeLayerAssociation[self] = newValue }    }}