如何将关联对象与枚举一起使用？

Question

我有一个 ViewController，我使用关联对象向其中添加了两个新属性：一个枚举和一个字符串（字符串版本取自 here）

这是我的示例代码：

extension UIViewController {

    private struct AssociatedKeys {
        static var handle = "handle"
    }

    enum CustomStringEnum: String {
        case One = "One"
        case Two = "Two"
        case Three = "Three"
    }

    var customEnum: CustomStringEnum {
        get {
            return objc_getAssociatedObject(self, &AssociatedKeys.handle) as? CustomStringEnum ?? .One
        }
        set {
            objc_setAssociatedObject(self, &AssociatedKeys.handle, newValue.rawValue, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN_NONATOMIC)
        }
    }

    var descriptiveName: String {
        get {
            return objc_getAssociatedObject(self, &AssociatedKeys.handle) as! String
        }

        set {
            objc_setAssociatedObject(
                self,
                &AssociatedKeys.handle,
                newValue as NSString?,
                .OBJC_ASSOCIATION_RETAIN_NONATOMIC
            )
        }
    }
}

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        let vc = UIViewController()
        vc.customEnum = .Three
        vc.descriptiveName = "Three"

        print(vc.customEnum.rawValue) // -> This prints "One"
        print(vc.descriptiveName)     // -> This prints "Three"
    }
}

字符串版本可以正常工作，但枚举版本不能。而且我不确定问题出在哪里。

objc_getAssociatedObject 或 objc_setAssociatedObject 有问题。 get版本好像一直都是nil，所以返回默认值One。

Answer 1

您在 get 函数中硬编码了 .One。

根据您的评论，您对相关值的复杂化没有任何意义，您应该简化：

enum Numbers: String {
    case One = "One"
    case Two = "Two"
    case Three = "Three"

    // default
    init() { self = .One }

    static let germanNumbers = [One: "Eins", Two: "Zwei", Three: "Drei"]
    var germanString: String { return Numbers.germanNumbers[self]! }
}

let num = Numbers.Three

print(num)              // "Three"
print(num.rawValue)     // "Three"

let defaultNum = Numbers()
print(defaultNum)       // "One"

print(num.germanString)        // "Drei"
print(defaultNum.germanString) // "Eins"

Answer 2

将您的代码更改为此

extension UIViewController {

private struct AssociatedKeys {
    static var handle = "handle"
    static var enumContext = "enumContext"
}

enum CustomStringEnum: String {
    case One = "One"
    case Two = "Two"
    case Three = "Three"
}

var customEnum: CustomStringEnum {
    get {
        let rawvalue = objc_getAssociatedObject(self, &AssociatedKeys.enumContext)
        if rawvalue == nil{
            return .One
        }else{
            return CustomStringEnum(rawValue: rawvalue as! String)!;
        }
    }
    set {
        objc_setAssociatedObject(self, &AssociatedKeys.enumContext, newValue.rawValue, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN_NONATOMIC)
    }
}

var descriptiveName: String {
    get {
        return objc_getAssociatedObject(self, &AssociatedKeys.handle) as! String
    }

    set {
        objc_setAssociatedObject(
            self,
            &AssociatedKeys.handle,
            newValue as NSString?,
            .OBJC_ASSOCIATION_RETAIN_NONATOMIC
        )
    }
}
}

然后就可以了

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