如何使用 Swift 2.0 和反射获取属性名称及其值？

Question

鉴于此模型：

public class RSS2Feed {

    public var channel: RSS2FeedChannel?

    public init() {}
}

public class RSS2FeedChannel {   

    public var title: String?
    public var description: String?

    public init() {}

}

我需要做什么才能获得 RSS2FeedChannel 实例的属性名称和值？

这是我正在尝试的：

let feed = RSS2Feed()
feed.channel = RSS2FeedChannel()
feed.channel?.title = "The Channel Title"

let mirror = Mirror(reflecting: feed.channel)
mirror.children.first // ({Some "Some"}, {{Some "The Channel Title...

for (index, value) in mirror.children.enumerate() {
    index // 0
    value.label // "Some"
    value.value // RSS2FeedChannel
}

最终，我试图创建一个 Dictionary 来匹配实例，使用反射，但到目前为止我无法获取实例的属性名称和值。

文档说：

The optional label may be used when appropriate, e.g. to represent the name of a stored property or of an active enum case, and will be used for lookup when Strings are passed to the descendant method.

然而我只得到一个 "Some" 字符串。

此外，值属性返回类型为 RSS2FeedChannel 的字符串，而我希望每个子项都是 "An element of the reflected instance's structure."!

Answer 1

您可以在镜像对象上使用 descendent 方法来获取此信息。如果找不到值或可选值不包含值，它将 return nil。

let mirror = Mirror(reflecting: feed.channel)
let child1 = mirror.descendant("Some", "title") // "The Channel Title"

// or on one line
let child3 = Mirror(reflecting: feed).descendant("channel", "Some", "title")

Answer 2

当我理解正确时，这应该可以解决您的问题：

func aMethod() -> Void {
    let feed = RSS2Feed()
    feed.channel = RSS2FeedChannel()
    feed.channel?.title = "The Channel Title"
//  feed.channel?.description = "the description of your channel"

    guard  let channel = feed.channel else {
        return
    }

    let mirror = Mirror(reflecting: channel)
    for child in mirror.children {
        guard let key = child.label else {
            continue
        }
        let value = child.value

        guard let result = self.unwrap(value) else {
            continue
        }

        print("\(key): \(result)")
    }
}

private func unwrap(subject: Any) -> Any? {
    var value: Any?
    let mirrored = Mirror(reflecting:subject)
    if mirrored.displayStyle != .Optional {
        value = subject
    } else if let firstChild = mirrored.children.first {
        value = firstChild.value
    }
    return value
}

只是 swift 3 的一些小改动：

private func unwrap(_ subject: Any) -> Any? {
    var value: Any?
    let mirrored = Mirror(reflecting:subject)
    if mirrored.displayStyle != .optional {
        value = subject
    } else if let firstChild = mirrored.children.first {
        value = firstChild.value
    }
    return value
}

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如何使用 Swift 2.0 和反射获取属性名称及其值？