如何使用Swift 2.0和反射来获取属性名称及其值?

时间:2015-08-02 16:21:38

标签: reflection swift2

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() {}

}

为了获取RSS2FeedChannel实例的属性名称和值,我需要做什么?

这是我尝试的内容:

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,我尝试使用反射创建与实例匹配的Dictionary,但到目前为止,我无法获取实例的属性名称和值。

文档说:

  

可以在适当时使用可选标签,例如表示存储属性或活动枚举大小写的名称,并在字符串传递给后代方法时用于查找。

然而我只得到一些"一些"字符串。

此外,value属性返回一个类型为RSS2FeedChannel的字符串,当我希望每个孩子都是&#34;反映实例结构的元素时。&#34;!< / p>

2 个答案:

答案 0 :(得分:4)

当我理解正确时,这应解决你的问题:

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
}

swift 3的一些小变化:

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
}

答案 1 :(得分:1)

您可以使用Mirror对象上的descendent方法获取此信息。如果未找到值或选项包含任何值,它将返回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")