Swift：将结构转换为 JSON？

Question

我创建了一个 struct 并想将其保存为 JSON 文件。

struct Sentence {
    var sentence = ""
    var lang = ""
}

var s = Sentence()
s.sentence = "Hello world"
s.lang = "en"
print(s)

...结果是：

Sentence(sentence: "Hello world", lang: "en")

但是我怎样才能将 struct 对象转换成类似的东西：

{
    "sentence": "Hello world",
    "lang": "en"
}

Answer 1

使用 NSJSONSerialization class.

将此用于 reference，您可能需要创建一个函数，其中 returns JSON 序列化字符串。在此函数中，您可以获取所需的属性并从中创建一个 NSDictionary 并使用上面提到的 class。

像这样：

struct Sentence {
    var sentence = ""
    var lang = ""

    func toJSON() -> String? {
        let props = ["Sentence": self.sentence, "lang": lang]
        do {
            let jsonData = try NSJSONSerialization.dataWithJSONObject(props,
            options: .PrettyPrinted)
            return String(data: jsonData, encoding: NSUTF8StringEncoding)
        } catch let error {
            print("error converting to json: \(error)")
            return nil
        }
    }

}

因为您的结构只有两个属性，所以您自己构建 JSON 字符串可能更容易。

Answer 2

Swift 4 介绍了 Codable 协议，它提供了一种非常方便的方式来编码和解码自定义结构。

struct Sentence : Codable {
    let sentence : String
    let lang : String
}

let sentences = [Sentence(sentence: "Hello world", lang: "en"), 
                 Sentence(sentence: "Hallo Welt", lang: "de")]

do {
    let jsonData = try JSONEncoder().encode(sentences)
    let jsonString = String(data: jsonData, encoding: .utf8)!
    print(jsonString) // [{"sentence":"Hello world","lang":"en"},{"sentence":"Hallo Welt","lang":"de"}]
    
    // and decode it back
    let decodedSentences = try JSONDecoder().decode([Sentence].self, from: jsonData)
    print(decodedSentences)
} catch { print(error) }

Answer 3

Swift 4 支持 Encodable 协议 e.g.

struct Sentence: Encodable {
    var sentence: String?
    var lang: String?
}

let sentence = Sentence(sentence: "Hello world", lang: "en")

现在您可以使用 JSON 编码器自动将 Struct 转换为 JSON：

let jsonEncoder = JSONEncoder()
let jsonData = try jsonEncoder.encode(sentence)

打印出来：

let jsonString = String(data: jsonData, encoding: .utf8)
print(jsonString)

{
    "sentence": "Hello world",
    "lang": "en"
}

https://developer.apple.com/documentation/foundation/archives_and_serialization/encoding_and_decoding_custom_types

Answer 4

这是 JSON encoding/decoding 的一个很好的扩展和方法：

extension Encodable {
    
    func toJSONString() -> String {
        let jsonData = try! JSONEncoder().encode(self)
        return String(data: jsonData, encoding: .utf8)!
    }
    
}

func instantiate<T: Decodable>(jsonString: String) -> T? {
    return try? JSONDecoder().decode(T.self, from: jsonString.data(using: .utf8)!)
}

示例用法：

struct Sentence: Codable {
    var sentence = ""
    var lang = ""
}

let sentence = Sentence(sentence: "Hello world", lang: "en")
let jsonStr = sentence.toJSONString()
print(jsonStr)      // prints {"lang":"en","sentence":"Hello world"}

let sentenceFromJSON: Sentence? = instantiate(jsonString: jsonStr)
print(sentenceFromJSON!)    // same as original sentence

Swift：将结构转换为 JSON？

Swift: Convert struct to JSON?

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