如何处理Swift中一个键的两种可能类型的解码？ [重复]

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Swift 4 JSON可解码,具有多维和多样本数组5个答案

I have a Codable struct that is used to decode incoming JSON. Unfortunately, sometimes one of its key's value is a string, and sometimes it is a float. I was able to cobble a couple of do/try/catch blocks below to get it to work, but is there a better way to handle this?

我有一个Codable结构,用于解码传入的JSON。不幸的是,有时它的一个键的值是一个字符串,有时它是一个浮点数。我能够在下面拼凑一些do / try / catch块来使它工作,但是有更好的方法来处理它吗?

struct Project: Codable {
    public let version: Float

    init(from decoder: Decoder) throws {
        var decodedVersion: Float = 1.0
        do {
            decodedVersion = try values.decode(Float.self, forKey: .version)
        } catch {
            do {
                if let inVersion = try Float(values.decode(String.self, forKey: .version)) {
                    decodedVersion = inVersion
                }
            } catch {
                throw error
            }
        }
        version = decodedVersion
    }
}

1 个解决方案

#1

If in your JSON the value associated to a key can be sometimes a Float and sometimes a String (besides fixing this error on the backend ????) you could follow this approach.

如果在您的JSON中,与键关联的值有时可能是Float,有时也是String(除了在后端修复此错误????)之外,您可以遵循此方法。

Let's say this is your "funny" JSON

让我们说这是你的“搞笑”JSON

let data = """
[
{
    "magicField": "one"
},
{
    "magicField":1
}
]
""".data(using: .utf8)!

Good, how can we elegantly represent this kind of data in Swift?

好,我们如何在Swift中优雅地表示这种数据?

struct Element:Decodable {
    let magicField: ???
}

We want magicField to always have a value, sometimes a Float and sometimes a String.

我们希望magicField总是有一个值,有时候是Float,有时候是String。

We can solve this with Quantum Mechanics... or with an Enum ????

Let's define this type

我们来定义这种类型

enum QuantumValue: Decodable {

    case float(Float), string(String)

    init(from decoder: Decoder) throws {
        if let float = try? decoder.singleValueContainer().decode(Float.self) {
            self = .float(float)
            return
        }

        if let string = try? decoder.singleValueContainer().decode(String.self) {
            self = .string(string)
            return
        }

        throw QuantumError.missingValue
    }

    enum QuantumError:Error {
        case missingValue
    }
}

As you can see a value of type QuantumValue can hold a Float or a String. Always 1 and exactly 1 value.

如您所见,QuantumValue类型的值可以包含Float或String。始终为1且正好为1。

Element

We can now define the general element of our JSON

我们现在可以定义JSON的一般元素

struct Element:Decodable {
    let magicField: QuantumValue
}

Decoding

That's it. Let's finally decode the JSON.

而已。让我们最终解码JSON。

if let elms = try? JSONDecoder().decode([Element].self, from: data) {
    print(elms)
}

Result

[
Element(magicField: QuantumValue.string("one")),
Element(magicField: QuantumValue.float(1.0))
]