如何在可编码结构中使用计算属性 (swift)

Question

我创建了一个"可编码"结构来序列化数据集并将其编码为 Json。除了计算的属性未显示在 json 字符串中外，一切正常。如何在编码阶段包含计算属性。

前任：

struct SolidObject:Codable{
    var height:Double                      = 0
    var width:Double                       = 0
    var length:Double                      = 0
    var volume:Double {
        get{
            return height * width * length
        }
    }
}
var solidObject = SolidObject()
solidObject.height = 10.2
solidObject.width = 7.3
solidObject.length = 5.0
let jsonEncoder = JSONEncoder()
do {
    let jsonData = try jsonEncoder.encode(solidObject)
    let jsonString = String(data: jsonData, encoding: .utf8)!
    print(jsonString)
} catch {
    print(error)
}

打印出"{"宽度"：7.2999999999999998，"长度"：

5，"高度"：10.1999999999999999}">

我也对拥有 7.29999.. 而不是 7.3 感到好奇，但我的主要问题是"我如何才能将"音量"也包含到这个 json 字符串中"？

Answer 1

您需要手动编码/解码，而不是让自动化的东西为您完成。这在 Swift 操场中按预期工作。

struct SolidObject: Codable {
    var height:Double                      = 0
    var width:Double                       = 0
    var length:Double                      = 0
    var volume:Double {
        get{
            return height * width * length
        }
    }
    enum CodingKeys: String, CodingKey {
        case height
        case width
        case length
        case volume
    }
    init() { }
    init(from decoder: Decoder) throws {
        let values = try decoder.container(keyedBy: CodingKeys.self)
        height = try values.decode(Double.self, forKey: .height)
        width = try values.decode(Double.self, forKey: .width)
        length = try values.decode(Double.self, forKey: .length)
    }
    func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(height, forKey: .height)
        try container.encode(width, forKey: .width)
        try container.encode(length, forKey: .length)
        try container.encode(volume, forKey: .volume)
    }
}
var solidObject = SolidObject()
solidObject.height = 10.2
solidObject.width = 7.3
solidObject.length = 5.0
let jsonEncoder = JSONEncoder()
do {
    let jsonData = try jsonEncoder.encode(solidObject)
    let jsonString = String(data: jsonData, encoding: .utf8)!
    print(jsonString)
} catch {
    print(error)
}