在 swift 中构造 JSON

Question

我正在尝试使用 Swift 构建以下 JSON，因为这在我使用 Postman 进行测试时有效。我需要能够更改参数的值，所以我尽量避免只构建一个字符串：

{
   "item": {
      "record": "10",
      "field_name": "orientation_forward",
      "redcap_repeat_instance": "1",
      "redcap_repeat_instrument": "range_of_motion_result",
      "value": "4",
      "redcap_event_name": []
   }
}

这是我的尝试，但当我测试它时，它甚至似乎不是有效的 JSON：

var record = "10"
var field_name = "orientation_forward"
var repeat_instance = "1"
var repeat_instrument = "range_of_motion_result"
var value = "4"
var event: [String] = [] // not sure how else to pass in '[]' when empty

    let dataObject: [String: Any] = [
        "item":
            ["record": record,
             "field_name": field_name,
             "redcap_repeat_instance": repeat_instance,
             "redcap_repeat_instrument": repeat_instrument,
             "value": value,
             "redcap_event_name": event]
    ]
            
    if let jsonData = try? JSONSerialization.data(withJSONObject: dataObject, options: .init(rawValue: 0)) as? Data
    {
        // Check if it worked...
        print(String(data: jsonData!, encoding: .utf8)!)
        let jsonTest = JSONSerialization.isValidJSONObject(jsonData) // false!
        print(jsonTest)

    }

所有帮助都慷慨地接受了。提前致谢。

Answer 1

最好的方法是在这里使用Codable，开始时需要做更多的工作，但最终代码会更简洁。

所以首先我们创建一个符合Codable的结构体

struct Item: Codable {
    let record: String
    let fieldName: String
    let repeatInstance: String
    let repeatInstrument: String
    let value: String
    let event: [String]

    enum CodingKeys: String, CodingKey {
        case record
        case fieldName = "field_name"
        case repeatInstance = "redcap_repeat_instance"
        case repeatInstrument = "redcap_repeat_instrument"
        case value
        case event = "redcap_event_name"
    }
}

CodingKeys 枚举用于获取正确的字段名称

然后就这样使用

let item = Item(record: "10", fieldName: "orientation_forward", repeatInstance: "1", repeatInstrument: "range_of_motion_result", value: "4", event: [])

do {
    let data = try JSONEncoder().encode(["item": item])
    
    if let s = String(data: data, encoding: .utf8) { print(s) }
} catch {
    print(error)
}

{"item":{"field_name":"orientation_forward","value":"4","re​​dcap_event_name":[],"redcap_repeat_instrument":"range_of_motion_result","re​​cord":"10","re​​dcap_repeat_instance ":"1"}}

有些人更喜欢一直使用自定义类型，如果是这样，您可以创建顶级结构而不是使用字典

struct ItemContainer: Codable {
    let item: Item
}

然后编码会变成类似

let data = try JSONEncoder().encode(ItemContainer(item: item))

但最终结果是一样的