swift4 - Swift 4 使用 Codable 解码 json

Question

有人能告诉我我做错了什么吗？我已经查看了这里的所有问题，例如从这里 How to decode a nested JSON struct with Swift Decodable protocol?我找到了一个看起来正是我需要的 Swift 4 Codable decoding json .

{
"success": true,
"message": "got the locations!",
"data": {
    "LocationList": [
        {
            "LocID": 1,
            "LocName": "Downtown"
        },
        {
            "LocID": 2,
            "LocName": "Uptown"
        },
        {
            "LocID": 3,
            "LocName": "Midtown"
        }
     ]
  }
}

struct Location: Codable {
    var data: [LocationList]
}

struct LocationList: Codable {
    var LocID: Int!
    var LocName: String!
}

class ViewController: UIViewController {

override func viewDidLoad() {
    super.viewDidLoad()

    let url = URL(string: "/getlocationlist")

    let task = URLSession.shared.dataTask(with: url!) { data, response, error in
        guard error == nil else {
            print(error!)
            return
        }
        guard let data = data else {
            print("Data is empty")
            return
        }

        do {
            let locList = try JSONDecoder().decode(Location.self, from: data)
            print(locList)
        } catch let error {
            print(error)
        }
    }

    task.resume()
}

我得到的错误是:

typeMismatch(Swift.Array, Swift.DecodingError.Context(codingPath: [], debugDescription: "Expected to decode Array but found a dictionary instead.", underlyingError: nil))

Answer 1

检查 JSON 文本的轮廓结构:

{
    "success": true,
    "message": "got the locations!",
    "data": {
      ...
    }
}

"data" 的值是一个 JSON 对象 {...} ，它不是一个数组。
和对象的结构:

{
    "LocationList": [
      ...
    ]
}

该对象只有一个条目 "LocationList": [...]它的值是一个数组 [...] .

您可能还需要一个结构体:

struct Location: Codable {
    var data: LocationData
}

struct LocationData: Codable {
    var LocationList: [LocationItem]
}

struct LocationItem: Codable {
    var LocID: Int!
    var LocName: String!
}

用于检测...

var jsonText = """
{
    "success": true,
    "message": "got the locations!",
    "data": {
        "LocationList": [
            {
                "LocID": 1,
                "LocName": "Downtown"
            },
            {
                "LocID": 2,
                "LocName": "Uptown"
            },
            {
                "LocID": 3,
                "LocName": "Midtown"
            }
        ]
    }
}
"""

let data = jsonText.data(using: .utf8)!
do {
    let locList = try JSONDecoder().decode(Location.self, from: data)
    print(locList)
} catch let error {
    print(error)
}