JSON 解码没有按预期工作 swift 4

Question

如果我想解码我的 JSON，就会发生一些奇怪的事情。

这是结构

struct chatMessages : Codable {
    var message: [chatMessage]
}

struct chatMessage : Codable {
    var user: String
    var message: String
    var status: String
    var latitude: Double
    var longitude: Double

    init(from decoder: Decoder) throws {
        let values = try decoder.container(keyedBy: CodingKeys.self)
        user = try values.decode(String.self, forKey: .user)
        message = try values.decode(String.self, forKey: .message)
        status = try values.decode(String.self, forKey: .status)
        latitude = try values.decodeIfPresent(Double.self, forKey: .latitude) ?? 0.0
        longitude = try values.decodeIfPresent(Double.self, forKey: .longitude) ?? 0.0
    }
}

这里是函数

   func loadChats() {
        print("Try to load chats...")
        do {
        let jsonData = W.getDataAsData(chatURL)
            print(jsonData)
            print(String.init(data: jsonData, encoding: .utf8)!)
            print("-----------")
            let jsonDecoder = JSONDecoder()
            let chatMessage1 = try jsonDecoder.decode(chatMessage.self, from: jsonData)
            print(chatMessage1)
        }
        catch {
            print("Something went wrong")
            print("\(error)")
        }
    }

如果返回的 JSON 是 {"user":"test","message":"Hello welcome","status":"admin","latitude":0,"longitude":0}.

返回 chatMessage(user: "test", message: "Hello welcome", status: "admin", latitude: 0.0, longitude: 0.0)

但是如果有更多消息，例如[{"user":"user1","message":"Hello welcome","status":"admin","latitude":0,"longitude":0},{"user":"user2","message":"Hello welcome","status":"admin","latitude":0,"longitude":0}] 我无法让它工作。它返回 typeMismatch(Swift.Dictionary<Swift.String, Any>, Swift.DecodingError.Context(codingPath: [], debugDescription: "Expected to decode Dictionary<String, Any> but found an array instead.", underlyingError: nil))

我试过 chatMessages.self 但没有达到预期效果。我做错了什么？

提前致谢。

Answer 1

答案很简单，你必须使用这个：

let chatMessage1 = try jsonDecoder.decode([chatMessage].self, from: jsonData)

而不是这个：

let chatMessage1 = try jsonDecoder.decode(chatMessage.self, from: jsonData)

在 loadChats() 函数中。因为你有 NSDictionary 数组。

Answer 2

您可以在 init(decoder) 内部检测并处理它，但简单的解决方案是这样做

 do {
       let chatMessage1 = try jsonDecoder.decode(chatMessage.self, from: jsonData)
   }
 catch {

    do {
        let chatMessage1 = try jsonDecoder.decode([chatMessage].self, from: jsonData)
     }
     catch {
        print(error)
      }
}

另外我认为最好将后端更改为 return 数组，即使只有一条消息

JSON 解码没有按预期工作 swift 4

JSON Decode does not work as expected swift 4

json

swift

jsondecoder