Decoding a JSON without keys in Swift 4

Question

I'm using an API that returns this pretty horrible JSON:

[   "A string",   [     "A string",     "A string",     "A string",     "A string",     …   ] ] 

I'm trying to decode the nested array using JSONDecoder, but it doesn't have a single key and I really don't know where to start… Do you have any idea?

Thanks a lot!

Answer 1

If the structure stays the same, you can use this Decodable approach.

First create a decodable Model like this:

struct MyModel: Decodable {     let firstString: String     let stringArray: [String]      init(from decoder: Decoder) throws {         var container = try decoder.unkeyedContainer()         firstString = try container.decode(String.self)         stringArray = try container.decode([String].self)     } } 

Or if you really want to keep the JSON's structure, like this:

struct MyModel: Decodable {     let array: [Any]      init(from decoder: Decoder) throws {         var container = try decoder.unkeyedContainer()         let firstString = try container.decode(String.self)         let stringArray = try container.decode([String].self)         array = [firstString, stringArray]     } } 

And use it like this

let jsonString = """ ["A string1", ["A string2", "A string3", "A string4", "A string5"]] """ if let jsonData = jsonString.data(using: .utf8) {     let myModel = try? JSONDecoder().decode(MyModel.self, from: jsonData) } 

Answer 2

This is a bit interesting for decoding.

You don't have any key. So it eliminates the need of a wrapper struct.

But look at the inner types. You get mixture of String and [String] types. So you need something that deals with this mixture type. You would need an enum to be precise.

// I've provided the Encodable & Decodable both with Codable for clarity. You obviously can omit the implementation for Encodable enum StringOrArrayType: Codable {     case string(String)     case array([String])      init(from decoder: Decoder) throws {         let container = try decoder.singleValueContainer()         do {             self = try .string(container.decode(String.self))         } catch DecodingError.typeMismatch {             do {                 self = try .array(container.decode([String].self))             } catch DecodingError.typeMismatch {                 throw DecodingError.typeMismatch(StringOrArrayType.self, DecodingError.Context(codingPath: decoder.codingPath, debugDescription: "Encoded payload conflicts with expected type"))             }         }     }      func encode(to encoder: Encoder) throws {         var container = encoder.singleValueContainer()         switch self {         case .string(let string):             try container.encode(string)         case .array(let array):             try container.encode(array)         }     } } 

Decoding Process:

let json = """ [   "A string",   [     "A string",     "A string",     "A string",     "A string"   ] ] """.data(using: .utf8)!  do {     let response = try JSONDecoder().decode([StringOrArrayType].self, from: json)     // Here, you have your Array     print(response) // ["A string", ["A string", "A string", "A string", "A string"]]      // If you want to get elements from this Array, you might do something like below     response.forEach({ (element) in         if case .string(let string) = element {             print(string) // "A string"         }         if case .array(let array) = element {             print(array) // ["A string", "A string", "A string", "A string"]         }     }) } catch {     print(error) }