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iOS Parsing JSON Using Codable Dynamic Keys and Inheritance Dynamic Coding Keys

Posted by Jonathan Mazala
Jonathan Mazala
9,860 Points

Wondering how to solve unwrapping compiler error in swift 4

I'm seeing value of optional type 'Library.LibraryCodingKeys' not unwrapped; did you mean to use '!' or '?'?

I believe my code is the same as in the teacher's example but it's hard to tell exactly because there's no download link

1 Answer

Hao Wu
Hao Wu
12,514 Points
Hao Wu
Hao Wu
12,514 Points

Hi, I have attached my code and hope it will help you.

import Foundation

let json = """
{
  "languages": { 
    "python": {
      "designer": [
        "Guido van Rossum"
      ],
      "released": "20 February 1991"
    },
    "java": {
      "designer": [
        "James Gosling"
      ],
      "released": "May 23, 1995"
    },
    "swift": {
      "designer": [
        "Chris Lattner",
        "Apple Inc"
      ],
      "released": "June 2, 2014"
    },
    "ruby": {
      "designer": [
        "Yukihiro Matsumoto"
      ],
      "released": "1995"
    }
  }
}
""".data(using: .utf8)!

struct Language {
    let name: String
    let designer: [String]
    let releaseDate: String
}

struct Library {
    let languages: [Language]

     struct LibraryCodingKeys: CodingKey {
        let stringValue: String

        init?(stringValue: String) {
            self.stringValue = stringValue
        }

        var intValue: Int? { return nil }
        init?(intValue: Int) { return nil }

        static let languages = LibraryCodingKeys(stringValue: "languages")!
    }

    enum LanguageCodingKeys: String, CodingKey {
        case designer
        case released
    }
}

let decoder = JSONDecoder()

extension Library: Decodable {
    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: LibraryCodingKeys.self)

        let languagesContainer = try container.nestedContainer(keyedBy: LibraryCodingKeys.self, forKey: .languages)

        self.languages = try languagesContainer.allKeys.map { key in
            let languageContainer = try languagesContainer.nestedContainer(keyedBy: LanguageCodingKeys.self, forKey: key)

            let languageName = key.stringValue
            let designer = try languageContainer.decode([String].self, forKey: .designer)
            let releaseDate = try languageContainer.decode(String.self, forKey: .released)

            return Language(name: languageName, designer: designer, releaseDate: releaseDate)
        }
    }
} 

let library = try! decoder.decode(Library.self, from: json)
for language in library.languages {
    print(language.name)
}
Xavier D
Xavier D
Courses Plus Student 5,840 Points
Xavier D
Xavier D
Courses Plus Student 5,840 Points

Tanx! Proper use of indentations increases readability!

let json = """
{
    "languages":
    {
        "python":
        {
            "designer": [ "Guido van Rossum"],
            "released": "20 February 1991"
        },

        "java":
        {
            "designer": ["James Gosling"],
            "released": "May 23, 1995"
        },

        "swift":
        {
            "designer": [ "Chris Lattner", "Apple Inc"],
            "released": "June 2, 2014"
        },

        "ruby":
        {
            "designer": [ "Yukihiro Matsumoto" ],
            "released": "1995"
        }
    }
}
""".data(using: .utf8)!

XD