【Swift】JSONデータをデコードする方法！JSONDecoderクラスの使い方

{
  "person": [
    {
        "name": "Ame Tsubaki",
        "age": 18,
        "hobby": ["旅行", "料理", { "web制作": ["HTML", "CSS", "php"] }]
    },
    {
        "name": "Yoshida Takashi",
        "age": 21,
        "hobby": ["読書", "ランニング", "テニス"]
    }
  ]
}

var jsonStr = """
{
        "name": "Ame Tsubaki",
        "age": 18,
        "hobby": "web制作"
}
"""

type(of: jsonStr) //String.Type

let jsonData = String(jsonStr).data(using: .utf8)!

type(of: jsonData) // Foundation.Data.Type

struct Person: Decodable {
  var name:String
  var age:Int
  var hobby:String
}

var jsonStr = """
{
        "name": "Ame Tsubaki",
        "age": 18,
        "hobby": "web制作"
}
"""

// JSONデータをString型→Data型に変換
let jsonData = String(jsonStr).data(using: .utf8)!

// JSONデータを構造体に準拠した形式に変換
let person = try! JSONDecoder().decode(Person.self, from: jsonData)

print(person.name) // Ame Tsubaki
print(person.hobby) // web制作

JSONDecoder().decode(Person.self, from: jsonData)

func decode<T>(T.Type, from: Data) -> T throws -> T where T : Decodable

print(person.name) // Ame Tsubaki
print(person.hobby) // web制作

var jsonStr = """
{
  "schoolName": "Webエンジニア学習部屋",
  "person": [
    {
        "name": "Ame Tsubaki",
        "age": 18,
        "hobby": "web制作"
    },
    {
        "name": "Yoshida Takashi",
        "age": 21,
        "hobby": "読書"
    }
  ]
}
"""

struct School: Decodable {
    var schoolName:String
    var person:[Person]
}

struct Person: Decodable {
    var name:String
    var age:Int
    var hobby:String
}

let jsonData = String(jsonStr).data(using: .utf8)!
let school = try! JSONDecoder().decode(School.self, from: jsonData)

print(school.schoolName) // Webエンジニア学習部屋
print(school.person) // [Person(name: "Ame Tsubaki", age: 18, hobby: "web制作"), Person(name: "Yoshida Takashi", age: 21, hobby: "読書")]

for people in school.person {
    print(people.name)  // Ame Tsubaki , Yoshida Takashi
}

struct School: Decodable {
    var schoolName:String
    var person:[Person]
    var address:String = ""  // JSONデータにはないプロパティを定義したい
}

Fatal error: 'try!' expression unexpectedly raised an error: debugDescription: "No value associated with key CodingKeys
// 致命的なエラー：「試してみてください！」式で予期せずエラーが発生しました：debugDescription："キーCodingKeysに関連付けられた値がありません

struct School: Decodable {
    var schoolName:String
    var person:[Person]
    var address:String = "" // 初期値を指定しないとエラーになります
    
    private enum CodingKeys: String, CodingKey {
        case schoolName, person
    }
}

{
    “snake_case”: “Test”,
    "CamelCase": 20,
}

struct MyObject: Decodable {
    let SnakeCase: String
    let CamelCase: Int

    enum CodingKeys: String, CodingKey {
        // プロパティ名 = "JSONキー名"
        case SnakeCase = "snake_case"
        case CamelCase
    }
}

{
    "key1": 1,
    "key2": 0,
}

struct AppNotify: Identifiable, Codable {
    public var id: UUID = UUID()
    public var title: String
    public var msg: String
    public var time: Date = Date()
}

let encoder = JSONEncoder()
encoder.outputFormatting = .prettyPrintedguard 
let jsonData = try? encoder.encode(notification) else { return }
guard let json = String(data: jsonData, encoding: .utf8) else { return }
print(json)

{
    "time": 741670569.590185,
    "msg": "通知メッセージ",
    "title": "通知タイトル",
    "id": "7964108A-4F26-4DD1-B421-1607AA1EA3E6"
}