Contents.swift

//: [Previous Topic](@previous)
/*:
 # Playground for Presenting
 # Customize `CodingKey`
 */
import Foundation

//: ### Decoding From JSON string to Message Object which contain a from Person object
//: ### and customize `CodingKeys`
//:1. Create A simple json `Data` from `JSON` String
/*:
 A Message JSON Object
 ```
 {
     "message": "Hi, How are you?",
     "create": 1523895892938,
     "from": {
                 "name" : "Ali",
                 "age":25,
                 "email":"ali@gmail.com",
                 "address":"Iran, Tehran"
             }
 }
 ```
 */
let jsonData = """
{
     "message": "Hi, How are you?",
     "create": 1523895892938,
     "from": {
                 "name" : "Ali",
                 "age":25,
                 "email":"ali@gmail.com",
                 "address":"Iran, Tehran"
             }
 }
""".data(using: .utf8)!

//:2. Define a struct and called Message which adapt to `Codable` Protocol
struct Message : Codable {
    
    let message : String
    let create : TimeInterval
    let sender : Person
    
/*:
3. Declared CodingKeys\
     which is `enum` of `String` and adapt to `CodingKey` protocol\
     [CodingKey Apple Document](https://developer.apple.com/documentation/swift/codingkey)
 */
    private enum CodingKeys : String, CodingKey {
//: * message represent of *message* property
        case message
//: * create represent of *create* property
        case create
/*:
* sender represent of *sender* property but\
     we need to set value of *sender* case to "from"\
     **Note:**"from" is json key that present in message json string
  */
        case sender = "from"
    }
    
//:4. Define a nested struct and named Person which adapted to `Codable` Protocol
    struct Person : Codable {
        let name : String
        let age : Int
        let email : String
        let address : String
        
/*:
**Note:** CodingKeys of `Person` struct will be generated by compiler\
        so we dont need to customize *CodingKeys*
 
        private enum CodingKeys : String, CodingKey {
            case name
            case age
            case email
            case address
        }
 */
    }
}

//:5. defind jsonDecoder as JSONDecoder
let jsonDecoder = JSONDecoder()

do {
/*:
 6. we use `-decode` method to decode `jsonData` into `Message` object with `try` option
 - first parameter is type of Object which want convert into such as `Int`, `String`,
 or Declared `struct` or `class`. The example is `Int.self`
 - second parameter is `jsonData' which we want convert from it into our definded type
 */
    let message = try jsonDecoder.decode(Message.self,from:jsonData)
    
//:7. print Decoded `Message` Object
    print("""
        message = \(message.message)
        create = \(message.create)
        sender  = \(message.sender)
        \n
        """)
} catch {
/*:
 8. Handling Error
 * error occured while decoding json to message swift struct
 */
    print("Error on decoding \(error)")
}
//: [Next Topic](@next)