The document discusses JSON (JavaScript Object Notation), an open standard format used to transmit data between a server and applications. It describes how to convert JSON data to Swift types by decoding JSON into custom model objects using a JSONDecoder. It provides examples of decoding JSON into a dictionary of strings and decoding into a custom Report struct by implementing Codable and specifying coding keys. The document also discusses updating a URLSession data task completion handler to decode JSON data into a custom model object.

1. Unit 5—Lesson 5:
Working with the Web:
Decoding JSON

2. JavaScript Object Notation
JSON
{
"name": "Daren Estrada",
"favorite_movie": {
"title": "Finding Dory",
"release_year": "2016"
}
}
An open standard format that uses human readable text to transmit objects
• Each object consists of attribute-value pairs
Used primarily to transmit data between a server and applications
Language-independent data format

3. {
"name": "Daren Estrada",
"favorite_movies": [
{
"title": "Finding Dory",
"release_year": 2016
},
{
"title": "Inside Out",
"release_year": 2015
}
]
}
The basics
JSON

4. The basics
JSON
{
"name": "Daren Estrada",
"favorite_movies": [
{
"title": "Finding Dory",
"release_year": 2016
},
{
"title": "Inside Out",
"release_year": 2015
}
]
}

5. The basics
JSON
{
"name": "Daren Estrada",
"favorite_movies": [
{
"title": "Finding Dory",
"release_year": 2016
},
{
"title": "Inside Out",
"release_year": 2015
}
]
}

6. The basics
JSON
{
"name": "Daren Estrada",
"favorite_movies": [
{
"title": "Finding Dory",
"release_year": 2016
},
{
"title": "Inside Out",
"release_year": 2015
}
]
}

7. Convert JSON data to Swift types
let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
let jsonDecoder = JSONDecoder()
if let data = data,
let report = try? jsonDecoder.decode([String: String].self, from: data) {
print(report)
}
}
task.resume()

8. Decoding into custom model objects
{
"report_date": "2018-01-20",
"profile_id": "136442",
"name": "Final Results for Q4 2017",
"read_count": "5"
}

9. Decoding into custom model objects
struct Report {
let name: String
let creationDate: Date
let profileID: String
let readCount: Int?
}

10. Decoding into custom model objects
struct Report: Codable {
let name: String
let creationDate: Date
let profileID: String
let readCount: Int?
enum CodingKeys: String, CodingKey {
case name
case creationDate = "report_date"
case profileID = "profile_id"
case readCount = "read_count"
}
}

11. Decoding into custom model objects
init(from decoder: Decoder) throws {
let valueContainer = try decoder.container(keyedBy: CodingKeys.self)
self.creationDate = try valueContainer.decode(String.self,
forKey: CodingKeys.creationDate)
self.profileID = try valueContainer.decode(URL.self, forKey: CodingKeys.profileID)
self.readCount = try? valueContainer.decode(String.self, forKey: CodingKeys.readCount)
}

12. Update the request completion handler
let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
let jsonDecoder = JSONDecoder()
if let data = data,
let report = try? jsonDecoder.decode(Report.self, from: data) {
print(report)
}
}
task.resume()

13. Working with the Web: Decoding JSON
Unit 5—Lesson 6
Learn how to read and write basic JSON.
Learn how to convert JSON to and from Swift types and into your own custom model
objects.

14. Lab: iTunes Search (Part 2)
Unit 5—Lesson 4
Using the iTunes Search playground you created in the last lesson, serialize the
retrieved data into a custom model object.

15. © 2017 Apple Inc.
This work is licensed by Apple Inc. under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International license.