Consuming JSON in Swift

JSON is a fundamental internet format and if you are building iOS apps the chance you need to download and consume JSON files is extremely high. Additionally, with the introduction of the statically typed Swift language it's been a little more difficult to work with JSON properly. This talk will cover what JSON is, how one can work with it naturally in Swift, the limitations of doing so, a review of a few popular third party solutions and the introduction of a new JSON tool about to be open sourced by Big Nerd Ranch.

Video: https://vimeo.com/152112429
Code: https://github.com/zorn/JSONFunHouse

Transcript

1. Consuming JSON in Swift
   Mike Zornek • January 14, 2016
   

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4. Consuming JSON in Swift
   

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5. What is JSON?
   

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6. [
   {
   "title": "April Main Meeting",
   "date": "2016-04-14T18:30:00-0500",
   "rsvp_count": 2,
   "announced": false
   },
   {
   "title": "February Main Meeting",
   "date": "2016-02-11T18:30:00-0500",
   "rsvp_count": 31,
   "announced": true
   },
   {
   "title": "March Main Meeting",
   "date": null,
   "rsvp_count": 4,
   "announced": false
   }
   ]
   

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7. Consuming JSON in Swift
   Why do this talk?
   

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9. https://github.com/zorn/JSONFunHouse
   

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10. Native Swift
    

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11. {
    "latitude": 39.9550363,
    "longitude": -75.167381,
    "timezone": "America/New_York",
    "offset": -5,
    "currently": {
    "time": 1452470553,
    "summary": "Clear",
    "icon": "clear-night",
    "nearestStormDistance": 24,
    "nearestStormBearing": 78,
    "precipIntensity": 0,
    "precipProbability": 0,
    "temperature": 46.8,
    ...
    },
    ...
    ]
    https://developer.forecast.io/
    

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13. import UIKit
    import Freddy
    class WeatherViewController: UIViewController {
    @IBOutlet var temperatureLabel: UILabel!
    @IBOutlet var summaryLabel: UILabel!
    var temperature: Double = -99.9
    var summary = "Unknown"
    override func viewDidLoad() {
    super.viewDidLoad()
    loadWeather()
    }
    override func viewWillAppear(animated: Bool) {
    super.viewWillAppear(animated)
    temperatureLabel.text = String(format:"%.1f°", temperature)
    summaryLabel.text = summary
    }
    func loadWeather() {
    fatalError("loadWeather() should be implemented by a subclass")
    }
    }
    

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14. override func loadWeather() {
    if let data = getDataFromLocalJSONFileWithName("weather") {
    } else {
    presentError("Could not load data file.")
    }
    }
    

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15. override func loadWeather() {
    if let data = getDataFromLocalJSONFileWithName("weather") {
    do {
    if let weatherDictionary = try NSJSONSerialization.JSONObjectWithData(data,
    options: []) as? [String: AnyObject] {
    } else {
    presentError("Could not decode JSON data.")
    }
    } catch {
    presentError(error)
    }
    } else {
    presentError("Could not load data file.")
    }
    }
    

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16. override func loadWeather() {
    if let data = getDataFromLocalJSONFileWithName("weather") {
    do {
    if let weatherDictionary = try NSJSONSerialization.JSONObjectWithData(data,
    options: []) as? [String: AnyObject] {
    if let currentlyDictionary = weatherDictionary["currently"] as? [String: AnyObject] {
    } else {
    presentError("Could not find `currently` key")
    }
    } else {
    presentError("Could not decode JSON data.")
    }
    } catch {
    presentError(error)
    }
    } else {
    presentError("Could not load data file.")
    }
    }
    

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17. override func loadWeather() {
    if let data = getDataFromLocalJSONFileWithName("weather") {
    do {
    if let weatherDictionary = try NSJSONSerialization.JSONObjectWithData(data, options: []) as? [String: AnyObject] {
    if let currentlyDictionary = weatherDictionary["currently"] as? [String: AnyObject] {
    if let temperature = currentlyDictionary["temperature"] as? Double {
    if let summary = currentlyDictionary["summary"] as? String {
    self.temperature = temperature
    self.summary = summary
    } else {
    presentError("Could not find `summary` key")
    }
    } else {
    presentError("Could not find `temperature` key")
    }
    } else {
    presentError("Could not find `currently` key")
    }
    } else {
    presentError("Cound not decode JSON data.")
    }
    } catch {
    presentError(error)
    }
    } else {
    presentError("Could not load data file.")
    }
    }
    

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18. override func loadWeather() {
    if let data = getDataFromLocalJSONFileWithName("weather") {
    do {
    if let weatherDictionary = try NSJSONSerialization.JSONObjectWithData(data, options: []) as? [String: AnyObject],
    let currentlyDictionary = weatherDictionary["currently"] as? [String: AnyObject],
    let temperature = currentlyDictionary["temperature"] as? Double,
    let summary = currentlyDictionary["summary"] as? String {
    self.temperature = temperature
    self.summary = summary
    } else {
    presentError("Could not parse JSON.")
    }
    } catch {
    presentError(error)
    }
    } else {
    presentError("Could not load data file.")
    }
    }
    

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19. Freddy
    A reusable framework for parsing JSON in Swift.
    

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20. Design Goals
    1. A type safe solution to parsing JSON in Swift.
    2. An idiomatic solution that takes advantage of Swift’s features.
    3. Great error information for mistakes that commonly occur while
    parsing JSON.
    4. Speed.
    

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21. override func loadWeather() {
    if let data = getDataFromLocalJSONFileWithName("weather") {
    } else {
    presentError("Could not load data file.")
    }
    }
    

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22. override func loadWeather() {
    if let data = getDataFromLocalJSONFileWithName("weather") {
    do {
    } catch {
    presentError(error)
    }
    } else {
    presentError("Could not load data file.")
    }
    }
    

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23. override func loadWeather() {
    if let data = getDataFromLocalJSONFileWithName("weather") {
    do {
    let json = try JSON(data: data)
    } catch {
    presentError(error)
    }
    } else {
    presentError("Could not load data file.")
    }
    }
    

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24. override func loadWeather() {
    if let data = getDataFromLocalJSONFileWithName("weather") {
    do {
    let json = try JSON(data: data)
    temperature = try json.double("currently", "temperature")
    summary = try json.string("currently", "summary")
    } catch {
    presentError(error)
    }
    } else {
    presentError("Could not load data file.")
    }
    }
    

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25. [
    {
    "character": "Malcolm \"Mal\" Reynolds",
    "bio": "The owner of Serenity and former Independent sergeant in the pivotal Battle of
    Serenity Valley. Malcolm grew up on a ranch, and was raised by his mother and the ranch
    hands. In the Unification War, he fought for the Independent Army, the \"Browncoats\", as a
    platoon sergeant in the 57th Overlanders. He is cunning, a capable leader and a skilled
    fighter. Mal's main character drive is his will for independence. While he is not above
    petty theft, smuggling or even killing to maintain his free lifestyle, he is generally
    honest in his dealings with others, fiercely loyal to his crew and closely follows a
    personal moral code."
    },
    {
    "character": "Zoe Alleyne Washburne",
    "bio": "Second-in-command onboard Serenity, a loyal wartime friend of Captain Reynolds,
    and the wife of Wash. Her surname during the Unification War was Alleyne. She was born and
    raised on a ship and served under Mal during the war as a corporal. Described by her husband
    as a \"warrior woman\", she is a capable fighter who keeps calm even in the most dangerous
    situations. She demonstrates an almost unconditional loyalty to Mal, the only exception
    noted being her marriage to Wash, which the captain claims was against his orders."
    },
    ...
    ]
    

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26. import Foundation
    struct FireflyCastMember {
    let name: String
    let biography: String
    init(name: String, biography: String) {
    self.name = name
    self.biography = biography
    }
    }
    

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27. import Foundation
    struct FireflyCastMember {
    let name: String
    let biography: String
    init(name: String, biography: String) {
    self.name = name
    self.biography = biography
    }
    }
    extension FireflyCastMember: JSONDecodable {
    init(json value: JSON) throws {
    name = try value.string("character")
    biography = try value.string("bio")
    }
    }
    

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28. private func loadCastData() {
    if let data = getDataFromFileURL(self.dataURL) {
    do {
    let json = try JSON(data: data)
    self.castList = try json.array().map(FireflyCastMember.init)
    } catch {
    presentError(error)
    }
    } else {
    presentError("Could not load data file.")
    }
    }
    

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29. [
    {
    "title": "April Main Meeting",
    "date": "2016-04-14T18:30:00-0500",
    "rsvp_count": 2,
    "announced": false
    },
    {
    "title": "February Main Meeting",
    "date": "2016-02-11T18:30:00-0500",
    "rsvp_count": 31,
    "announced": true
    },
    {
    "title": "March Main Meeting",
    "date": null,
    "rsvp_count": 4,
    "announced": false
    }
    ]
    

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30. struct Meeting {
    let title: String
    let date: NSDate
    let rsvpCount: Int
    init(title: String, date: NSDate, rsvpCount: Int) {
    self.title = title
    self.date = date
    self.rsvpCount = rsvpCount
    }
    }
    

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31. struct Meeting {
    enum Error: ErrorType {
    case DateParseErrorFromString(String)
    }
    ...
    }
    extension Meeting: JSONDecodable {
    init(json value: JSON) throws {
    title = try value.string("title")
    rsvpCount = try value.int("rsvp_count")
    let dateString = try value.string("date")
    let df = NSDateFormatter()
    // 2016-03-10T18:30:00-0500
    df.dateFormat = "yyyy-MM-dd'T'HH:mm:ssZZZZ"
    if let parsedDate = df.dateFromString(dateString) {
    date = parsedDate
    } else {
    throw Error.DateParseErrorFromString(dateString)
    }
    }
    }
    

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32. JSONFunHouse Demo
    

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33. Native SwiftyJSON Argo Freddy
    Type Safe
    Idiomatic
    Error
    Handling
    Speed
    

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34. Native SwiftyJSON Argo Freddy
    Type Safe D
    Idiomatic D
    Error
    Handling
    D
    Speed C
    

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35. Native SwiftyJSON Argo Freddy
    Type Safe D B
    Idiomatic D B
    Error
    Handling
    D C
    Speed C C
    

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36. Native SwiftyJSON Argo Freddy
    Type Safe D B B
    Idiomatic D B D
    Error
    Handling
    D C B
    Speed C C C
    

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37. Native SwiftyJSON Argo Freddy
    Type Safe D B B A
    Idiomatic D B D A
    Error
    Handling
    D C B A
    Speed C C C A
    

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39. More JSON Thoughts
    • Freddy does have a new JSONEncodable protocol.
    • Build Services that are powered with DataSources.
    • See: Code Patterns https://vimeo.com/124773343
    • Don’t be afraid to make download representations.
    • JSONAPI.org
    • Swagger
    

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40. https://github.com/zorn/JSONFunHouse
    Please clone it and try it out. Feedback very welcome.
    Mike Zornek
    @zorn
    zorn@bignerdranch.com
    Keep an eye out for the official release of Freddy soon™.
    BNR’s Core Data Stack
    https://www.bignerdranch.com
    /blog/introducing-the-big-nerd-ranch-core-data-stack/
    

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