How can I rewrite this function so that it uses SwiftyJSON instead of JSON.swift?

Question

I'm looking at the Ray Wenderlich tutorial http://www.raywenderlich.com/90971/introduction-mapkit-swift-tutorial and he is using there this function:

class func fromJSON(json: [JSONValue]) -> Artwork? {
  // 1
  var title: String
  if let titleOrNil = json[16].string {
    title = titleOrNil
  } else {
    title = ""
  }
  let locationName = json[12].string
  let discipline = json[15].string

  // 2
  let latitude = (json[18].string! as NSString).doubleValue
  let longitude = (json[19].string! as NSString).doubleValue
  let coordinate = CLLocationCoordinate2D(latitude: latitude, longitude: longitude)

  // 3
  return Artwork(title: title, locationName: locationName!, discipline: discipline!, coordinate: coordinate)
}

Since I'm using SwiftyJSON in my project I would like to stay with that, so I thought about rewriting this function based on that.

If I understand correctly, this function takes one json node and creates Artwork object from it.

So how can I refer to a single json node with SwiftyJSON?

I tried doing:

class func fromJSON(JSON_: (data: dataFromNetworking))->Artwork?{

}

but it causes error use of undeclared type dataFromNetworking. On the other hand that's exactly how they use it in the documentation https://github.com/SwiftyJSON/SwiftyJSON

Could you help me with rewriting it?

Quintile

Answer 1

My suggestion: separate the model layer from the presentation layer.

ArtworkModel

First of all you need a way to represent the data. A struct is perfect for this.

struct ArtworkModel {
    let title: String
    let locationName: String
    let discipline: String
    let coordinate: CLLocationCoordinate2D

    init?(json:JSON) {
        guard let
            locationName = json[12].string,
            discipline = json[15].string,
            latitudeString = json[18].string,
            latitude = Double(latitudeString),
            longitueString = json[19].string,
            longitude = Double(longitueString) else { return nil }
        self.title = json[16].string ?? ""
        self.locationName = locationName
        self.discipline = discipline
        self.coordinate = CLLocationCoordinate2D(latitude: latitude, longitude: longitude)
    }
}

As you can see ArtworkModel is capable to initialize itself from a json.

The presentation layer

Now the Artwork (conform to MKAnnotation) becomes much easier.

class Artwork: NSObject, MKAnnotation {
    private let artworkModel: ArtworkModel

    init(artworkModel: ArtworkModel) {
        self.artworkModel = artworkModel
        super.init()
    }

    var title: String? { return artworkModel.title }
    var subtitle: String? { return artworkModel.locationName }
    var coordinate: CLLocationCoordinate2D { return artworkModel.coordinate }
}

Usage

You function now becomes

class func fromJSON(json: JSON) -> Artwork? {
    guard let model = ArtworkModel(json: json) else { return nil }
    return Artwork(artworkModel: model)
}

Agon

Again, the artwork data source is a json text file in the application bundle. It's guaranteed that all parameters of the artwork items are valid and non-optional. The guard expression will never ever fail. – Postaxial

Hi @vadian: yes it's the exact same scenario we already examined a few days ago. I see your point of view but I still prefer the paranoid approach. Specifically now since data comes from the network. – Agon

Answer 2

To use SwiftyJSON in this project first you have to change the method to retrieve the data from the property list file.

Note: This replacement is for Swift 2.

Replace the method loadInitialData() in ViewController with

  func loadInitialData() {

    do {
      let fileName = NSBundle.mainBundle().pathForResource("PublicArt", ofType: "json")
      let data = try NSData(contentsOfFile: fileName!, options: NSDataReadingOptions())

      let jsonObject = JSON(data:data)
      if let jsonData = jsonObject["data"].array {
        for artworkJSON in jsonData {
          if let artworkJSONArray = artworkJSON.array, artwork = Artwork.fromJSON(artworkJSONArray) {
            artworks.append(artwork)
          }
        }
      }
    } catch let error as NSError {
      print(error)
    }
  }

And then just exchange [JSONValue] in the method

class func fromJSON(json: [JSONValue]) -> Artwork? {

of the Artworkclass with [JSON], so it's now

class func fromJSON(json: [JSON]) -> Artwork? {

That's it.

Postaxial