Decoding JSON in Swift 4

Question

I am working through the Apple App Development Guide and this is the code I am working with right now...

struct CategoryInfo: Codable {
    var category: String
    var description: String
    var logo: String
    var mobileCategoryName: String

    enum Keys: String, CodingKey {
        case category
        case description = "descr"
        case logo
        case mobileCategoryName = "mobileCatName"
    }

    init(from decoder: Decoder) throws {
        let valueContainer = try decoder.container(keyedBy: Keys.self)
        self.category = try valueContainer.decode(String.self, forKey: Keys.category)
        self.description = try valueContainer.decode(String.self, forKey: Keys.description)
        self.logo = try valueContainer.decode(String.self, forKey: Keys.logo)
        self.mobileCategoryName = try valueContainer.decode(String.self, forKey: Keys.mobileCategoryName)
    }
}

override func viewDidLoad() {
    super.viewDidLoad()
    let categories = Industry_TableViewController()
    categories.fetchCategoryInfo { (category) in
        if let category = category {
            print(category)
        }
    }
}

func fetchCategoryInfo(completion: @escaping(CategoryInfo?) -> Void) {
    let url = URL(string: "XXXXX")!        
    let task = URLSession.shared.dataTask(with: url) {
        (data, response, error) in
        let jsonDecoder = JSONDecoder()
        if let data = data,
            let category = try? jsonDecoder.decode(CategoryInfo.self, from: data) {
                completion(category)
            } else {
                print("Nothing reutrned or Not decoded")
                completion(nil)
            }
    }
    task.resume()
}

it works fine when my returned JSON is in the following format...

{"category":"Excavators","descr":"Compact, Mid-Sized, Large, Wheeled, Tracked...","logo":"excavators","mobileCatName":"Excavators"}

My struct is created and all the variables are populated correctly. But the API doesn't bring back one category at a time it brings back multiple like so...

[{"category":"Aerial Lifts","descr":"Aerial Lifts, Man Lifts, Scissor Lifts...","logo":"aeriallifts","mobileCatName":"Aerial Lifts"},{"category":"Aggregate Equipment","descr":"Crushing, Screening, Conveyors, Feeders and Stackers...","logo":"aggregateequipment","mobileCatName":"Aggregate"},{"category":"Agricultural Equipment","descr":"Tractors, Harvesters, Combines, Tillers...","logo":"agricultural","mobileCatName":"Agricultural"}]

And I am running into a wall trying to figure out how to get this decoded properly. I've gone down so many routes I don't even know what to search for any more. Can anyone help or point me in a direction.

Answer 1

You need to modify your function to parse an array of categories instead of a single one. You just need to pass the Array<CategoryInfo> metatype to the decode function and modify the function signature such that the completion handler also returns an array.

func fetchCategoryInfo(completion: @escaping ([CategoryInfo]?) -> Void) {
    let url = URL(string: "XXXXX")!        
    let task = URLSession.shared.dataTask(with: url) {
        (data, response, error) in
        let jsonDecoder = JSONDecoder()
        if let data = data,
            let categories = try? jsonDecoder.decode([CategoryInfo].self, from: data) {
                completion(categories)
            } else {
                print("Nothing reutrned or Not decoded")
                completion(nil)
            }
    }
    task.resume()
}

Answer 2

try? jsonDecoder.decode([CategoryInfo].self, from: data)