JSON Parsing Help in Swift 4 - Data Structure Issue? - ios

Question

New on here and to Swift so please go easy on me..
Am a bit stuck when trying to parse JSON which contains nested dictionaries. I imagine its something wrong with the data strutures I have created and I have tryed everthing to rectify but still getting the same issue.
This is the JSON api I am trying to work with:
https://api.coindesk.com/v1/bpi/currentprice.json
These are the data structures I have created to model this:
struct base: Decodable {
let disclaimer: String
let bpi: [Bpi]
}
struct Bpi: Decodable {
let USD: [USD]
}
struct USD: Decodable {
let rate_float: Float
}
And here is my code in the VC :
override func viewDidLoad() {
super.viewDidLoad()
let jsonURLString = "https://api.coindesk.com/v1/bpi/currentprice.json"
guard let url = URL(string: jsonURLString) else {return}
URLSession.shared.dataTask(with: url) { (data, response, err) in
guard let data = data else {return}
do {
let bitcoinData = try JSONDecoder().decode(base.self, from: data)
print(bitcoinData.bpi)
} catch {
print("error")
}
} .resume() // Fires off the session
}
I can grab the data from the disclaimer string or the other strings in the root dictionary but that is it. I cannot parse anything further with the nested dictonaries - it just throws back the catch error.
Here is the JSON:
{
"time": {
"updated": "Nov 2, 2017 06:08:00 UTC",
"updatedISO": "2017-11-02T06:08:00+00:00",
"updateduk": "Nov 2, 2017 at 06:08 GMT"
},
"disclaimer": "This data was produced from the CoinDesk Bitcoin Price Index (USD). Non-USD currency data converted using hourly conversion rate from openexchangerates.org",
"chartName": "Bitcoin",
"bpi": {
"USD": {
"code": "USD",
"symbol": "$",
"rate": "6,889.4013",
"description": "United States Dollar",
"rate_float": 6889.4013
},
"GBP": {
"code": "GBP",
"symbol": "£",
"rate": "5,184.4053",
"description": "British Pound Sterling",
"rate_float": 5184.4053
},
"EUR": {
"code": "EUR",
"symbol": "€",
"rate": "5,910.4587",
"description": "Euro",
"rate_float": 5910.4587
}
}
}
Is there something I am clearly doing wrong here?
Thanks for the help in advance and sorry if my formatting sucks!

Answer 1

Try following model, with this it works - both bpi and USD are not arrays, just single values:
struct base: Decodable {
let disclaimer: String
let bpi: Bpi
}
struct Bpi: Decodable {
let USD: USD
}
struct USD: Decodable {
let rate_float: Float
}

Answer 2

Dictionaries (Dictionary<K,V>) are implicitly Decodable compliant if both generic types K and V are decodable.
Assuming you create a struct Coin for the currencies
struct Coin: Decodable {
private enum CodingKeys : String, CodingKey {
case code, symbol, rate, description, rateFloat = "rate_float"
}
let code : String
let symbol : String
let rate : String
let description : String
let rateFloat : Float
}
you can easily decode the currency dictionaries as [String:Coin] without any additional code
struct Base: Decodable {
private enum CodingKeys : String, CodingKey {
case disclaimer, coins = "bpi"
}
let disclaimer: String
let coins: [String:Coin]
}
And use it
let bitcoinData = try JSONDecoder().decode(Base.self, from: data)
print(bitcoinData.coins)
Alternatively if you want the currencies as an array of Coin you can write a custom initializer and map the dictionary values to an array.
This example decodes also the updatedISO value in the time dictionary
struct Base: Decodable {
struct Time : Decodable {
private enum CodingKeys : String, CodingKey {
case updated = "updatedISO"
}
let updated : Date
}
private enum CodingKeys : String, CodingKey {
case disclaimer, bpi, time
}
let disclaimer: String
let coins: [Coin]
let updated : Date
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
disclaimer = try container.decode(String.self, forKey: .disclaimer)
let bpi = try container.decode([String:Coin].self, forKey: .bpi)
coins = Array(bpi.values.sorted(by: {$0.code < $1.code}))
let time = try container.decode(Time.self, forKey: .time)
updated = time.updated
}
}
And use this example
let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .iso8601
let bitcoinData = try decoder.decode(Base.self, from: data)
print(bitcoinData.coins)

Answer 3

You declared your bpi & use properties as arrays but they were dictionaries (nested json objects). If you have sample JSON you can try this converter next time: https://danieltmbr.github.io/JsonCodeGenerator/
It generates the following output:
struct Root: Codable {
let time: Time
let disclaimer: String
let chartName: String
let bpi: Bpi
}
struct Time: Codable {
let updated: String
let updatedISO: String
let updateduk: String
}
struct Bpi: Codable {
let USD: USD
let GBP: USD
let EUR: USD
}
struct USD: Codable {
let code: String
let symbol: String
let rate: String
let description: String
let rateFloat: Double
private enum CodingKeys: String, CodingKey {
case code
case symbol
case rate
case description
case rateFloat = "rate_float"
}
}