Array JSON decoding in swift - json

Question

I am trying to decode this json array and I got the following code to work, initially but it is a bit buggy.
the json is structured as following:
{
"prices": [
[
1595642361269,
180.62508267006177
],
[
1596642361269,
190.1
]
],
"market_caps": [
[
1595642361269,
3322122955.6677375
],
[
1596642361269,
3332122955.6677375
]
],
"total_volumes": [
[
1595642361269,
590499490.5115521
],
[
1595642361269,
590499490.5115521
]
]
}
my swift object is structured as:
struct MarketChart: Decodable {
let prices: [[Double]]
let market_caps: [[Double]]
let total_volumes: [[Double]]
}
I dont think it is optimal but as the json doesn't have keys for the timestamps and values I was a bit confused on how to structure it.
the following is my playground code:
func getJSON<T: Decodable>(urlString: String, completion: #escaping (T?) -> Void) {
guard let url = URL(string: urlString) else {
return
}
let request = URLRequest(url: url)
URLSession.shared.dataTask(with: request) { (data, response, error) in
if let error = error {
print(error.localizedDescription)
completion(nil)
return
}
guard let data = data else {
completion(nil)
return
}
let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .secondsSince1970
guard let decodedData = try? decoder.decode(T.self, from: data) else {
completion(nil)
return
}
completion(decodedData)
}.resume()
}
struct MarketChart: Decodable {
let prices: [[Double]]
let market_caps: [[Double]]
let total_volumes: [[Double]]
}
var priceArray: [Double] = []
print(priceArray)
getJSON(urlString: "https://api.coingecko.com/api/v3/coins/bitcoin-cash-sv/market_chart?vs_currency=usd&days=1") { (data: MarketChart?) in
if let data = data {
for item in data.prices {
priceArray.append(item.first!)
}
}
}
print(priceArray)
I am trying to get all the values into an array and it did work initially but now just keeps printing an empty array. my end goal is to crate a graph of the values over time in a project and I did it successfully the first time but now I keep getting an error saying it can't get the value from an empty array.
my Xcode project file is as follows:
import SwiftUI
import SwiftUICharts
import Combine
struct CoinGeckoBSVMarketChart: View {
#State var jsonData = [MarketChart]()
#State var priceArray = [Double]()
#State var volumeArray: [Double] = []
private let last24hpricesURL: String = "https://api.coingecko.com/api/v3/coins/bitcoin-cash-sv/market_chart?vs_currency=usd&days=1"
var body: some View {
ZStack {
VStack {
LineView(data: priceArray)
.padding()
Text("Reset")
.onTapGesture {
}
}
}
.onAppear {
getJSON(urlString: last24hpricesURL) { (data: MarketChart?) in
if let data = data {
for item in data.prices {
priceArray.append(item.last!)
}
}
}
}
}
}
struct MarketChart: Decodable {
let prices: [[Double]]
let market_caps: [[Double]]
let total_volumes: [[Double]]
}
struct CoinGeckoBSVMarketChart_Previews: PreviewProvider {
static var previews: some View {
CoinGeckoBSVMarketChart()
.preferredColorScheme(.dark)
}
}
any help with either improving the json object model or getting all the items in an array would be great

Answer 1

You have to print out the priceArray inside the completion block of getJSON method right after appending.
getJSON(urlString: "https://api.coingecko.com/api/v3/coins/bitcoin-cash-sv/market_chart?vs_currency=usd&days=1") { (data: MarketChart?) in
if let data = data {
for item in data.prices {
priceArray.append(item.first!)
}
print(priceArray)
}
}