Extract data from closure using completion in swift [duplicate] - swift

Question

This question already has answers here:
Returning data from async call in Swift function
(13 answers)
Closed 1 year ago.
First of all, this is my first attempt at Swift so I'm not really sure what I'm doing. I'm learning as I go right now and have hit a roadblock.
I'm trying to implement a WatchOS app that will call an API on a set timer to track fluctuations in some crypto prices.
I have figured out how to make the API call and get the JSON parsed to a point where I can print the data but I'm struggling to get it out of the closure and to my interface. I know the proper way to do this is with a completion handler but I can't seem to get a solid understanding of how to make that work in this scenario.
Any help would be appreciated
import SwiftUI
var refresh = bitcoin()
var btc: String = refresh
var eth: String = "ETH"
var doge: String = "DOGE"
struct ContentView: View {
var body: some View {
VStack(alignment: .leading ){
Label("\(btc)", image: "eth").padding(.vertical, 10.0)
Label("\(eth)", image: "eth").padding(.vertical, 10.0)
Label("\(doge)", image: "doge").padding(.vertical, 10.0)
}
.scaledToFill()
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
import Foundation
#if canImport(FoundationNetworking)
import FoundationNetworking
#endif
struct responseData: Codable{
let data: Response?
}
struct Response: Codable{
var id: String
var rank: String
var symbol: String
var name: String
var supply: String
var maxSupply: String
var marketCapUsd: String
var volumeUsd24Hr: String
var priceUsd: String
var changePercent24Hr: String
var vwap24Hr: String
}
func bitcoin() -> String{
var result: String = "btc"
var request = URLRequest(url: URL(string: "https://api.coincap.io/v2/assets/bitcoin")!,timeoutInterval: Double.infinity)
request.httpMethod = "GET"
let task = URLSession.shared.dataTask(with: request) { data, response, error in
guard let data = data else {
print(String(describing: error))
return
}
let response = try! JSONDecoder().decode(responseData.self, from: data)
result = (response.data?.priceUsd)!
print(result)
}
task.resume()
return result
}

Answer 1

There many ways to achieve what you want, one way is to use "ObservableObject". Try something like this:
import SwiftUI
#main
struct TestApp: App {
var body: some Scene {
WindowGroup {
ContentView()
}
}
}
class CoinModel: ObservableObject {
#Published var btcPriceUsd = "not yet available"
#Published var ethPriceUsd = "not yet available"
#Published var dogePriceUsd = "not yet available"
}
struct ContentView: View {
#StateObject var coins = CoinModel()
var body: some View {
VStack(alignment: .leading ){
Label("\(coins.btcPriceUsd)", image: "btc").padding(.vertical, 10.0)
Label("\(coins.ethPriceUsd)", image: "eth").padding(.vertical, 10.0)
Label("\(coins.dogePriceUsd)", image: "doge").padding(.vertical, 10.0)
}
.scaledToFill()
.onAppear {
// bitcoin()
bitcoin2 { price in
coins.btcPriceUsd = price
}
}
}
func bitcoin() {
var request = URLRequest(url: URL(string: "https://api.coincap.io/v2/assets/bitcoin")!,timeoutInterval: Double.infinity)
request.httpMethod = "GET"
let task = URLSession.shared.dataTask(with: request) { data, response, error in
guard let data = data else {
return
}
let response = try! JSONDecoder().decode(responseData.self, from: data)
if let respData = response.data {
DispatchQueue.main.async {
coins.btcPriceUsd = respData.priceUsd
}
}
}
task.resume()
}
}
EDIT: if you really want to use completion, then try this:
func bitcoin2(completion: #escaping (String) -> Void) {
var request = URLRequest(url: URL(string: "https://api.coincap.io/v2/assets/bitcoin")!,timeoutInterval: Double.infinity)
request.httpMethod = "GET"
let task = URLSession.shared.dataTask(with: request) { data, response, error in
guard let data = data else {
return completion("")
}
let response = try! JSONDecoder().decode(responseData.self, from: data)
if let respData = response.data {
DispatchQueue.main.async {
completion(respData.priceUsd)
}
}
}
task.resume()
}