Dynamically Changing the Base Currency - swiftui

Question

I have a currency API that returns a JSON object containing a strange arrangement: the base currency is used as a label. Typical currency APIs have labels like "base", "date", "success", and "rates", but this API doesn't have any of those.
{
"usd": {
"aed": 4.420217,
"afn": 93.3213,
"all": 123.104693,
"amd": 628.026474,
"ang": 2.159569,
"aoa": 791.552347,
"ars": 111.887966,
"aud": 1.558363,
"awg": 2.164862,
"azn": 2.045728,
"bam": 1.9541,
"bbd": 2.429065,
"bch": 0.001278
}
}
The "usd" (US dollars) at the top is called the base or home currency. At the moment the storage structure and state parameter are hardcoded to "usd" which prevents using exchange rates with other base currencies. The exchange rate API works great for a base currency of US dollars.
I need help modifying things so that I can download the exchange rates with different base currencies. For example, can I use a string variable in the storage model and state parameter? Any enlightenment will be greatly appreciated.
struct RateResult: Codable {
let usd: [String: Double]
}
#State private var results = RateResult(usd: [:])
struct ContentView: View {
var body: some View {
}
func UpdateRates() {
let baseUrl = "https://cdn.jsdelivr.net/gh/fawazahmed0/currency-api#1/latest/currencies/"
let baseCur = baseCurrency.baseCur.baseS // usd
let requestType = ".json"
guard let url = URL(string: baseUrl + baseCur + requestType) else {
print("Invalid URL")
return
}
let request = URLRequest(url: url)
URLSession.shared.dataTask(with: request) { data, response, error in
if let data = data {
if let decodedResponse = try? JSONDecoder().decode(RateResult.self, from: data) {
// we have good data – go back to the main thread
DispatchQueue.main.async {
// update our UI
self.results = decodedResponse
// save off currency exchange rates
}
// everything is good, so we can exit
return
}
}
// if we're still here it means there was a problem
print("Currency Fetch Failed: \(error?.localizedDescription ?? "Unknown error")")
}.resume()
}
}

Answer 1

import SwiftUI
//You can't use the standard Codable for this. You have to make your own.
class BaseCurrency: Codable {
let id = UUID()
var baseCurrencies: [String : [String: Double]] = [:]
required public init(from decoder: Decoder) throws {
do{
print(#function)
let baseContainer = try decoder.singleValueContainer()
let base = try baseContainer.decode([String : [String: Double]].self)
for key in base.keys{
baseCurrencies[key] = base[key]
}
}catch{
print(error)
throw error
}
}
//#State should never be used outside a struct that is a View
}
struct CurrencyView: View {
#StateObject var vm: CurrencyViewModel = CurrencyViewModel()
var body: some View {
VStack{
List{
if vm.results != nil{
ForEach(vm.results!.baseCurrencies.sorted{$0.key < $1.key}, id: \.key) { key, baseCurrency in
DisclosureGroup(key){
ForEach(baseCurrency.sorted{$0.key < $1.key}, id: \.key) { key, rate in
HStack{
Text(key)
Text(rate.description)
}
}
}
}
}else{
Text("waiting...")
}
}
//To select another rate to go fetch
RatesPickerView().environmentObject(vm)
}.onAppear(){
vm.UpdateRates()
}
}
}
struct RatesPickerView: View {
#EnvironmentObject var vm: CurrencyViewModel
var body: some View {
if vm.results != nil{
//You can probaly populate this picker with the keys in
// baseCurrency.baseCur.baseS
Picker("rates", selection: $vm.selectedBaseCurrency){
ForEach((vm.results!.baseCurrencies.first?.value.sorted{$0.key < $1.key})!, id: \.key) { key, rate in
Text(key).tag(key)
}
}
}else{
Text("waiting...")
}
}
}
class CurrencyViewModel: ObservableObject{
#Published var results: BaseCurrency?
#Published var selectedBaseCurrency: String = "usd"{
didSet{
UpdateRates()
}
}
init() {
//If you can .onAppear you don't need it here
//UpdateRates()
}
func UpdateRates() {
print(#function)
let baseUrl = "https://cdn.jsdelivr.net/gh/fawazahmed0/currency-api#1/latest/currencies/"
let baseCur = selectedBaseCurrency // usd
let requestType = ".json"
guard let url = URL(string: baseUrl + baseCur + requestType) else {
print("Invalid URL")
return
}
let request = URLRequest(url: url)
URLSession.shared.dataTask(with: request) { data, response, error in
if let data = data {
do{
let decodedResponse = try JSONDecoder().decode(BaseCurrency.self, from: data)
DispatchQueue.main.async {
if self.results == nil{
//Assign a new base currency
self.results = decodedResponse
}else{ //merge the existing with the new result
for base in decodedResponse.baseCurrencies.keys{
self.results?.baseCurrencies[base] = decodedResponse.baseCurrencies[base]
}
}
//update the UI
self.objectWillChange.send()
}
}catch{
//Error thrown by a try
print(error)//much more informative than error?.localizedDescription
}
}
if error != nil{
//data task error
print(error!)
}
}.resume()
}
}
struct CurrencyView_Previews: PreviewProvider {
static var previews: some View {
CurrencyView()
}
}