real- time currency converter Swift - swift

Question

I'm trying to make a simple currency conversion application . here I am parsing json
static func fetchJson(key: String = "USD", completion: #escaping (ExchangeRates) -> ()) {
guard let url = URL(string: "https://open.er-api.com/v6/latest/\(String(describing: key))") else {return}
URLSession.shared.dataTask(with: url) { (data, response, error) in
if error != nil {
print(error!)
return
}
guard let safeData = data else {return}
do {
let results = try JSONDecoder().decode(ExchangeRates.self, from: safeData)
completion(results)
} catch {
print(error)
}
}.resume()
}
then I get a dictionary looks like:
"rates": {
"USD": 1,
"AED": 3.67,
"AFN": 105,
"ALL": 107.39,
"AMD": 481.52,
"ANG": 1.79,
"AOA": 538.31,
..... etc
this is how the structure in which the data is stored looks like
struct ExchangeRates: Codable {
let rates: [String: Double]
}
in the ViewController I have created an object that has the type of ExchangeRates struct and call the func fetchJson in viewDidLoad and save the result in finalCurrencies
var finalCurrencies: ExchangeRates?
then I created a tableview with the number of cells equal to
finalCurrencies.rates.count
tableViewCell has a currencyLabel with currency name (finalCurrencies.rates.key) and currencyTextField with currency value (finalCurrencies.rates.value)
extension ViewController: UITableViewDelegate, UITableViewDataSource {
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
if let currencyFetched = finalCurrencies {
return currencyFetched.rates.count
}
return 0
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
if let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath) as? TableViewCell {
if let currencyFetched = finalCurrencies {
cell.currencyLabel.text = Array(currencyFetched.rates.keys)[indexPath.row]
cell.currencyTextField.accessibilityIdentifier = Array(currencyFetched.rates.keys)[indexPath.row]
let selectedRate = Array(currencyFetched.rates.values)[indexPath.row]
cell.currencyTextField.text = "\(selectedRate)"
return cell
}
}
return UITableViewCell()
}
}
And that's what I get in the end as a result enter image description here
QUESTION: I need to make it so that when the value in the textfield for a certain currency changes, the values of the other currencies change in real- time. as a live google currency converter. I should also be able to switch between currencies and change their values, while also the values of other currencies should change. also how to make it so that with each new number an existing dictionary finalCurrencies is used and not a func fetchJson ?
I suppose that I should use this func textField (so that the textField reacts to each addition of a number).
func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
}
I'm a beginner and I've been thinking about this for a few days now and I don't know how to do it.thanks in advance.

Answer 1

First you need to calculate the ratio of the change for the currency which had its value modified, you'll then just map the values of the dictionary with that ratio:
extension Dictionary where Key == String, Value == Double {
mutating func applyChange(of currency: Key, with newValue: Value) {
guard
newValue != .zero,
let oldValue = self[currency],
oldValue != newValue,
oldValue != .zero
else { return }
let ratio = 1.0 + ((newValue - oldValue) / oldValue)
indices.forEach { values[$0] *= ratio }
}
}

Answer 2

If I've understood you correctly, I believe this would work.
Each time the user adjusts the value in the textField you'd loop through your rates dictionary, calculate the new rate and return an updated dictionary.
If I've misunderstood your goal please let me know and I'll do my best to assist :)
struct Converter {
let exchangeRates: [String: Double] = [
"USD": 1,
"AED": 3.67,
"AFN": 105,
"ALL": 107.39,
"AMD": 481.52,
"ANG": 1.79,
"AOA": 538.31
]
func convert(_ amount: String) -> [String: Double] {
var newRates = [String: Double]()
exchangeRates.forEach { (code, value) in
if let amount = Double(amount) {
newRates[code] = value * amount
}
}
return newRates
}
}
let converter = Converter()
let userInput = "10.00"
print(converter.convert(userInput))