NSUserdefault to same data from JSON - json

Question

Good morning, I have this block of code that I am using to get exchange rates from an API JSON file. I use this function to convert a result to different currencies. I am trying to add functionality to store the data so, when offline, it still shows a result with the last downloaded JSON file data.
I was thinking maybe use NSUserdefault? but not too sure where...
I am already using this to check if online or not.
if Reachability.isConnectedToNetwork(){
// connected do something}
else{
// do something else }
Thank you for any pointer and any kind of help that could send me in the right direction.
func exchangeRatefunc (mycurrency: String, mapaye: Double) {
let apiEndPoint = "https://api.fixer.io/latest?base=USD"
guard let url = NSURL(string: apiEndPoint) else {
self.infoLabel.text = NSLocalizedString("Error getting exchange rates.", comment: "")
print("Url is not valid")
return
}
let urlRequest = NSURLRequest(url: url as URL)
let session = URLSession.shared
let task = session.dataTask(with: urlRequest as URLRequest) { (data, response, error) in
guard error == nil else {
print(error?.localizedDescription ?? 0)
return
}
guard let data = data else {
print("No data received")
self.infoLabel.text = NSLocalizedString("You appear to be offline!", comment: "")
return
}
do {
guard let exchangeDict = try JSONSerialization.jsonObject(with: data, options: []) as? [String: AnyObject] else {
print("Could not convert JSON to dictionary")
self.infoLabel.text = NSLocalizedString("No conversion Available.", comment: "")
return
}
print(exchangeDict.values)
if let rates = exchangeDict["rates"] {
let currencies = [mycurrency]
for currency in currencies {
if let rate = rates[currency] as? Double {
self.exchangeRates.append("1 USD = \(rate) " + currency)
let myprefcurdisplay = mapaye * rate
OperationQueue.main.addOperation({
self.myPreferedCurrencyPayLabel.updateWithText("\(myprefcurdisplay.roundTo(places: 2)) \(currency)")
if let date = exchangeDict["date"] as? String {
self.infoLabel.text = "\(currency)/USD" + NSLocalizedString(" rates updated on" + " \(date)", comment: "")
}
})
}
}
}
}
catch {
print("Error trying to convert JSON to dictionary")
}
}
task.resume()
}