Parsing json to swift constants - json

Question

I am trying to parse all the data from the endpoint and assign it to constants so I can use them in my ViewController class. My biggest problem is assigning each item of the "key" array to constants. Can anyone help me out?
static func fetchRates(completionHandler: (current: [Currency]) -> ()) {
let urlString = "https://api.bitcoinaverage.com/ticker/all"
let url = NSURL(string: urlString)
NSURLSession.sharedSession().dataTaskWithURL(url!, completionHandler: { (location, response, error) -> Void in
do {
let json = try(NSJSONSerialization.JSONObjectWithData(location!, options: .MutableContainers))
let tickerData = [Currency]()
for key in json as! [String : AnyObject] {
}
dispatch_async(dispatch_get_main_queue(), { () -> Void in
completionHandler(current: tickerData)
})
} catch let err as NSError {
print(err)
}
}).resume()
}
This is the response from the endpoint.
{
"AUD": {
"24h_avg": 621.17,
"ask": 624.12,
"bid": 620.3,
"last": 620.45,
"timestamp": "Mon, 23 May 2016 20:01:16 -0000",
"total_vol": 671.28
},
"BRL": {
"24h_avg": 1725.77,
"ask": 1748.83,
"bid": 1731.8,
"last": 1738.64,
"timestamp": "Mon, 23 May 2016 20:01:16 -0000",
"total_vol": 534.19
},
"CAD": {
"24h_avg": 579.2,
"ask": 579.27,
"bid": 573.57,
"last": 577.42,
"timestamp": "Mon, 23 May 2016 20:01:16 -0000",
"total_vol": 413.81
},

Answer 1

Give this a try:
for (key, value) in (json as! [String: AnyObject]) {
let currencyData = value as! [String: AnyObject]
// key is the currency code: AUD, BRL, etc
// currencyData is the details: ask, bid, last, ...
}

Answer 2

Here's a rough and ready solution, but it's a start you can build on.
Let's start by defining some convenience types:
// Define a handy result type
// See https://github.com/antitypical/Result if you want a more detailed implementation.
public enum Result<T> {
case Success(T)
case Error(ErrorType)
}
// Define an error type for inconsistentData
public enum DataError: ErrorType {
case NoData
}
// Define a struct to hold a Currency
public struct Currency: CustomStringConvertible, Equatable {
let currencyCode: String
let dayAverage: Double
let ask: Double
let bid: Double
let last: Double
let timestamp: String
let totalVolume: Double
// This makes it easier to debug
public var description: String {
return "currencyCode: \(currencyCode), dayAverage: \(dayAverage), ask: \(ask), bid: \(bid), last: \(last), timestamp: \(timestamp), totalVolume: \(totalVolume)"
}
public init(currencyCode: String,
dayAverage: Double,
ask: Double,
bid: Double,
last: Double,
timestamp: String,
totalVolume: Double) {
self.currencyCode = currencyCode
self.dayAverage = dayAverage
self.ask = ask
self.bid = bid
self.last = last
self.timestamp = timestamp
self.totalVolume = totalVolume
}
}
// Make sure your structs conform to Equatable.
public func == (lhs: Currency, rhs: Currency) -> Bool {
return
lhs.currencyCode == rhs.currencyCode &&
lhs.dayAverage == rhs.dayAverage &&
lhs.ask == rhs.ask &&
lhs.bid == rhs.bid &&
lhs.last == rhs.last &&
lhs.timestamp == rhs.timestamp &&
lhs.totalVolume == rhs.totalVolume
}
// I like to define convenience initialisers outside of the struct. Keeps things less coupled.
public extension Currency {
public init?(currencyCode: String, values: [String : AnyObject]) {
guard
let dayAverage = values["24h_avg"] as? Double,
let ask = values["ask"] as? Double,
let bid = values["bid"] as? Double,
let last = values["last"] as? Double,
let timestamp = values["timestamp"] as? String,
let totalVolume = values["total_vol"] as? Double
else { return nil }
self = Currency(currencyCode: currencyCode,
dayAverage: dayAverage,
ask: ask,
bid: bid,
last: last,
timestamp: timestamp,
totalVolume: totalVolume)
}
}
Now the function to fetch the values can be written as:
// The function to fetch the currencies.
// Use a richer type for the completion parameter. It is either a success with a list of currencies or an error.
public func fetchRates(completionHandler: (Result<[Currency]>) -> ()) {
let url = NSURL(string: "https://api.bitcoinaverage.com/ticker/all")! // Force unwrapped as we assume this is a valid URL
NSURLSession.sharedSession().dataTaskWithURL(url) { (data, _, error) in
if let error = error {
completionHandler(.Error(error))
return
}
do {
guard
let data = data,
// Being generous with the type of the result because there is a top level key that is the timestamp not related to a currency.
let json = try NSJSONSerialization.JSONObjectWithData(data, options: .MutableContainers) as? [String : AnyObject]
else {
completionHandler(.Error(DataError.NoData))
return
}
var currencies = [Currency]()
for (key, value) in json {
guard
// Make sure that the values we are about to pass on are of the correct type.
let value = value as? [String : AnyObject],
let currency = Currency(currencyCode: key, values: value)
else { continue }
currencies.append(currency)
}
print(currencies)
completionHandler(.Success(currencies))
} catch {
completionHandler(.Error(error))
}
}.resume()
}
And you can run this function with the completion handlers as:
fetchRates { result in
dispatch_async(dispatch_get_main_queue()) {
switch result {
case .Success(let currencies):
for currency in currencies {
print(currency)
}
case .Error(let error):
print(error)
}
}
}
You can download the playground where you can see all this working at:
https://dl.dropboxusercontent.com/u/585261/Currency.playground.zip