When developing an iOS app, there’s a good chance you’ll need to download data from a server. You can do that using an HTTP GET request. You can obtain data from an API endpoint on a server easily by sending a GET request with the required parameters to the server. The following code example downloads a JSON array containing exchange rates from an exchange’s ‘ticker’ API endpoint and parses the first JSON object in that array to extract the desired exchange rate data. I only parsed the first one (array member 0) to keep this example as short as possible.

Key details:

  • The API endpoint used in the following Swift GET request example is: ‘/api/v3/ticker/price’.
  • The API provider is ‘binance.com’.
  • No parameters were required by this particular endpoint, but other endpoints do require them. A parameter is usually at the end of the URL the GET request is being sent to, starting with a question sign. For example ‘?tradingpair=’ is the parameter required by this endpoint, and you provide it with the trading pair which is ‘btcusdt’: ‘http://kompulsa.ch:8080/bncryptoprice?tradingpair=btcusdt‘.
  • Like other languages, Swift GET requests encode parameters in the URL instead of in the request body (unlike a POST request).
  • The ‘guard’ statements are there to abandon execution if a task fails. That’s an error-handling method.
  • ‘queue.async’ and ‘DispatchQueue’ code are not required in all cases, but you do need them if you are trying to update a label in UIKit because UIKit requires that you do that on the main thread.

let queue = DispatchQueue(label: “lbPrice”);

        queue.async {

            guard let url = URL(string: https://api.binance.com/api/v3/ticker/price) else {return}

            //Preparing and sending off the GET request:

            let task = URLSession.shared.dataTask(with: url) { (data, response, error) in

            guard let dataResponse = data,

                      error == nil else {

                        print(error?.localizedDescription ?? “Response Error”);

                      return }

                do{

                    //Store the server’s response in the jsonResponse variable

                    let jsonResponse = try JSONSerialization.jsonObject(with:

                                                                            dataResponse, options: []);

                    

                    guard let jsonArray = jsonResponse as? [[String: Any]] else {

                        return; //Executed if the statement above fails

                    }

                    //Start parsing out specific values, for example: ‘symbol’ or ‘price’

                    guard let symbol = jsonArray[0][symbol] as? String

                    else

                    {

                        return;

                    }

                    guard let price = jsonArray[0][price] as? String else {

                        return;

                    }

                    DispatchQueue.main.async {

                        self.priceLB1.text = symbol + “: “ + price; //Update the label on the main thread with the data we downloaded.

                    }

                    

                 } catch let parsingError {

                    print(“Error”, parsingError);

               }

                

            }

            task.resume();

        }