How can I update Activity/Fragment UI from Retrofit onResponse()?

Question

I want to use Retrofit 2.1.0 for my next Android project. I would like to use Design Pattern and therefore create separate classes for every REST call i.e

IBalanceServ

Answer 1

 public class BalanceRestClient {

            private static BalanceRestClient instance;
            private IBalanceService request;

            private BalanceRestClient() {
                Retrofit retrofit = new Retrofit.Builder()
                        .baseUrl("http://hovermind.com")
                        .addConverterFactory(GsonConverterFactory.create())
                        .addCallAdapterFactory(rxAdapter)
                        .build();

                request = retrofit.create(IBalanceService.class);
            }

            public static synchronized BalanceRestClient getInstance() {
                if (instance == null)
                    instance = new BalanceRestClient();

                return instance;
            }

            public void getRequest(String userName, YourCustomeCallback callback) {

                Call call = apiService.getUser(username);
                call.enqueue(new Callback() {

                    @Override
                    public void onResponse(Call call, Response response) {

                        User user = response.body();

                        callback.onResponse(user);

                    }

                    @Override
                    public void onFailure(Call call, Throwable t) {
                        // Log error here since request failed
                    }

                });
            }
        }

1. Create a singleton class. Its init a request only once.
2. Create a custom callback, which will give back your response to UI.
3. Call BalanceRestClient.getInstance.getRequest(params..) where you want to use it.