How to Build a Bitcoin Tracker Android App?

package org.geeksforgeeks.bitcointracker;

import java.util.Map;

public class BitcoinResponse {
    private Map<String, String> rates;

    public BitcoinResponse(Map<String, String> rates) {
        this.rates = rates;
    }

    public Map<String, String> getRates() {
        return rates;
    }

    public void setRates(Map<String, String> rates) {
        this.rates = rates;
    }
}

package org.geeksforgeeks.bitcointracker;

import retrofit2.Call;
import retrofit2.http.GET;
import retrofit2.http.Query;

public interface BitcoinApiService {

    @GET("live")
    Call<BitcoinResponse> getBitcoinPrice(
        @Query("access_key") String accessKey,
        @Query("TARGET") String target,
        @Query("symbols") String symbols
    );
}

package org.geeksforgeeks.bitcointracker;

import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;

public class RetrofitInstance {

    private static final String BASE_URL = "https://api.coinlayer.com/";

    private static Retrofit retrofit;

    public static BitcoinApiService getApi() {
        if (retrofit == null) {
            retrofit = new Retrofit.Builder()
                    .baseUrl(BASE_URL)
                    .addConverterFactory(GsonConverterFactory.create())
                    .build();
        }
        return retrofit.create(BitcoinApiService.class);
    }
}

package org.geeksforgeeks.bitcointracker;

import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Spinner;
import android.widget.TextView;

import androidx.appcompat.app.AppCompatActivity;

import java.io.IOException;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

import retrofit2.Call;
import retrofit2.Response;

public class MainActivity extends AppCompatActivity {
    private final String apiKey = "YOUR_API_KEY"; // Add your API key here
    private TextView mPriceTextView;
    private final BitcoinApiService apiService = RetrofitInstance.getApi();
    private final ExecutorService executorService = Executors.newSingleThreadExecutor();
    private final List<String> currencyArray = Arrays.asList("AUD", "BRL", "CAD", "CNY", "EUR", "GBP",
            "HKD", "JPY", "PLN", "RUB", "SEK", "USD", "ZAR");

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Initialize TextView for displaying Bitcoin price
        mPriceTextView = findViewById(R.id.priceLabel);
        Spinner spinner = findViewById(R.id.currency_spinner);

        // Set up the spinner (dropdown) with currency options
        ArrayAdapter<String> adapter = new ArrayAdapter<>(this, R.layout.spinner_item, currencyArray);
        adapter.setDropDownViewResource(R.layout.spinner_item);
        spinner.setAdapter(adapter);

        // Handle currency selection from the spinner
        spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> adapterView, View view, int position, long id) {
                String currency = adapterView.getItemAtPosition(position).toString();
                fetchBitcoinPrice(currency); // Fetch Bitcoin price for selected currency
            }

            @Override
            public void onNothingSelected(AdapterView<?> adapterView) {
            }
        });
    }

    // Fetch Bitcoin price from the API using a background thread
    private void fetchBitcoinPrice(String currency) {
        executorService.execute(() -> {
            try {
                // Make the network request
                Call<BitcoinResponse> call = apiService.getBitcoinPrice(apiKey, currency);
                Response<BitcoinResponse> response = call.execute();

                if (response.isSuccessful() && response.body() != null) {
                    // Extract price from response
                    String price = response.body().getRates().get("BTC");
                    if (price == null) price = "N/A";

                    // Update UI on the main thread
                    final String finalPrice = price;
                    runOnUiThread(() -> mPriceTextView.setText(finalPrice));
                } else {
                    runOnUiThread(() -> mPriceTextView.setText("Error"));
                }
            } catch (IOException e) {
                Log.e("BitcoinTracker", "Error fetching data", e);
                runOnUiThread(() -> mPriceTextView.setText("Error"));
            }
        });
    }
}