Android Studio：API 调用 - 如何从 JSON 对象读取对象

Question

I'm building a currency conversion application by using a public API. In my code, I need to read the conversion_rates part of this JSON Object:

{"result":"success","documentation":"https://www.exchangerate-api.com/docs","terms_of_use":"https://www.exchangerate-api.com/terms","time_last_update_unix":1604275451,"time_last_update_utc":"Mon, 02 Nov 2020 00:04:11 +0000","time_next_update_unix":1604361971,"time_next_update_utc":"Tue, 03 Nov 2020 00:06:11 +0000","base_code":"USD","conversion_rates":{"USD":1,"AED":3.6720,"ARS":78.2978,"AUD":1.4207,"BGN":1.6731,"BRL":5.7739,"BSD":1.0000,"CAD":1.3323,"CHF":0.9158,"CLP":771.5889,"CNY":6.6867,"COP":3852.2500,"CZK":23.3398,"DKK":6.3721,"DOP":58.1472,"EGP":15.6627,"EUR":0.8571,"FJD":2.1386,"GBP":0.7722,"GTQ":7.7863,"HKD":7.7528,"HRK":6.4788,"HUF":314.5384,"IDR":14686.5055,"ILS":3.4125,"INR":74.4728,"ISK":140.9082,"JPY":104.5730,"KRW":1133.2948,"KZT":432.8371,"MVR":15.2900,"MXN":21.2752,"MYR":4.1540,"NOK":9.5245,"NZD":1.5077,"PAB":1.0000,"PEN":3.6123,"PHP":48.4156,"PKR":159.8444,"PLN":3.9539,"PYG":7004.0909,"RON":4.1695,"RUB":79.1120,"SAR":3.7504,"SEK":8.8849,"SGD":1.3645,"THB":31.1583,"TRY":8.3641,"TWD":28.5836,"UAH":28.4108,"UYU":42.9699,"ZAR":16.2831}}

When I try to debug my mainActivity.java at the line where log the API response, I see nothing in my debugging console! I believe it must be a problem with reading from the JSON object. This is my first time using APIs with android studio, so I'm not sure if I did it correctly. Here are my codes

MainActivity.java:

package com.example.currencyconversion;

import androidx.appcompat.app.AppCompatActivity;
import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;

import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;

import com.example.currencyconversion.Retrofit.RetrofitBuilder;
import com.example.currencyconversion.Retrofit.RetrofitInterface;
import com.google.gson.JsonObject;

public class MainActivity extends AppCompatActivity {

    Button button;
    EditText currencyToBeConverted;
    EditText currencyConverted;
    Spinner convertToDropdown;
    Spinner convertFromDropdown;

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

        // Initialization
        currencyConverted =(EditText) findViewById(R.id.currency_converted);
        currencyToBeConverted =(EditText) findViewById(R.id.currency_to_be_converted);
        convertToDropdown = (Spinner) findViewById(R.id.convert_to);
        convertFromDropdown = (Spinner) findViewById(R.id.convert_from);
        button = (Button) findViewById(R.id.button);

       // Adding Functionality
        String[] downDownList = {"USD", "AED", "EUR", "GBP"};
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, R.layout.support_simple_spinner_dropdown_item, downDownList);
        convertToDropdown.setAdapter(adapter);
        convertFromDropdown.setAdapter(adapter);


        button.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View view) {
                //API Call
                RetrofitInterface retrofitInterface = RetrofitBuilder.getRetrofitInstance().create(RetrofitInterface.class);
                //Call<JsonObject> call = retrofitInterface.getExchangeCurrency(convertFromDropdown.getSelectedItem().toString());
                Call<JsonObject> call = retrofitInterface.getExchangeCurrency("AED");
                call.enqueue(new Callback<JsonObject>() {
                    @Override
                    public void onResponse(Call<JsonObject> call, Response<JsonObject> response) {
                        Log.d("response", String.valueOf(response.body())); //HERE IS WHERE I DEBUG


                        /*JsonObject res = response.body();
                        JsonObject rates = res.getAsJsonObject("conversion_rates");
                        double currency = Double.valueOf(currencyToBeConverted.getText().toString());
                        double multiplier = Double.valueOf(rates.get(convertToDropdown.getSelectedItem().toString()).toString());
                        double result = currency * multiplier;
                        currencyConverted.setText(String.valueOf(result));*/

                    }

                    @Override
                    public void onFailure(Call<JsonObject> call, Throwable t) {

                    }
                });
            }
        });


    }

RetrofitBuilder.java:

package com.example.currencyconversion.Retrofit;

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

public class RetrofitBuilder {
    public static Retrofit retrofit;
    public static Retrofit getRetrofitInstance() {
        if (retrofit == null) {
            retrofit = new Retrofit.Builder()
                    .baseUrl("https://v6.exchangerate-api.com/")
                    .addConverterFactory(GsonConverterFactory.create())
                    .build();
        }

        return retrofit;
    }
}

RetrofitInterface.java:

package com.example.currencyconversion.Retrofit;

import com.google.gson.JsonObject;

import retrofit2.Call;
import retrofit2.http.GET;
import retrofit2.http.Path;

public interface RetrofitInterface {
    @GET("v6/4API-KEY/latest/{currency}")
    Call<JsonObject> getExchangeCurrency(@Path("currency") String currency);
}

Answer 1

Here is why you're not getting an error..

You're getting a result from your API using an INVALID KEY which is "AED" as stated on your code.

Here's the link of your request: https://v6.exchangerate-api.com/v6/4API-KEY/latest/AED

And this is the result that the API is outputting:

{
   "result":"error","error-type":"invalid-key"
}

I recommend to check your APIs documentation.

Answer 2

I tried and modified your code a bit... Here's a working one.

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.util.Log;
import android.view.inputmethod.EditorInfo;
import android.widget.ArrayAdapter;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.TextView;

import com.google.gson.JsonObject;

import java.text.DecimalFormat;

import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;
import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;
import retrofit2.http.GET;
import retrofit2.http.Path;

public class MainActivity extends AppCompatActivity
{
    private Spinner from_conversions;
    private Spinner to_conversions;
    private EditText target;
    private TextView tv;

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

        from_conversions = findViewById(R.id.from_conversions);
        to_conversions = findViewById(R.id.to_conversions);
        target = findViewById(R.id.target);
        tv = findViewById(R.id.test);

        target.setOnEditorActionListener((textview, id, event) -> {
            if(id == 1 || id == EditorInfo.IME_ACTION_GO)
            {
                if(!target.getText().toString().isEmpty())
                    convert(to_conversions.getSelectedItem().toString(), from_conversions.getSelectedItem().toString());
                return true;
            }

            return false;
        });

        String[] currencies = {"AED", "EUR", "USD", "GBP"};
        ArrayAdapter<String> adapter = new ArrayAdapter<>(this, android.R.layout.simple_spinner_dropdown_item, currencies);

        to_conversions.setAdapter(adapter);
        to_conversions.setSelection(1);

        from_conversions.setAdapter(adapter);
        from_conversions.setSelection(1);
    }

    private void convert(final String to, final String from)
    {
        CurrencyAPI api = getRetrofit().create(CurrencyAPI.class);
        Call<JsonObject> call = api.getExchangeCurrency(from);
        call.enqueue(new Callback<JsonObject>() {
            @Override
            public void onResponse(@NonNull  Call<JsonObject> call, @NonNull Response<JsonObject> response)
            {
                Log.e(MainActivity.class.getSimpleName(), response.body().toString());

                JsonObject json = response.body();
                JsonObject rates = json.getAsJsonObject("conversion_rates");

                String str_conversionValue = rates.get(to).toString();
                String str_numberToConvert = target.getText().toString();

                DecimalFormat formatter = new DecimalFormat("#.##");
                double conversionValue = Double.parseDouble(str_conversionValue); // multiplier variable on your code
                double numberToConvert = Double.parseDouble(str_numberToConvert); // currency variable on your code
                double result = numberToConvert * conversionValue;
                tv.setText(String.valueOf("Result: " + formatter.format(result) + " " + to));
            }

            @Override
            public void onFailure(@NonNull Call<JsonObject> call, @NonNull Throwable t)
            {}
        });
    }

    private Retrofit getRetrofit()
    {
        return (new Retrofit.Builder()
                .addConverterFactory(GsonConverterFactory.create())
                .baseUrl("https://v6.exchangerate-api.com/v6/4a831cb7beb97c0912c27dda/")
                .build());
    }

    private interface CurrencyAPI {
        @GET("latest/{currency}")
        Call<JsonObject> getExchangeCurrency(@Path("currency") String currency);
    }
}