使用RetroFit2和Android / Java的首次API调用

Question

I've written an iOS app and a PHP backend. Now I want to get started on the Android frontend but I have no idea what I'm doing.

My project structure looks like this:

My ApiClient:

package com.dimsumdev.runk.rest;

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

public class ApiClient {

    public static final String BASE_URL = "http://localhost/index.php/api/";
    private static Retrofit retrofit = null;

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

My ApiInterface:

package com.dimsumdev.runk.rest;

import com.dimsumdev.runk.model.*;

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

public interface ApiInterface {
    @GET("challenge/challenge/id/{id}")
    Call<Challenge> getChallenge(@Path("id") int id);
}

My Challenge model:

package com.dimsumdev.runk.model;

import com.google.gson.annotations.SerializedName;

public class Challenge {
    @SerializedName("challenge_id")
    Integer challengeId;
    @SerializedName("challenge_name")
    String challengeName;
    @SerializedName("challenge_description")
    String challengeDescription;
    @SerializedName("created")
    String created;
    @SerializedName("challenge_status")
    String challengeStatus;
}

And my HomeActivity:

package com.dimsumdev.runk.activity;

import android.support.v7.app.AppCompatActivity;
import com.dimsumdev.runk.R;
import com.dimsumdev.runk.model.*;
import android.os.Bundle;
import com.dimsumdev.runk.rest.ApiClient;
import com.dimsumdev.runk.rest.ApiInterface;
import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;

public class HomeActivity extends AppCompatActivity {

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

        ApiInterface apiService = ApiClient.getClient().create(ApiInterface.class);

        Call<Challenge> call = apiService.getChallenge(2);

        call.enqueue(new Callback<Challenge>() {

            @Override
            public void onResponse(Call<Challenge> call, Response<Challenge> response) {
                System.out.print("success");
            }

            @Override
            public void onFailure(Call<Challenge> call, Throwable t) {
                System.out.print("error");
            }
        });
    }
}

The problem is that in the HomeActivity class it keeps running into the error print. This is not what I would expect the program to do.

The backend seems to work fine in Postman:

Added this image after adding the Log.d statement in the onFailure()

Answer 1

The defined base url points to localhost, which means it expects that your phone is running your PHP backend.

Replace

public static final String BASE_URL = "http://localhost/index.php/api/";

with

public static final String BASE_URL = "http://<<ENTER-YOUR-PHP-BACKEND-MACHINE_IP>>/index.php/api/";

Even if you use a emulator (which is an own virtual device), you can not use localhost. You have to enter the IP of your machine.

Answer 2

Use the real server for example i use hostinger which gives free service upload your files and database and then check, it will work. There is no error in your code