MVVM Architecture example using Retrofit Java

Model-View-VieModel (MVVM)

Model-View-ViewModel (MVVM) is a structural design pattern that separates objects into three distinct groups: Models hold application data. They're usually structs or simple classes. Views display visual elements and controls on the screen. They're typically subclasses of UIView.

build.gradle

implementation 'com.squareup.retrofit2:retrofit:2.8.1'
implementation 'com.github.bumptech.glide:glide:4.11.0'
annotationProcessor 'com.github.bumptech.glide:compiler:4.11.0'
implementation 'com.squareup.retrofit2:converter-gson:2.6.1'
implementation 'com.google.code.gson:gson:2.8.6'
implementation 'androidx.lifecycle:lifecycle-extensions:2.2.0'

AndroidManifest.xml

<uses-permission android:name="android.permission.INTERNET" />

AppConstant.java

package com.mvvm_retrofit_java.constants;

/**
 * get a api key from https://newsapi.org/
 * just register an account and request for an api key
 * when you will get an api key please replace with YOUR_API_KEY
 */

public class AppConstant {
    public static final String BASE_URL = "https://newsapi.org/v2/";
    public static final String API_KEY = "YOUR_API_KEY";
}

Article.java

package com.mvvm_retrofit_java.model;

import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;

public class Article {

    @SerializedName("urlToImage")
    @Expose
    private String urlToImage;
    @SerializedName("description")
    @Expose
    private String description;
    @SerializedName("title")
    @Expose
    private String title;

    public String getUrlToImage() {
        return urlToImage;
    }

    public void setUrlToImage(String urlToImage) {
        this.urlToImage = urlToImage;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    @Override
    public String toString() {
        return "BashboardNews{" +
                "urlToImage='" + urlToImage + '\'' +
                ", description='" + description + '\'' +
                ", title='" + title + '\'' +
                '}';
    }

}

ArticleResponse.java

package com.mvvm_retrofit_java.response;

import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;
import com.mvvm_retrofit_java.model.Article;

import java.util.List;

public class ArticleResponse {
    @SerializedName("articles")
    @Expose
    private List<Article> articles;

    public List<Article> getArticles() {
        return articles;
    }

    public void setArticles(List<Article> articles) {
        this.articles = articles;
    }

    @Override
    public String toString() {
        return "BashboardNewsResponse{" +
                "articles=" + articles +
                '}';
    }
}

RetrofitRequest.java

package com.mvvm_retrofit_java.retrofit;

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

import static com.mvvm_retrofit_java.constants.AppConstant.BASE_URL;

public class RetrofitRequest {

    private static Retrofit retrofit;


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

ApiRequest.java

package com.mvvm_retrofit_java.retrofit;

import com.mvvm_retrofit_java.response.ArticleResponse;

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

import static com.mvvm_retrofit_java.constants.AppConstant.API_KEY;

public interface ApiRequest {

    @GET("top-headlines?country=de&category=business&apiKey="+API_KEY)
    Call<ArticleResponse> getTopHeadlines();

}

ArticleRepository.java

package com.mvvm_retrofit_java.repository;

import android.util.Log;

import androidx.annotation.NonNull;
import androidx.lifecycle.LiveData;
import androidx.lifecycle.MutableLiveData;

import com.mvvm_retrofit_java.response.ArticleResponse;
import com.mvvm_retrofit_java.retrofit.ApiRequest;
import com.mvvm_retrofit_java.retrofit.RetrofitRequest;

import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;

public class ArticleRepository {
    private static final String TAG = ArticleRepository.class.getSimpleName();
    private final ApiRequest apiRequest;

    public ArticleRepository() {
        apiRequest = RetrofitRequest.getRetrofitInstance().create(ApiRequest.class);
    }

    public LiveData<ArticleResponse> getDashBoardNews() {
        final MutableLiveData<ArticleResponse> data = new MutableLiveData<>();
        apiRequest.getTopHeadlines()
                .enqueue(new Callback<ArticleResponse>() {


                    @Override
                    public void onResponse(@NonNull Call<ArticleResponse> call,
                                           @NonNull Response<ArticleResponse> response) {
                        Log.d(TAG, "onResponse response:: " + response);



                        if (response.body() != null) {
                            data.setValue(response.body());

                            Log.d(TAG, "articles total result:: " + response.body());
                            Log.d(TAG, "size:: " + response.body().getArticles().size());
//                            Log.d(TAG, "articles title pos 0:: " + response.body().getArticles().get(0).getTitle());
                        }
                    }

                    @Override
                    public void onFailure(@NonNull Call<ArticleResponse> call, @NonNull Throwable t) {
                        data.setValue(null);
                    }
                });
        return data;
    }
}

ArticleViewModel.java

package com.mvvm_retrofit_java.view_model;

import android.app.Application;

import androidx.annotation.NonNull;
import androidx.lifecycle.AndroidViewModel;
import androidx.lifecycle.LiveData;

import com.mvvm_retrofit_java.repository.ArticleRepository;
import com.mvvm_retrofit_java.response.ArticleResponse;

public class ArticleViewModel extends AndroidViewModel {

    private ArticleRepository articleResponse;
    private LiveData<ArticleResponse> articleResponseLiveData;

    public ArticleViewModel(@NonNull Application application) {
        super(application);

        articleResponse = new ArticleRepository();
        this.articleResponseLiveData = articleResponse.getDashBoardNews();
    }

    public LiveData<ArticleResponse> getBashboardNewsResponseLiveData() {
        return articleResponseLiveData;
    }
}

MovieArticleAdapter.java

package com.mvvm_retrofit_java.adapter;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

import com.bumptech.glide.Glide;
import com.mvvm_retrofit_java.R;
import com.mvvm_retrofit_java.model.Article;

import java.util.ArrayList;

public class MovieArticleAdapter extends RecyclerView.Adapter<MovieArticleAdapter.ViewHolder> {

    private final Context context;
    ArrayList<Article> articleArrayList;

    public MovieArticleAdapter(Context context, ArrayList<Article> articleArrayList) {
        this.context = context;
        this.articleArrayList = articleArrayList;
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
        View view= LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.list_each_article,viewGroup,false);
        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull ViewHolder viewHolder, int i) {
        Article article = articleArrayList.get(i);
        viewHolder.tvTitle.setText(article.getTitle());
        Glide.with(context)
                .load(article.getUrlToImage())
                .into(viewHolder.imgViewCover);
    }

    @Override
    public int getItemCount() {
        return articleArrayList.size();
    }

    public static class ViewHolder extends RecyclerView.ViewHolder {
        private final ImageView imgViewCover;
        private final TextView tvTitle;

        public ViewHolder(@NonNull View itemView) {
            super(itemView);

            imgViewCover = itemView.findViewById(R.id.imgViewCover);
            tvTitle = itemView.findViewById(R.id.tvTitle);
        }
    }
}

MainActivity.java

package com.mvvm_retrofit_java.view;

import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.ViewModelProviders;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.os.Bundle;
import android.view.View;
import android.widget.ProgressBar;

import com.mvvm_retrofit_java.R;
import com.mvvm_retrofit_java.adapter.MovieArticleAdapter;
import com.mvvm_retrofit_java.model.Article;
import com.mvvm_retrofit_java.view_model.ArticleViewModel;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    private static final String TAG = MainActivity.class.getSimpleName();

    private RecyclerView recycler_view;
    private ProgressBar progress_bar;

    private LinearLayoutManager layoutManager;
    private ArrayList<Article> articleArrayList = new ArrayList<>();
    ArticleViewModel articleViewModel;
    private MovieArticleAdapter adapter;

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

        init();

        getArticles();
    }

    private void init() {
        progress_bar = findViewById(R.id.progress_bar);
        recycler_view = findViewById(R.id.recycler_view);

        // use a linear layout manager
        layoutManager = new LinearLayoutManager(MainActivity.this);
        recycler_view.setLayoutManager(layoutManager);

        // use this setting to improve performance if you know that changes
        // in content do not change the layout size of the RecyclerView
        recycler_view.setHasFixedSize(true);

        // adapter
        adapter = new MovieArticleAdapter(MainActivity.this, articleArrayList);
        recycler_view.setAdapter(adapter);

        // View Model
        articleViewModel = ViewModelProviders.of(this).get(ArticleViewModel.class);
    }

    private void getArticles() {
        articleViewModel.getBashboardNewsResponseLiveData().observe(this, articleResponse -> {
            if (articleResponse != null  && articleResponse.getArticles() != null
                    && !articleResponse.getArticles().isEmpty()) {
                progress_bar.setVisibility(View.GONE);
                List<Article> articleList = articleResponse.getArticles();
                articleArrayList.addAll(articleList);
                adapter.notifyDataSetChanged();
            }
        });
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@android:color/black"
    tools:context=".view.MainActivity">

    <ProgressBar
        android:id="@+id/progress_bar"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true" />

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recycler_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>


</RelativeLayout>

list_each_article.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <ImageView
        android:id="@+id/imgViewCover"
        android:layout_width="match_parent"
        android:layout_height="200dp"
        android:layout_marginBottom="5dp"
        android:scaleType="centerCrop" />


    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:background="@color/transparent">
        <TextView
            android:id="@+id/tvTitle"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:textColor="@android:color/white"
            android:textStyle="bold"
            android:padding="16dp"/>
    </RelativeLayout>

</RelativeLayout>

You can work on to enhance and customize to your requirements. You can also get the project here.