Add Retrofit networking lesson

app/build.gradle

@@ -100,6 +100,8 @@ dependencies {
     implementation libs.androidx.room.runtime
     annotationProcessor libs.androidx.room.compiler
     annotationProcessor libs.glide.compiler
+    implementation libs.retrofit2
+    implementation libs.retrofit2.converter.gson
 
     // Testing
     testImplementation libs.junit

app/src/main/AndroidManifest.xml

@@ -316,6 +316,18 @@
             android:label="@string/room_database"
             android:parentActivityName=".ui.screens.android.lessons.data.room.RoomActivity" />
 
+        <activity
+            android:name=".ui.screens.android.lessons.networking.retrofit.RetrofitActivity"
+            android:exported="false"
+            android:label="@string/retrofit"
+            android:parentActivityName=".ui.screens.main.MainActivity" />
+
+        <activity
+            android:name=".ui.screens.android.lessons.networking.retrofit.RetrofitCodeActivity"
+            android:exported="false"
+            android:label="@string/retrofit"
+            android:parentActivityName=".ui.screens.android.lessons.networking.retrofit.RetrofitActivity" />
+
         <activity
             android:name=".ui.screens.settings.SettingsActivity"
             android:exported="false"

app/src/main/assets/quiz_questions.json

@@ -23,5 +23,10 @@
     "question": "What component shows a scrollable list of items?",
     "options": ["RecyclerView", "TextView", "ImageView", "Button"],
     "answer": 0
+  },
+  {
+    "question": "Which library simplifies HTTP requests by turning APIs into interfaces?",
+    "options": ["Volley", "Retrofit", "Glide", "Room"],
+    "answer": 1
   }
 ]

app/src/main/java/com/d4rk/androidtutorials/java/ui/screens/android/lessons/networking/retrofit/RetrofitActivity.java

@@ -0,0 +1,86 @@
+package com.d4rk.androidtutorials.java.ui.screens.android.lessons.networking.retrofit;
+
+import android.content.Intent;
+import android.os.Bundle;
+import android.os.Handler;
+import android.os.Looper;
+
+import androidx.annotation.Nullable;
+
+import com.d4rk.androidtutorials.java.databinding.ActivityRetrofitBinding;
+import com.d4rk.androidtutorials.java.ui.components.navigation.UpNavigationActivity;
+import com.d4rk.androidtutorials.java.utils.EdgeToEdgeDelegate;
+
+import com.d4rk.androidtutorials.java.R;
+
+import retrofit2.Call;
+import retrofit2.Callback;
+import retrofit2.Response;
+import retrofit2.Retrofit;
+import retrofit2.converter.gson.GsonConverterFactory;
+import retrofit2.http.GET;
+
+/**
+ * Demonstrates a simple HTTP request using Retrofit.
+ */
+public class RetrofitActivity extends UpNavigationActivity {
+    private ActivityRetrofitBinding binding;
+    private final Handler handler = new Handler(Looper.getMainLooper());
+    private JsonPlaceholderApi api;
+
+    interface JsonPlaceholderApi {
+        @GET("todos/1")
+        Call<Todo> getTodo();
+    }
+
+    static class Todo {
+        public String title;
+    }
+
+    @Override
+    protected void onCreate(@Nullable Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+        binding = ActivityRetrofitBinding.inflate(getLayoutInflater());
+        setContentView(binding.getRoot());
+
+        EdgeToEdgeDelegate edgeToEdgeDelegate = new EdgeToEdgeDelegate(this);
+        edgeToEdgeDelegate.applyEdgeToEdge(binding.constraintLayout);
+
+        Retrofit retrofit = new Retrofit.Builder()
+                .baseUrl("https://jsonplaceholder.typicode.com/")
+                .addConverterFactory(GsonConverterFactory.create())
+                .build();
+        api = retrofit.create(JsonPlaceholderApi.class);
+
+        binding.buttonFetch.setOnClickListener(v -> {
+            binding.buttonFetch.setEnabled(false);
+            api.getTodo().enqueue(new Callback<Todo>() {
+                @Override
+                public void onResponse(Call<Todo> call, Response<Todo> response) {
+                    if (response.isSuccessful() && response.body() != null) {
+                        binding.textViewResult.setText(response.body().title);
+                    } else {
+                        binding.textViewResult.setText(R.string.snack_general_error);
+                    }
+                    binding.buttonFetch.setEnabled(true);
+                }
+
+                @Override
+                public void onFailure(Call<Todo> call, Throwable t) {
+                    binding.textViewResult.setText(R.string.snack_general_error);
+                    binding.buttonFetch.setEnabled(true);
+                }
+            });
+        });
+
+        binding.floatingButtonShowSyntax.setOnClickListener(v ->
+                startActivity(new Intent(RetrofitActivity.this, RetrofitCodeActivity.class)));
+        handler.postDelayed(() -> binding.floatingButtonShowSyntax.shrink(), 5000);
+    }
+
+    @Override
+    protected void onDestroy() {
+        super.onDestroy();
+        handler.removeCallbacksAndMessages(null);
+    }
+}

app/src/main/java/com/d4rk/androidtutorials/java/ui/screens/android/lessons/networking/retrofit/RetrofitCodeActivity.java

@@ -0,0 +1,80 @@
+package com.d4rk.androidtutorials.java.ui.screens.android.lessons.networking.retrofit;
+
+import android.os.Bundle;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import androidx.fragment.app.Fragment;
+import androidx.viewpager2.adapter.FragmentStateAdapter;
+
+import com.d4rk.androidtutorials.java.R;
+import com.d4rk.androidtutorials.java.databinding.ActivityTabLayoutBinding;
+import com.d4rk.androidtutorials.java.ui.components.navigation.UpNavigationActivity;
+import com.d4rk.androidtutorials.java.ui.screens.android.lessons.networking.retrofit.tabs.RetrofitTabCodeFragment;
+import com.d4rk.androidtutorials.java.ui.screens.android.lessons.networking.retrofit.tabs.RetrofitTabLayoutFragment;
+import com.d4rk.androidtutorials.java.utils.EdgeToEdgeDelegate;
+import com.google.android.material.tabs.TabLayoutMediator;
+
+import java.util.ArrayList;
+
+/**
+ * Displays Java and XML snippets for the Retrofit example.
+ */
+public class RetrofitCodeActivity extends UpNavigationActivity {
+    private ActivityTabLayoutBinding binding;
+
+    @Override
+    protected void onCreate(@Nullable Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+        binding = ActivityTabLayoutBinding.inflate(getLayoutInflater());
+        setContentView(binding.getRoot());
+
+        EdgeToEdgeDelegate edgeToEdgeDelegate = new EdgeToEdgeDelegate(this);
+        edgeToEdgeDelegate.applyEdgeToEdge(binding.appBarLayout);
+
+        setupViewPager();
+
+        new TabLayoutMediator(binding.tabs, binding.viewpager, (tab, position) -> {
+            ViewPagerAdapter adapter = (ViewPagerAdapter) binding.viewpager.getAdapter();
+            if (adapter != null) {
+                tab.setText(adapter.getPageTitle(position));
+            }
+        }).attach();
+    }
+
+    private void setupViewPager() {
+        ViewPagerAdapter adapter = new ViewPagerAdapter(this);
+        adapter.addFragment(new RetrofitTabCodeFragment(), getString(R.string.code_java));
+        adapter.addFragment(new RetrofitTabLayoutFragment(), getString(R.string.layout_xml));
+        binding.viewpager.setAdapter(adapter);
+    }
+
+    private static class ViewPagerAdapter extends FragmentStateAdapter {
+        private final ArrayList<Fragment> fragmentList = new ArrayList<>();
+        private final ArrayList<String> fragmentTitleList = new ArrayList<>();
+
+        ViewPagerAdapter(@NonNull UpNavigationActivity activity) {
+            super(activity);
+        }
+
+        void addFragment(@NonNull Fragment fragment, @NonNull String title) {
+            fragmentList.add(fragment);
+            fragmentTitleList.add(title);
+        }
+
+        @NonNull
+        @Override
+        public Fragment createFragment(int position) {
+            return fragmentList.get(position);
+        }
+
+        @Override
+        public int getItemCount() {
+            return fragmentList.size();
+        }
+
+        CharSequence getPageTitle(int position) {
+            return fragmentTitleList.get(position);
+        }
+    }
+}

app/src/main/java/com/d4rk/androidtutorials/java/ui/screens/android/lessons/networking/retrofit/tabs/RetrofitTabCodeFragment.java

@@ -0,0 +1,58 @@
+package com.d4rk.androidtutorials.java.ui.screens.android.lessons.networking.retrofit.tabs;
+
+import android.content.SharedPreferences;
+import android.graphics.Typeface;
+import android.os.Bundle;
+import android.util.Log;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+
+import androidx.annotation.NonNull;
+import androidx.fragment.app.Fragment;
+import androidx.preference.PreferenceManager;
+
+import com.d4rk.androidtutorials.java.R;
+import com.d4rk.androidtutorials.java.databinding.FragmentCodeBinding;
+import com.d4rk.androidtutorials.java.utils.CodeHighlighter;
+import com.d4rk.androidtutorials.java.utils.CodeViewUtils;
+import com.d4rk.androidtutorials.java.utils.FontManager;
+import com.google.android.gms.ads.AdRequest;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+
+import me.zhanghai.android.fastscroll.FastScrollerBuilder;
+
+/**
+ * Shows the Java implementation for the Retrofit example.
+ */
+public class RetrofitTabCodeFragment extends Fragment {
+
+    @Override
+    public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
+        FragmentCodeBinding binding = FragmentCodeBinding.inflate(inflater, container, false);
+        new FastScrollerBuilder(binding.scrollView).useMd2Style().build();
+        binding.adView.loadAd(new AdRequest.Builder().build());
+
+        SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(requireContext());
+        Typeface monospaceFont = FontManager.getMonospaceFont(requireContext(), prefs);
+        CodeViewUtils.applyDefaults(monospaceFont, binding.codeView);
+
+        StringBuilder builder = new StringBuilder();
+        InputStream inputStream = getResources().openRawResource(R.raw.text_retrofit_java);
+        try (BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream))) {
+            String line;
+            while ((line = reader.readLine()) != null) {
+                builder.append(line).append('\n');
+            }
+            binding.codeView.setText(builder.toString());
+            CodeHighlighter.applyJavaTheme(binding.codeView);
+        } catch (IOException e) {
+            Log.e("RetrofitTabCode", "Error reading code", e);
+        }
+        return binding.getRoot();
+    }
+}

app/src/main/java/com/d4rk/androidtutorials/java/ui/screens/android/lessons/networking/retrofit/tabs/RetrofitTabLayoutFragment.java

@@ -0,0 +1,58 @@
+package com.d4rk.androidtutorials.java.ui.screens.android.lessons.networking.retrofit.tabs;
+
+import android.content.SharedPreferences;
+import android.graphics.Typeface;
+import android.os.Bundle;
+import android.util.Log;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+
+import androidx.annotation.NonNull;
+import androidx.fragment.app.Fragment;
+import androidx.preference.PreferenceManager;
+
+import com.d4rk.androidtutorials.java.R;
+import com.d4rk.androidtutorials.java.databinding.FragmentLayoutBinding;
+import com.d4rk.androidtutorials.java.utils.CodeHighlighter;
+import com.d4rk.androidtutorials.java.utils.CodeViewUtils;
+import com.d4rk.androidtutorials.java.utils.FontManager;
+import com.google.android.gms.ads.AdRequest;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+
+import me.zhanghai.android.fastscroll.FastScrollerBuilder;
+
+/**
+ * Shows the XML layout for the Retrofit example.
+ */
+public class RetrofitTabLayoutFragment extends Fragment {
+
+    @Override
+    public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
+        FragmentLayoutBinding binding = FragmentLayoutBinding.inflate(inflater, container, false);
+        new FastScrollerBuilder(binding.scrollView).useMd2Style().build();
+        binding.adView.loadAd(new AdRequest.Builder().build());
+
+        SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(requireContext());
+        Typeface monospaceFont = FontManager.getMonospaceFont(requireContext(), prefs);
+        CodeViewUtils.applyDefaults(monospaceFont, binding.codeView);
+
+        StringBuilder builder = new StringBuilder();
+        InputStream inputStream = getResources().openRawResource(R.raw.text_retrofit_xml);
+        try (BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream))) {
+            String line;
+            while ((line = reader.readLine()) != null) {
+                builder.append(line).append('\n');
+            }
+            binding.codeView.setText(builder.toString());
+            CodeHighlighter.applyXmlTheme(binding.codeView);
+        } catch (IOException e) {
+            Log.e("RetrofitTabLayout", "Error reading layout", e);
+        }
+        return binding.getRoot();
+    }
+}

app/src/main/java/com/d4rk/androidtutorials/java/ui/screens/android/repository/LessonRepository.java

@@ -38,6 +38,8 @@ public com.d4rk.androidtutorials.java.data.repository.LessonRepository.Lesson ge
                     new com.d4rk.androidtutorials.java.data.repository.LessonRepository.Lesson(R.string.grid_view, R.raw.text_grid_view_java, R.raw.text_grid_view_xml);
             case "WebView" ->
                     new com.d4rk.androidtutorials.java.data.repository.LessonRepository.Lesson(R.string.web_view, R.raw.text_webview_java, R.raw.text_webview_xml);
+            case "Retrofit" ->
+                    new com.d4rk.androidtutorials.java.data.repository.LessonRepository.Lesson(R.string.retrofit, R.raw.text_retrofit_java, R.raw.text_retrofit_xml);
             case "BottomNavigation" ->
                     new com.d4rk.androidtutorials.java.data.repository.LessonRepository.Lesson(R.string.bottom_navigation, R.raw.text_bottom_navigation_java, R.raw.text_bottom_navigation_xml);
             case "NavigationDrawer" ->

app/src/main/res/drawable-anydpi/ic_category_network_tinted.xml

@@ -0,0 +1,9 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="24"
+    android:viewportHeight="24">
+  <path
+      android:fillColor="?attr/colorSecondary"
+      android:pathData="M6.5,20Q5.88,20 5.44,19.56Q5,19.12 5,18.5L5,15.5Q5,14.88 5.44,14.44Q5.88,14 6.5,14Q7.12,14 7.56,14.44Q8,14.88 8,15.5L8,18.5Q8,19.12 7.56,19.56Q7.12,20 6.5,20ZM12.5,20Q11.88,20 11.44,19.56Q11,19.12 11,18.5L11,10.5Q11,9.88 11.44,9.44Q11.88,9 12.5,9Q13.12,9 13.56,9.44Q14,9.88 14,10.5L14,18.5Q14,19.12 13.56,19.56Q13.12,20 12.5,20ZM18.5,20Q17.88,20 17.44,19.56Q17,19.12 17,18.5L17,5.5Q17,4.88 17.44,4.44Q17.88,4 18.5,4Q19.12,4 19.56,4.44Q20,4.88 20,5.5L20,18.5Q20,19.12 19.56,19.56Q19.12,20 18.5,20Z"/>
+</vector>

app/src/main/res/layout/activity_retrofit.xml

@@ -0,0 +1,53 @@
+<?xml version="1.0" encoding="utf-8"?>
+<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto"
+    android:id="@+id/constraintLayout"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent">
+
+    <com.google.android.material.textview.MaterialTextView
+        android:id="@+id/textViewSummary"
+        android:layout_width="0dp"
+        android:layout_height="wrap_content"
+        android:padding="16dp"
+        android:text="@string/summary_retrofit"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toTopOf="parent" />
+
+    <com.google.android.material.button.MaterialButton
+        android:id="@+id/buttonFetch"
+        style="@style/Widget.Material3.Button.ElevatedButton"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_marginTop="16dp"
+        android:text="@string/fetch_data"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toBottomOf="@id/textViewSummary" />
+
+    <com.google.android.material.textview.MaterialTextView
+        android:id="@+id/textViewResult"
+        android:layout_width="0dp"
+        android:layout_height="wrap_content"
+        android:layout_marginTop="16dp"
+        android:padding="16dp"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toBottomOf="@id/buttonFetch" />
+
+    <com.google.android.material.floatingactionbutton.ExtendedFloatingActionButton
+        android:id="@+id/floating_button_show_syntax"
+        style="@style/Widget.Material3.ExtendedFloatingActionButton.Icon.Surface"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_margin="24dp"
+        android:contentDescription="@string/tooltip_show_java_code_snippet"
+        android:text="@string/show_code"
+        android:textSize="14sp"
+        android:tooltipText="@string/tooltip_show_java_code_snippet"
+        app:icon="@drawable/ic_code"
+        app:layout_constraintBottom_toBottomOf="parent"
+        app:layout_constraintEnd_toEndOf="parent" />
+
+</androidx.constraintlayout.widget.ConstraintLayout>