The application architecture was refactored (the application now uses the MVP architectural pattern), and dynamic loading of all levels of the tree is implemented.

.idea/misc.xml

@@ -29,7 +29,7 @@
       </value>
     </option>
   </component>
-  <component name="ProjectRootManager" version="2" languageLevel="JDK_1_7" project-jdk-name="1.8" project-jdk-type="JavaSDK">
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_1_8" project-jdk-name="1.8" project-jdk-type="JavaSDK">
     <output url="file://$PROJECT_DIR$/build/classes" />
   </component>
   <component name="ProjectType">

app/build.gradle

@@ -10,6 +10,10 @@ android {
         versionName "1.0"
         testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
     }
+    compileOptions {
+        sourceCompatibility JavaVersion.VERSION_1_8
+        targetCompatibility JavaVersion.VERSION_1_8
+    }
     buildTypes {
         release {
             minifyEnabled false
@@ -24,6 +28,7 @@ dependencies {
     implementation 'com.android.support:appcompat-v7:27.1.1'
     implementation 'com.android.support:design:27.1.1'
     implementation 'com.android.support.constraint:constraint-layout:1.1.3'
+    implementation 'com.github.msteinbeck:sig4j:1.0.1'
     implementation 'me.texy.treeview:treeview_lib:1.0.4'
     implementation 'com.google.code.gson:gson:2.8.2'
     implementation 'com.squareup.retrofit2:retrofit:2.1.0'

app/src/main/AndroidManifest.xml

@@ -12,7 +12,7 @@
         android:supportsRtl="true"
         android:theme="@style/AppTheme">
         <activity
-            android:name=".MainActivity"
+            android:name=".view.MainActivity"
             android:label="@string/app_name"
             android:theme="@style/AppTheme.NoActionBar">
             <intent-filter>
@@ -21,8 +21,8 @@
                 <category android:name="android.intent.category.LAUNCHER" />
             </intent-filter>
         </activity>
-        <activity android:name=".SettingsActivity" />
+        <activity android:name=".view.SettingsActivity" />
-        <activity android:name=".AboutActivity"></activity>
+        <activity android:name=".view.AboutActivity"></activity>
     </application>
 
 </manifest>

app/src/main/java/ru/volgorobot/vrcatalog/MainActivity.java

@@ -1,247 +0,0 @@
-package ru.volgorobot.vrcatalog;
-
-import android.content.AsyncQueryHandler;
-import android.content.Intent;
-import android.content.SharedPreferences;
-import android.os.AsyncTask;
-import android.os.Bundle;
-import android.preference.PreferenceManager;
-import android.support.design.widget.NavigationView;
-import android.support.v4.view.GravityCompat;
-import android.support.v4.widget.DrawerLayout;
-import android.support.v4.widget.SwipeRefreshLayout;
-import android.support.v7.app.ActionBarDrawerToggle;
-import android.support.v7.app.AppCompatActivity;
-import android.support.v7.widget.Toolbar;
-import android.util.Log;
-import android.view.MenuItem;
-import android.view.View;
-import android.view.ViewGroup;
-import android.widget.Toast;
-
-import java.io.IOException;
-import java.util.ArrayList;
-import java.util.List;
-
-import me.texy.treeview.TreeNode;
-import me.texy.treeview.TreeView;
-import retrofit2.Call;
-import retrofit2.Callback;
-import retrofit2.Response;
-import ru.volgorobot.vrcatalog.additional.NodeViewFactory;
-import ru.volgorobot.vrcatalog.api.Controller;
-import ru.volgorobot.vrcatalog.api.VRApi;
-import ru.volgorobot.vrcatalog.model.FirstLevelModel;
-import ru.volgorobot.vrcatalog.model.SecondLevelModel;
-import ru.volgorobot.vrcatalog.model.ThirdLevelModel;
-
-public class MainActivity extends AppCompatActivity
-        implements NavigationView.OnNavigationItemSelectedListener, SwipeRefreshLayout.OnRefreshListener {
-
-    private TreeView treeView;
-    private VRApi vrApi;
-    private List<FirstLevelModel> firstLevelObjects = new ArrayList<>();
-    private List<TreeNode> firstLevelNodes = new ArrayList<>();
-    private List<SecondLevelModel> secondLevelObjects = new ArrayList<>();
-    private List<ThirdLevelModel> thirdLevelObjects = new ArrayList<>();
-
-    private TreeNode rootNode = TreeNode.root();
-    private SwipeRefreshLayout mSwipeRefreshLayout;
-
-    @Override
-    protected void onCreate(Bundle savedInstanceState) {
-        super.onCreate(savedInstanceState);
-        setContentView(R.layout.activity_main);
-        Toolbar toolbar = findViewById(R.id.toolbar);
-        setSupportActionBar(toolbar);
-
-
-        DrawerLayout drawer = findViewById(R.id.drawer_layout);
-        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
-                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
-        drawer.addDrawerListener(toggle);
-        toggle.syncState();
-
-        NavigationView navigationView = findViewById(R.id.nav_view);
-        navigationView.setNavigationItemSelectedListener(this);
-
-        mSwipeRefreshLayout = (SwipeRefreshLayout) findViewById(R.id.swipeRefreshLayout);
-        mSwipeRefreshLayout.setOnRefreshListener(MainActivity.this);
-        mSwipeRefreshLayout.setColorSchemeResources(R.color.colorPrimary);
-
-        try {
-            getTreeData(false);
-        } catch (IllegalStateException e) {
-            //
-        }
-        treeView = new TreeView(rootNode, MainActivity.this, new NodeViewFactory());
-        ((ViewGroup) findViewById(R.id.treeViewContainer)).addView(treeView.getView());
-    }
-
-    @Override
-    public void onBackPressed() {
-        DrawerLayout drawer = findViewById(R.id.drawer_layout);
-        if (drawer.isDrawerOpen(GravityCompat.START)) {
-            drawer.closeDrawer(GravityCompat.START);
-        } else {
-            super.onBackPressed();
-        }
-    }
-
-
-    @Override
-    public boolean onOptionsItemSelected(MenuItem item) {
-        // Handle action bar item clicks here. The action bar will
-        // automatically handle clicks on the Home/Up button, so long
-        // as you specify a parent activity in AndroidManifest.xml.
-
-        return super.onOptionsItemSelected(item);
-    }
-
-    @SuppressWarnings("StatementWithEmptyBody")
-    @Override
-    public boolean onNavigationItemSelected(MenuItem item) {
-        // Handle navigation view item clicks here.
-        int id = item.getItemId();
-        NavigationView navView = findViewById(R.id.nav_view);
-
-        if (id == R.id.nav_settings) {
-            startActivity(new Intent(this, SettingsActivity.class));
-
-        } else if (id == R.id.nav_about) {
-            startActivity(new Intent(this, AboutActivity.class));
-        }
-
-        DrawerLayout drawer = findViewById(R.id.drawer_layout);
-        drawer.closeDrawer(GravityCompat.START);
-        return true;
-    }
-
-    private void fillRootNode() {
-        for (int i = 0; i < firstLevelObjects.size(); i++) {
-            firstLevelNodes.add(new TreeNode(firstLevelObjects.get(i).getName()));
-            firstLevelNodes.get(i).setLevel(0);
-            firstLevelNodes.get(i).setChildren(getSecondLevelNodesByParentID(firstLevelObjects.get(i).getID()));
-        }
-
-        rootNode.setChildren(firstLevelNodes);
-    }
-
-    private ArrayList<TreeNode> getSecondLevelNodesByParentID(int parentTypeID) {
-        ArrayList<SecondLevelModel> objects = new ArrayList<>();
-        for (int i = 0; i < secondLevelObjects.size(); i++) {
-            if(secondLevelObjects.get(i).getDetailTypeId() == parentTypeID) {
-                objects.add(secondLevelObjects.get(i));
-            }
-        }
-        ArrayList<TreeNode> nodes = new ArrayList<>();
-        for (int i = 0; i < objects.size(); i++) {
-            nodes.add(new TreeNode(objects.get(i).getName()));
-            nodes.get(i).setLevel(1);
-        }
-        return nodes;
-    }
-
-    private ArrayList<TreeNode> getThirdLevelNodesByParentName(String parentName) {
-        ArrayList<ThirdLevelModel> objects = new ArrayList<>();
-        for (int i = 0; i < thirdLevelObjects.size(); i++) {
-            if(thirdLevelObjects.get(i).getName().equals(parentName)) {
-                objects.add(thirdLevelObjects.get(i));
-            }
-        }
-        ArrayList<TreeNode> nodes = new ArrayList<>();
-        for (int i = 0; i < objects.size(); i++) {
-            nodes.add(new TreeNode(objects.get(i).getName()));
-            nodes.get(i).setLevel(2);
-        }
-        return nodes;
-    }
-
-    @Override
-    public void onRefresh() {
-        mSwipeRefreshLayout.setRefreshing(true);
-
-        try {
-            getTreeData(true);
-        } catch (IllegalStateException e) {
-            //
-        }
-    }
-
-    private void getTreeData(final boolean clean) throws IllegalStateException {
-        mSwipeRefreshLayout.setRefreshing(true);
-        if(clean) {
-            firstLevelNodes.removeAll(firstLevelNodes);
-            firstLevelObjects.removeAll(firstLevelObjects);
-            secondLevelObjects.removeAll(secondLevelObjects);
-        }
-        SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);
-        String baseURL = sharedPreferences.getString("addressOfServer", "");
-
-        try {
-            vrApi = Controller.getApi(baseURL, this);
-        } catch(IllegalStateException e) {
-            throw new IllegalStateException();
-        }
-        class GetTreeData extends AsyncTask<Void, Void, Integer> {
-            @Override
-            protected Integer doInBackground(Void... voids) {
-                try {
-                    Response<List<FirstLevelModel>> firstLevelResponse = vrApi.getFirstLevel().execute();
-                    if(firstLevelResponse.isSuccessful()) {
-                        firstLevelObjects.addAll(firstLevelResponse.body());
-                        for (int i = 0; i < firstLevelObjects.size(); i++) {
-                            Response<List<SecondLevelModel>> secondLevelResponse = vrApi.getSecondLevel(firstLevelObjects.get(i).getID()).execute();
-                            if(secondLevelResponse.isSuccessful()) {
-                                secondLevelObjects.addAll(secondLevelResponse.body());
-                            } else {
-                                return 2;
-                            }
-                        }
-                    } else {
-                        return 2;
-                    }
-                } catch (Exception e) {
-                    return 1;
-                }
-                return 0;
-            }
-
-            @Override
-            protected void onPostExecute(Integer integer) {
-                super.onPostExecute(integer);
-                if(integer == 0) {
-                    fillRootNode();
-                    treeView.refreshTreeView();
-                    mSwipeRefreshLayout.setRefreshing(false);
-                } else if(integer == 1) {
-                    onFailureAnswer(1);
-                } else if(integer == 2) {
-                    onFailureAnswer(2);
-                }
-
-            }
-        }
-        new GetTreeData().execute();
-    }
-
-    private void onFailureAnswer(int errorCode) {
-        switch (errorCode) {
-            case 1: {
-                Toast.makeText(MainActivity.this, "Ошибка сети. Проверьте подключение к сети или данные подключения к API!", Toast.LENGTH_LONG).show();
-                Log.e("VRCatalog", "Network Error! Re-check your connection credentials or network settings! Technical info: null");
-                mSwipeRefreshLayout.setRefreshing(false);
-                break;
-            }
-            case 2: {
-                Toast.makeText(MainActivity.this, "Ответ от сервера неверен! Перепроверьте данные подключения!", Toast.LENGTH_LONG).show();
-                Log.e("VRCatalog", "Answer of server is wrong! Re-check your connection credentials! Technical info: null");
-                mSwipeRefreshLayout.setRefreshing(false);
-                break;
-            }
-        }
-    }
-
-}
-
-

app/src/main/java/ru/volgorobot/vrcatalog/MainContract.java

@@ -0,0 +1,32 @@
+package ru.volgorobot.vrcatalog;
+
+import android.widget.ImageView;
+
+import com.github.msteinbeck.sig4j.signal.Signal1;
+
+import java.util.ArrayList;
+
+import ru.volgorobot.vrcatalog.model.FirstLevelModel;
+import ru.volgorobot.vrcatalog.model.SecondLevelModel;
+import ru.volgorobot.vrcatalog.model.ThirdLevelModel;
+
+public interface MainContract {
+    interface MainActivityView {
+        void swipeLayoutSetRefreshing(boolean state);
+        void buildFirstLevelTree(ArrayList<FirstLevelModel> firstLevelModels);
+        void onFailureAnswer(int errorCode);
+        void refreshTree();
+    }
+
+    interface Presenter {
+        void getFirstLevel();
+        void failureAnswerSlot(int errorCode);
+    }
+
+    interface MainModel {
+        Signal1<Integer> errorSignal = new Signal1<>();
+        ArrayList<FirstLevelModel> getFirstLevel();
+        ArrayList<SecondLevelModel> getSecondLevelByParentID(int parentID);
+        ArrayList<ThirdLevelModel> getThirdLevelByParentID(int parentID);
+    }
+}

app/src/main/java/ru/volgorobot/vrcatalog/MainPresenter.java

@@ -0,0 +1,59 @@
+package ru.volgorobot.vrcatalog;
+
+import android.content.Context;
+import android.os.AsyncTask;
+
+import java.util.ArrayList;
+
+import ru.volgorobot.vrcatalog.model.CoreModel;
+import ru.volgorobot.vrcatalog.model.FirstLevelModel;
+
+public class MainPresenter implements MainContract.Presenter {
+    private MainContract.MainActivityView mView;
+    private MainContract.MainModel coreModel;
+
+    public MainPresenter(MainContract.MainActivityView mainActivityView, Context context) {
+        this.mView = mainActivityView;
+        try {
+            this.coreModel = new CoreModel(context);
+        } catch (IllegalStateException e) {
+            mView.onFailureAnswer(3);
+        }
+        coreModel.errorSignal.connect(this::failureAnswerSlot);
+    }
+
+    @Override
+    public void getFirstLevel() {
+        new AsyncTask<Void, Void, ArrayList<FirstLevelModel>>() {
+            @Override
+            protected ArrayList<FirstLevelModel> doInBackground(Void... voids) {
+                ArrayList<FirstLevelModel> firstLevelModels = coreModel.getFirstLevel();
+                return firstLevelModels;
+            }
+
+            @Override
+            protected void onPostExecute(ArrayList<FirstLevelModel> firstLevelModels) {
+                mView.buildFirstLevelTree(firstLevelModels);
+            }
+        }.execute();
+        mView.swipeLayoutSetRefreshing(false);
+    }
+
+    @Override
+    public void failureAnswerSlot(int errorCode) {
+        switch (errorCode) {
+            case 1: {
+                mView.onFailureAnswer(1);
+                break;
+            }
+            case 2: {
+                mView.onFailureAnswer(2);
+                break;
+            }
+            case 3: {
+                mView.onFailureAnswer(3);
+                break;
+            }
+        }
+    }
+}

app/src/main/java/ru/volgorobot/vrcatalog/additional/NodeViewFactory.java

@@ -1,21 +1,31 @@
 package ru.volgorobot.vrcatalog.additional;
 
+import android.content.Context;
 import android.view.View;
 
 import me.texy.treeview.base.BaseNodeViewBinder;
 import me.texy.treeview.base.BaseNodeViewFactory;
+import ru.volgorobot.vrcatalog.MainContract;
 import ru.volgorobot.vrcatalog.nodeViewBinders.FirstLevelNodeViewBinder;
 import ru.volgorobot.vrcatalog.nodeViewBinders.SecondLevelNodeViewBinder;
 import ru.volgorobot.vrcatalog.nodeViewBinders.ThirdLevelNodeViewBinder;
 
 public class NodeViewFactory extends BaseNodeViewFactory {
+    MainContract.MainActivityView mView;
+    Context context;
+
+    public NodeViewFactory(Context context, MainContract.MainActivityView mView) {
+        this.mView = mView;
+        this.context = context;
+    }
+
     @Override
     public BaseNodeViewBinder getNodeViewBinder(View view, int level) {
         switch (level) {
             case 0:
-                return new FirstLevelNodeViewBinder(view);
+                return new FirstLevelNodeViewBinder(view, context, mView);
             case 1:
-                return new SecondLevelNodeViewBinder(view);
+                return new SecondLevelNodeViewBinder(view, context, mView);
             case 2:
                 return new ThirdLevelNodeViewBinder(view);
             default:

app/src/main/java/ru/volgorobot/vrcatalog/api/Controller.java

@@ -11,14 +11,12 @@ import retrofit2.converter.gson.GsonConverterFactory;
 
 public class Controller {
     private static String baseURL;
-    private static Context context;
     private static Retrofit retrofit;
     private static VRApi vrApi;
 
 
-    public static VRApi getApi(String baseURL1, Context context1) throws IllegalStateException {
+    public static VRApi getApi(String baseURL1) throws IllegalStateException {
         baseURL = baseURL1;
-        context = context1;
         Gson gson = new GsonBuilder()
                 .setLenient()
                 .create();
@@ -38,7 +36,6 @@ public class Controller {
                     .addConverterFactory(GsonConverterFactory.create(gson))
                     .build();
         } catch(Exception e) {
-            Toast.makeText(context, "Вы ввели неверный URL. Пример: http://example.ru", Toast.LENGTH_LONG).show();
             throw new IllegalStateException();
         }
     }

app/src/main/java/ru/volgorobot/vrcatalog/model/CoreModel.java

@@ -0,0 +1,80 @@
+package ru.volgorobot.vrcatalog.model;
+
+import android.content.Context;
+import android.content.SharedPreferences;
+import android.preference.PreferenceManager;
+import com.github.msteinbeck.sig4j.signal.Signal1;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+
+import retrofit2.Response;
+import ru.volgorobot.vrcatalog.MainContract;
+import ru.volgorobot.vrcatalog.api.Controller;
+import ru.volgorobot.vrcatalog.api.VRApi;
+
+public class CoreModel implements MainContract.MainModel {
+    private Context context;
+    private VRApi vrApi;
+    public final Signal1<Integer> errorSignal = new Signal1<>();
+
+    public CoreModel(Context context) throws IllegalStateException {
+        this.context = context;
+        SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(context);
+        String baseURL = sharedPreferences.getString("addressOfServer", "");
+        try {
+            vrApi = Controller.getApi(baseURL);
+        } catch(IllegalStateException e) {
+            throw new IllegalStateException();
+        }
+    }
+
+    @Override
+    public ArrayList<FirstLevelModel> getFirstLevel() {
+        final ArrayList<FirstLevelModel> firstLevelModels = new ArrayList<>();
+        try {
+            Response<List<FirstLevelModel>> response = vrApi.getFirstLevel().execute();
+            if(response.isSuccessful()) {
+                firstLevelModels.addAll(response.body());
+            } else {
+                errorSignal.emit(2);
+            }
+        } catch (IOException e) {
+            errorSignal.emit(1);
+        }
+        return firstLevelModels;
+    }
+
+    @Override
+    public ArrayList<SecondLevelModel> getSecondLevelByParentID(int parentID) {
+        final ArrayList<SecondLevelModel> secondLevelModels = new ArrayList<>();
+        try {
+            Response<List<SecondLevelModel>> response = vrApi.getSecondLevel(parentID).execute();
+            if(response.isSuccessful()) {
+                secondLevelModels.addAll(response.body());
+            } else {
+                errorSignal.emit(2);
+            }
+        } catch (IOException e) {
+            errorSignal.emit(1);
+        }
+        return secondLevelModels;
+    }
+
+    @Override
+    public ArrayList<ThirdLevelModel> getThirdLevelByParentID(int parentID) {
+        final ArrayList<ThirdLevelModel> thirdLevelModels = new ArrayList<>();
+        try {
+            Response<List<ThirdLevelModel>> response = vrApi.getDetails(parentID).execute();
+            if(response.isSuccessful()) {
+                thirdLevelModels.addAll(response.body());
+            } else {
+                errorSignal.emit(2);
+            }
+        } catch (IOException e) {
+            errorSignal.emit(1);
+        }
+        return thirdLevelModels;
+    }
+}

app/src/main/java/ru/volgorobot/vrcatalog/model/FirstLevelModel.java

@@ -40,4 +40,7 @@ public class FirstLevelModel {
         this.iD = iD;
     }
 
+    public String toString() {
+        return name;
+    }
 }

app/src/main/java/ru/volgorobot/vrcatalog/model/SecondLevelModel.java

@@ -51,4 +51,7 @@ public class SecondLevelModel {
         this.name = name;
     }
 
+    public String toString() {
+        return name;
+    }
 }

app/src/main/java/ru/volgorobot/vrcatalog/model/ThirdLevelModel.java

@@ -59,4 +59,7 @@ public class ThirdLevelModel {
         this.name = name;
     }
 
+    public String toString() {
+        return name;
+    }
 }

app/src/main/java/ru/volgorobot/vrcatalog/nodeViewBinders/FirstLevelNodeViewBinder.java

@@ -1,21 +1,34 @@
 package ru.volgorobot.vrcatalog.nodeViewBinders;
 
+import android.content.Context;
+import android.os.AsyncTask;
 import android.view.View;
 import android.widget.ImageView;
 import android.widget.TextView;
 
+import java.util.ArrayList;
+
 import me.texy.treeview.TreeNode;
 import me.texy.treeview.base.BaseNodeViewBinder;
+import ru.volgorobot.vrcatalog.MainContract;
 import ru.volgorobot.vrcatalog.R;
+import ru.volgorobot.vrcatalog.model.CoreModel;
+import ru.volgorobot.vrcatalog.model.FirstLevelModel;
+import ru.volgorobot.vrcatalog.model.SecondLevelModel;
 
 public class FirstLevelNodeViewBinder extends BaseNodeViewBinder {
     TextView textView;
     ImageView imageView;
+    CoreModel coreModel;
+    MainContract.MainActivityView mView;
 
-    public FirstLevelNodeViewBinder(View itemView) {
+    public FirstLevelNodeViewBinder(View itemView, Context context, MainContract.MainActivityView mView) {
         super(itemView);
         textView = (TextView) itemView.findViewById(R.id.node_name_view);
         imageView = (ImageView) itemView.findViewById(R.id.arrow_img);
+        this.coreModel = new CoreModel(context);
+        this.mView = mView;
+        coreModel.errorSignal.connect(mView::onFailureAnswer);
     }
 
     @Override
@@ -31,7 +44,35 @@ public class FirstLevelNodeViewBinder extends BaseNodeViewBinder {
     @Override
     public void onNodeToggled(TreeNode treeNode, boolean expand) {
         if(expand) {
+            FirstLevelModel firstLevelModel = (FirstLevelModel) treeNode.getValue();
+            new AsyncTask<Void, Void, ArrayList<SecondLevelModel>>() {
+                @Override
+                protected void onPreExecute() {
+                    super.onPreExecute();
+                    mView.swipeLayoutSetRefreshing(true);
+                }
+
+                @Override
+                protected ArrayList<SecondLevelModel> doInBackground(Void... voids) {
+                    ArrayList<SecondLevelModel> secondLevelModels = coreModel.getSecondLevelByParentID(firstLevelModel.getID());
+                    return secondLevelModels;
+                }
+
+                @Override
+                protected void onPostExecute(ArrayList<SecondLevelModel> secondLevelModels) {
+                    super.onPostExecute(secondLevelModels);
+                    ArrayList<TreeNode> treeNodes = new ArrayList<>();
+                    for (int i = 0; i < secondLevelModels.size(); i++) {
+                        TreeNode treeNode1 = new TreeNode(secondLevelModels.get(i));
+                        treeNode1.setLevel(1);
+                        treeNodes.add(treeNode1);
+                    }
+                    treeNode.setChildren(treeNodes);
+                    mView.refreshTree();
+                    mView.swipeLayoutSetRefreshing(false);
                     imageView.animate().rotation(90).setDuration(200).start();
+                }
+            }.execute();
         } else {
             imageView.animate().rotation(0).setDuration(200).start();
         }

app/src/main/java/ru/volgorobot/vrcatalog/nodeViewBinders/SecondLevelNodeViewBinder.java

@@ -1,21 +1,35 @@
 package ru.volgorobot.vrcatalog.nodeViewBinders;
 
+import android.content.Context;
+import android.os.AsyncTask;
 import android.view.View;
 import android.widget.ImageView;
 import android.widget.TextView;
 
+import java.util.ArrayList;
+
 import me.texy.treeview.TreeNode;
 import me.texy.treeview.base.BaseNodeViewBinder;
+import ru.volgorobot.vrcatalog.MainContract;
 import ru.volgorobot.vrcatalog.R;
+import ru.volgorobot.vrcatalog.model.CoreModel;
+import ru.volgorobot.vrcatalog.model.SecondLevelModel;
+import ru.volgorobot.vrcatalog.model.ThirdLevelModel;
 
 public class SecondLevelNodeViewBinder extends BaseNodeViewBinder {
     TextView textView;
     ImageView imageView;
+    MainContract.MainModel coreModel;
+    MainContract.MainActivityView mView;
 
-    public SecondLevelNodeViewBinder(View itemView) {
+
+    public SecondLevelNodeViewBinder(View itemView, Context context, MainContract.MainActivityView mView) {
         super(itemView);
         textView = (TextView) itemView.findViewById(R.id.node_name_view);
         imageView = (ImageView) itemView.findViewById(R.id.arrow_img);
+        this.coreModel = new CoreModel(context);
+        this.mView = mView;
+        coreModel.errorSignal.connect(mView::onFailureAnswer);
     }
 
     @Override
@@ -32,7 +46,35 @@ public class SecondLevelNodeViewBinder extends BaseNodeViewBinder {
     @Override
     public void onNodeToggled(TreeNode treeNode, boolean expand) {
         if(expand) {
+            SecondLevelModel secondLevelModel = (SecondLevelModel) treeNode.getValue();
+            new AsyncTask<Void, Void, ArrayList<ThirdLevelModel>>() {
+                @Override
+                protected void onPreExecute() {
+                    super.onPreExecute();
+                    mView.swipeLayoutSetRefreshing(true);
+                }
+
+                @Override
+                protected ArrayList<ThirdLevelModel> doInBackground(Void... voids) {
+                    ArrayList<ThirdLevelModel> thirdLevelModels = coreModel.getThirdLevelByParentID(secondLevelModel.getID());
+                    return thirdLevelModels;
+                }
+
+                @Override
+                protected void onPostExecute(ArrayList<ThirdLevelModel> thirdLevelModels) {
+                    super.onPostExecute(thirdLevelModels);
+                    ArrayList<TreeNode> treeNodes = new ArrayList<>();
+                    for (int i = 0; i < thirdLevelModels.size(); i++) {
+                        TreeNode treeNode1 = new TreeNode(thirdLevelModels.get(i));
+                        treeNode1.setLevel(2);
+                        treeNodes.add(treeNode1);
+                    }
+                    treeNode.setChildren(treeNodes);
+                    mView.refreshTree();
+                    mView.swipeLayoutSetRefreshing(false);
                     imageView.animate().rotation(90).setDuration(200).start();
+                }
+            }.execute();
         } else {
             imageView.animate().rotation(0).setDuration(200).start();
         }

app/src/main/java/ru/volgorobot/vrcatalog/view/AboutActivity.java

@@ -1,10 +1,12 @@
-package ru.volgorobot.vrcatalog;
+package ru.volgorobot.vrcatalog.view;
 
 import android.os.Bundle;
 import android.support.v7.app.AppCompatActivity;
 import android.view.Menu;
 import android.view.MenuItem;
 
+import ru.volgorobot.vrcatalog.R;
+
 public class AboutActivity extends AppCompatActivity {
 
     @Override

app/src/main/java/ru/volgorobot/vrcatalog/view/MainActivity.java

@@ -0,0 +1,156 @@
+package ru.volgorobot.vrcatalog.view;
+
+import android.content.Intent;
+import android.os.Bundle;
+import android.support.design.widget.NavigationView;
+import android.support.v4.view.GravityCompat;
+import android.support.v4.widget.DrawerLayout;
+import android.support.v4.widget.SwipeRefreshLayout;
+import android.support.v7.app.ActionBarDrawerToggle;
+import android.support.v7.app.AppCompatActivity;
+import android.support.v7.widget.DefaultItemAnimator;
+import android.support.v7.widget.Toolbar;
+import android.util.Log;
+import android.view.MenuItem;
+import android.view.ViewGroup;
+import android.widget.Toast;
+
+import java.util.ArrayList;
+
+import me.texy.treeview.TreeNode;
+import me.texy.treeview.TreeView;
+import ru.volgorobot.vrcatalog.MainContract;
+import ru.volgorobot.vrcatalog.MainPresenter;
+import ru.volgorobot.vrcatalog.R;
+import ru.volgorobot.vrcatalog.additional.NodeViewFactory;
+import ru.volgorobot.vrcatalog.model.FirstLevelModel;
+
+public class MainActivity extends AppCompatActivity
+        implements NavigationView.OnNavigationItemSelectedListener, SwipeRefreshLayout.OnRefreshListener, MainContract.MainActivityView {
+
+    private MainContract.Presenter mPresenter;
+    private TreeView treeView;
+    private TreeNode rootNode = TreeNode.root();
+    private SwipeRefreshLayout mSwipeRefreshLayout;
+
+    @Override
+    protected void onCreate(Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+        setContentView(R.layout.activity_main);
+        Toolbar toolbar = findViewById(R.id.toolbar);
+        setSupportActionBar(toolbar);
+
+        DrawerLayout drawer = findViewById(R.id.drawer_layout);
+        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
+                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
+        drawer.addDrawerListener(toggle);
+        toggle.syncState();
+
+        NavigationView navigationView = findViewById(R.id.nav_view);
+        navigationView.setNavigationItemSelectedListener(this);
+
+        mSwipeRefreshLayout = (SwipeRefreshLayout) findViewById(R.id.swipeRefreshLayout);
+        mSwipeRefreshLayout.setOnRefreshListener(MainActivity.this);
+        mSwipeRefreshLayout.setColorSchemeResources(R.color.colorPrimary);
+
+        mPresenter = new MainPresenter(this, MainActivity.this);
+
+        treeView = new TreeView(rootNode, MainActivity.this, new NodeViewFactory(MainActivity.this, this));
+        treeView.setItemAnimator(new DefaultItemAnimator());
+        ((ViewGroup) findViewById(R.id.treeViewContainer)).addView(treeView.getView());
+        mSwipeRefreshLayout.setRefreshing(true);
+        mPresenter.getFirstLevel();
+    }
+
+    @Override
+    public void onBackPressed() {
+        DrawerLayout drawer = findViewById(R.id.drawer_layout);
+        if (drawer.isDrawerOpen(GravityCompat.START)) {
+            drawer.closeDrawer(GravityCompat.START);
+        } else {
+            super.onBackPressed();
+        }
+    }
+
+
+    @Override
+    public boolean onOptionsItemSelected(MenuItem item) {
+        // Handle action bar item clicks here. The action bar will
+        // automatically handle clicks on the Home/Up button, so long
+        // as you specify a parent activity in AndroidManifest.xml.
+
+        return super.onOptionsItemSelected(item);
+    }
+
+    @SuppressWarnings("StatementWithEmptyBody")
+    @Override
+    public boolean onNavigationItemSelected(MenuItem item) {
+        // Handle navigation view item clicks here.
+        int id = item.getItemId();
+        NavigationView navView = findViewById(R.id.nav_view);
+
+        if (id == R.id.nav_settings) {
+            startActivity(new Intent(this, SettingsActivity.class));
+
+        } else if (id == R.id.nav_about) {
+            startActivity(new Intent(this, AboutActivity.class));
+        }
+
+        DrawerLayout drawer = findViewById(R.id.drawer_layout);
+        drawer.closeDrawer(GravityCompat.START);
+        return true;
+    }
+
+
+    @Override
+    public void onRefresh() {
+        mSwipeRefreshLayout.setRefreshing(true);
+        mPresenter.getFirstLevel();
+    }
+
+    public void onFailureAnswer(int errorCode) {
+        switch (errorCode) {
+            case 1: {
+                Toast.makeText(MainActivity.this, "Ошибка сети. Проверьте подключение к сети или данные подключения к API!", Toast.LENGTH_LONG).show();
+                Log.e("VRCatalog", "Network Error! Re-check your connection credentials or network settings! Technical info: null");
+                mSwipeRefreshLayout.setRefreshing(false);
+                break;
+            }
+            case 2: {
+                Toast.makeText(MainActivity.this, "Ответ от сервера неверен! Перепроверьте данные подключения!", Toast.LENGTH_LONG).show();
+                Log.e("VRCatalog", "Answer of server is wrong! Re-check your connection credentials! Technical info: null");
+                mSwipeRefreshLayout.setRefreshing(false);
+                break;
+            }
+            case 3: {
+                Toast.makeText(this, "Вы ввели неверный URL. Пример: http://example.ru", Toast.LENGTH_LONG).show();
+                mSwipeRefreshLayout.setRefreshing(false);
+                break;
+            }
+        }
+    }
+
+    @Override
+    public void swipeLayoutSetRefreshing(boolean state) {
+        mSwipeRefreshLayout.setRefreshing(state);
+    }
+
+    @Override
+    public void buildFirstLevelTree(ArrayList<FirstLevelModel> firstLevelModels) {
+        ArrayList<TreeNode> treeNodes = new ArrayList<>();
+        for (int i = 0; i < firstLevelModels.size(); i++) {
+            TreeNode treeNode = new TreeNode(firstLevelModels.get(i));
+            treeNode.setLevel(0);
+            treeNodes.add(treeNode);
+        }
+        rootNode.setChildren(treeNodes);
+        treeView.refreshTreeView();
+    }
+
+    @Override
+    public void refreshTree() {
+        treeView.refreshTreeView();
+    }
+}
+
+

app/src/main/java/ru/volgorobot/vrcatalog/view/SettingsActivity.java

@@ -1,8 +1,10 @@
-package ru.volgorobot.vrcatalog;
+package ru.volgorobot.vrcatalog.view;
 
 import android.os.Bundle;
 import android.view.Menu;
 import android.view.MenuItem;
+
+import ru.volgorobot.vrcatalog.R;
 import ru.volgorobot.vrcatalog.additional.AppCompatPreferenceActivity;
 
 public class SettingsActivity extends AppCompatPreferenceActivity {

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

@@ -5,7 +5,7 @@
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:gravity="center"
-    tools:context=".AboutActivity">
+    tools:context=".view.AboutActivity">
 
     <LinearLayout
         android:layout_width="wrap_content"

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

@@ -4,7 +4,7 @@
     xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
-    tools:context=".MainActivity">
+    tools:context=".view.MainActivity">
 
     <android.support.design.widget.AppBarLayout
         android:layout_width="match_parent"

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

@@ -5,7 +5,7 @@
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     app:layout_behavior="@string/appbar_scrolling_view_behavior"
-    tools:context=".MainActivity"
+    tools:context=".view.MainActivity"
     tools:showIn="@layout/app_bar_main"
     android:orientation="horizontal"
     android:id="@+id/swipeRefreshLayout">