Теперь приложение умеет получать и парсить ответы от сервера. Недоделанный TreeView для первого уровня ветви.

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

@@ -1,7 +1,12 @@
 package ru.volgorobot.vrcatalog;
 
+import android.app.Fragment;
+import android.app.FragmentManager;
+import android.app.FragmentTransaction;
 import android.content.Intent;
+import android.content.SharedPreferences;
 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;
@@ -30,6 +35,17 @@ public class MainActivity extends AppCompatActivity
 
         NavigationView navigationView = findViewById(R.id.nav_view);
         navigationView.setNavigationItemSelectedListener(this);
+        SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);
+        String baseURL = sharedPreferences.getString("addressOfServer", "");
+
+        FragmentManager fragmentManager = getFragmentManager();
+        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
+        TreeViewFragment treeViewFragment = new TreeViewFragment();
+
+        Bundle bundle = new Bundle();
+        bundle.putString("baseURL", baseURL);
+        treeViewFragment.setArguments(bundle);
+        fragmentTransaction.add(R.id.fragment_container, treeViewFragment).commit();
     }
 
     @Override

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

@@ -3,16 +3,83 @@ package ru.volgorobot.vrcatalog;
 import android.app.Fragment;
 import android.os.Bundle;
 import android.support.annotation.Nullable;
+import android.util.Log;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+import android.widget.Toast;
 
 import com.unnamed.b.atv.model.TreeNode;
 import com.unnamed.b.atv.view.AndroidTreeView;
+import com.unnamed.b.atv.view.TreeNodeWrapperView;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import retrofit2.Call;
+import retrofit2.Callback;
+import retrofit2.Response;
+import ru.volgorobot.vrcatalog.api.Controller;
+import ru.volgorobot.vrcatalog.api.VRApi;
+import ru.volgorobot.vrcatalog.model.FirstLevelModel;
 
 public class TreeViewFragment extends Fragment {
 
     private AndroidTreeView treeView;
+    private VRApi vrApi;
+    private List<FirstLevelModel> firstLevelObjects = new ArrayList<>();
+    private List<TreeNode> firstLevelNodes = new ArrayList<>();
 
     @Override
     public void onCreate(@Nullable Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
+
+
+
+        Bundle bundle = this.getArguments();
+        String baseURL = bundle.getString("baseURL");
+        vrApi = Controller.getApi(baseURL, getActivity());
+
+        vrApi.getFirstLevel().enqueue(new Callback<List<FirstLevelModel>>() {
+            @Override
+            public void onResponse(Call<List<FirstLevelModel>> call, Response<List<FirstLevelModel>> response) {
+                if(response != null) {
+                    try {
+                        firstLevelObjects.addAll(response.body());
+                    } catch(Exception e) {
+                        Log.e("ERROR", "Answer of server is wrong!");
+                        Log.e("ERROR", response.message());
+                    }
+                    fillFirstLevel();
+                } else {
+                    Log.e("ERROR", "Что-то пошло не так...");
+                }
+
+            }
+
+            @Override
+            public void onFailure(Call<List<FirstLevelModel>> call, Throwable t) {
+                Log.e("ERROR", "getFirstLevel() failed!");
+            }
+        });
+
+    }
+
+    @Nullable
+    @Override
+    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, Bundle savedInstanceState) {
+        View rootView = inflater.inflate(R.layout.fragment_default, null, false);
+        TreeNodeWrapperView containerView = rootView.findViewById(R.id.treeViewContainer);
+        TreeNode root = TreeNode.root();
+        root.addChildren(firstLevelNodes);
+        treeView = new AndroidTreeView(getActivity(), root);
+        //containerView.insertNodeView(treeView);
+        return rootView;
+    }
+
+    private void fillFirstLevel() {
+        for (int i = 0; i < firstLevelObjects.size(); i++) {
+            firstLevelNodes.add(new TreeNode(firstLevelObjects.get(i).getName()));
+        }
     }
 }

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

@@ -0,0 +1,40 @@
+package ru.volgorobot.vrcatalog.api;
+
+import android.content.Context;
+import android.widget.Toast;
+
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+
+import retrofit2.Retrofit;
+import retrofit2.converter.gson.GsonConverterFactory;
+
+public class Controller {
+    private static String baseURL;
+    private static Context context;
+    private static Retrofit retrofit;
+
+
+    public static VRApi getApi(String baseURL1, Context context1) {
+        baseURL = baseURL1;
+        context = context1;
+        Gson gson = new GsonBuilder()
+                .setLenient()
+                .create();
+
+        buildRetrofitObject(gson);
+
+        return retrofit.create(VRApi.class);
+    }
+
+    private static void buildRetrofitObject(Gson gson) {
+        try {
+            retrofit = new Retrofit.Builder()
+                    .baseUrl(baseURL)
+                    .addConverterFactory(GsonConverterFactory.create(gson))
+                    .build();
+        } catch(Exception e) {
+            Toast.makeText(context, "Вы ввели неверный URL. Пример: http://example", Toast.LENGTH_LONG).show();
+        }
+    }
+}

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

@@ -0,0 +1,13 @@
+package ru.volgorobot.vrcatalog.api;
+
+import java.util.List;
+
+import retrofit2.Call;
+import retrofit2.http.GET;
+import ru.volgorobot.vrcatalog.model.FirstLevelModel;
+
+public interface VRApi {
+
+    @GET("/API/Api.php?action=getFirstLevel")
+    Call<List<FirstLevelModel>> getFirstLevel();
+}

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

@@ -8,4 +8,9 @@
     tools:context=".MainActivity"
     tools:showIn="@layout/app_bar_main">
 
+    <RelativeLayout
+        android:layout_width="match_parent"
+        android:layout_height="match_parent"
+        android:id="@+id/fragment_container"></RelativeLayout>
+
 </android.support.constraint.ConstraintLayout>

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

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
-<android.support.v7.widget.LinearLayoutCompat
+<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
-    xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent"
+    android:layout_width="match_parent"
-    android:layout_height="match_parent">
+    android:layout_height="match_parent"
-
+    android:id="@+id/treeViewContainer">
-</android.support.v7.widget.LinearLayoutCompat>
+</FrameLayout>

app/src/main/res/xml/activity_settings.xml

@@ -3,5 +3,6 @@
     <EditTextPreference
         android:key="addressOfServer"
         android:title="Адрес PHP скрипта-посредника"
-        android:summary="PHP скрипт-посредник необходим для доступа к БД деталей" />
+        android:summary="PHP скрипт-посредник необходим для доступа к БД деталей"
+        android:defaultValue="http://example.com"/>
 </PreferenceScreen>