Notifications list retained across orientation change.

Fixes #1198

app/build.gradle

@@ -49,7 +49,7 @@ dependencies {
     compile 'com.facebook.stetho:stetho:1.5.0'
 
     testCompile 'junit:junit:4.12'
-    testCompile 'org.robolectric:robolectric:3.4'
+    testCompile 'org.robolectric:robolectric:3.7.1'
 
     testCompile 'com.squareup.okhttp3:mockwebserver:3.8.1'
     androidTestCompile 'com.squareup.okhttp3:mockwebserver:3.8.1'
@@ -78,7 +78,7 @@ dependencies {
     androidTestImplementation "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version"
 
     testImplementation 'junit:junit:4.12'
-    testImplementation 'org.robolectric:robolectric:3.4'
+    testImplementation 'org.robolectric:robolectric:3.7.1'
     testImplementation 'org.mockito:mockito-all:1.10.19'
 
     testImplementation 'com.squareup.okhttp3:mockwebserver:3.8.1'

app/src/main/java/fr/free/nrw/commons/notification/NotificationActivity.java

@@ -1,6 +1,7 @@
 package fr.free.nrw.commons.notification;
 
 import android.annotation.SuppressLint;
+import android.app.FragmentManager;
 import android.content.Context;
 import android.content.Intent;
 import android.net.Uri;
@@ -10,7 +11,6 @@ import android.support.v7.widget.RecyclerView;
 
 import com.pedrogomez.renderers.RVRendererAdapter;
 
-import java.util.Collections;
 import java.util.List;
 
 import javax.inject.Inject;
@@ -35,12 +35,16 @@ public class NotificationActivity extends NavigationBaseActivity {
 
     @Inject NotificationController controller;
 
+    private static final String TAG_NOTIFICATION_WORKER_FRAGMENT = "NotificationWorkerFragment";
+    private NotificationWorkerFragment mNotificationWorkerFragment;
 
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_notification);
         ButterKnife.bind(this);
+        mNotificationWorkerFragment = (NotificationWorkerFragment) getFragmentManager()
+                                      .findFragmentByTag(TAG_NOTIFICATION_WORKER_FRAGMENT);
         initListView();
         initDrawer();
     }
@@ -55,14 +59,18 @@ public class NotificationActivity extends NavigationBaseActivity {
     private void addNotifications() {
         Timber.d("Add notifications");
 
+        if(mNotificationWorkerFragment == null){
             Observable.fromCallable(() -> controller.getNotifications())
                     .subscribeOn(Schedulers.io())
                     .observeOn(AndroidSchedulers.mainThread())
                     .subscribe(notificationList -> {
-                    Collections.reverse(notificationList);
                         Timber.d("Number of notifications is %d", notificationList.size());
+                        initializeAndSetNotificationList(notificationList);
                         setAdapter(notificationList);
                     }, throwable -> Timber.e(throwable, "Error occurred while loading notifications"));
+        } else {
+            setAdapter(mNotificationWorkerFragment.getNotificationList());
+        }
     }
 
     private void handleUrl(String url) {
@@ -85,4 +93,12 @@ public class NotificationActivity extends NavigationBaseActivity {
         Intent intent = new Intent(context, NotificationActivity.class);
         context.startActivity(intent);
     }
+
+    private void initializeAndSetNotificationList(List<Notification> notificationList){
+        FragmentManager fm = getFragmentManager();
+        mNotificationWorkerFragment = new NotificationWorkerFragment();
+        fm.beginTransaction().add(mNotificationWorkerFragment, TAG_NOTIFICATION_WORKER_FRAGMENT)
+                .commit();
+        mNotificationWorkerFragment.setNotificationList(notificationList);
+    }
 }

app/src/main/java/fr/free/nrw/commons/notification/NotificationWorkerFragment.java

@@ -0,0 +1,29 @@
+package fr.free.nrw.commons.notification;
+
+import android.app.Fragment;
+import android.os.Bundle;
+import android.support.annotation.Nullable;
+
+import java.util.List;
+
+/**
+ * Created by knightshade on 25/2/18.
+ */
+
+public class NotificationWorkerFragment extends Fragment {
+    private List<Notification> notificationList;
+
+    @Override
+    public void onCreate(@Nullable Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+        setRetainInstance(true);
+    }
+
+    public void setNotificationList(List<Notification> notificationList){
+        this.notificationList = notificationList;
+    }
+
+    public List<Notification> getNotificationList(){
+        return notificationList;
+    }
+}