Restore theme after closing/reopening the app.

Fix:#505

Author: jainkuniya

app/src/main/java/com/zulip/android/ZulipApp.java

@@ -598,4 +598,15 @@ public void setMessageContentEditParams(int seconds, boolean param) {
             }
         }
     }
+
+    /**
+     * Update preferred theme
+     * @param b true if night theme is preferred
+     */
+    public void makeNightThemeDefault(boolean nightTheme) {
+        SharedPreferences.Editor editor = getSettings().edit();
+
+        editor.putBoolean(Constants.NIGHT_THEME, nightTheme);
+        editor.apply();
+    }
 }

app/src/main/java/com/zulip/android/activities/ZulipActivity.java

@@ -354,6 +354,13 @@ protected void onCreate(Bundle savedInstanceState) {
             mMutedTopics = MutedTopics.get();
         }
 
+        boolean isCurrentThemeNight = (AppCompatDelegate.getDefaultNightMode() == AppCompatDelegate.MODE_NIGHT_YES);
+
+        //apply preferred theme
+       if (app.getSettings().getBoolean(Constants.NIGHT_THEME, false) && !isCurrentThemeNight) {
+            setNightMode(AppCompatDelegate.MODE_NIGHT_YES);
+        }
+
         this.logged_in = true;
         notifications = new Notifications(this);
         notifications.register();
@@ -386,7 +393,7 @@ public void onClick(View v) {
         sendBtn = (ImageView) findViewById(R.id.send_btn);
         addFileBtn = (ImageView) findViewById(R.id.add_btn);
         appBarLayout = (AppBarLayout) findViewById(R.id.appBarLayout);
-        boolean isCurrentThemeNight = (AppCompatDelegate.getDefaultNightMode() == AppCompatDelegate.MODE_NIGHT_YES);
+
         etSearchPeople = (EditText) findViewById(R.id.people_drawer_search);
         ivSearchPeopleCancel = (ImageView) findViewById(R.id.iv_people__search_cancel_button);
         onTextChangeOfPeopleSearchEditText();
@@ -2358,12 +2365,11 @@ public void onClick(
                     case -1:
                     case AppCompatDelegate.MODE_NIGHT_NO:
                         setNightMode(AppCompatDelegate.MODE_NIGHT_YES);
-                        break;
-                    case AppCompatDelegate.MODE_NIGHT_YES:
-                        setNightMode(AppCompatDelegate.MODE_NIGHT_NO);
+                        app.makeNightThemeDefault(true);
                         break;
                     default:
                         setNightMode(AppCompatDelegate.MODE_NIGHT_NO);
+                        app.makeNightThemeDefault(false);
                         break;
                 }
                 break;

app/src/main/java/com/zulip/android/util/Constants.java

@@ -27,4 +27,5 @@ public class Constants {
     //if two continuous messages are from same sender and time difference is less than this then hide it
     public static long HIDE_TIMESTAMP_THRESHOLD = 60 * 1000;// 1 minute
     public static String ACTION_MESSAGE_PUSH_NOTIFICATION = "ACTION_MESSAGE_PUSH_NOTIFICATION";
+    public static String NIGHT_THEME = "NIGHT_THEME";
 }