simplifies the initial theme setting (no need for "recreate()")

app/src/main/AndroidManifest.xml

@@ -17,6 +17,7 @@
     <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
 
     <application
+        android:name=".Trackbook"
         android:allowBackup="true"
         android:fullBackupContent="@xml/backupscheme"
         android:icon="@mipmap/ic_launcher"

app/src/main/java/org/y20k/trackbook/MainActivity.java

@@ -43,7 +43,6 @@ import android.support.v4.app.FragmentPagerAdapter;
 import android.support.v4.content.ContextCompat;
 import android.support.v4.content.LocalBroadcastManager;
 import android.support.v7.app.AppCompatActivity;
-import android.support.v7.app.AppCompatDelegate;
 import android.support.v7.widget.CardView;
 import android.util.SparseArray;
 import android.view.MenuItem;
@@ -94,12 +93,6 @@ public class MainActivity extends AppCompatActivity implements TrackbookKeys {
     private int mSelectedTab;
 
 
-    /* Sets day / night mode */
-    static {
-        AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_FOLLOW_SYSTEM);
-    }
-
-
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
@@ -461,6 +454,7 @@ public class MainActivity extends AppCompatActivity implements TrackbookKeys {
             public boolean onLongClick(View v) {
                 longPressFeedback(R.string.toastmessage_long_press_night_mode_switch);
                 NightModeHelper.switchToOpposite(MainActivity.this);
+                recreate();
                 return true;
             }
         });

app/src/main/java/org/y20k/trackbook/Trackbook.java

@@ -0,0 +1,58 @@
+/**
+ * Trackbook.java
+ * Implements the Trackbook class
+ * Trackbook starts up the app and sets up the basic theme (Day / Night)
+ *
+ * This file is part of
+ * TRACKBOOK - Movement Recorder for Android
+ *
+ * Copyright (c) 2016-18 - Y20K.org
+ * Licensed under the MIT-License
+ * http://opensource.org/licenses/MIT
+ *
+ * Trackbook uses osmdroid - OpenStreetMap-Tools for Android
+ * https://github.com/osmdroid/osmdroid
+ */
+
+package org.y20k.trackbook;
+
+import android.app.Application;
+import android.os.Build;
+import android.support.v7.app.AppCompatDelegate;
+
+import org.y20k.trackbook.helpers.LogHelper;
+import org.y20k.trackbook.helpers.NightModeHelper;
+
+
+/**
+ * Trackbook.class
+ */
+public class Trackbook extends Application {
+
+    /* Define log tag */
+    private static final String LOG_TAG = Trackbook.class.getSimpleName();
+
+
+    @Override
+    public void onCreate() {
+        super.onCreate();
+
+        // set Day / Night theme state
+        if (Build.VERSION.SDK_INT >= 28) {
+            // Android P might introduce a system wide theme option - in that case: follow system (28 = Build.VERSION_CODES.P)
+            AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_FOLLOW_SYSTEM);
+        } else {
+            // try t0 get last state the user chose
+            NightModeHelper.restoreSavedState(this);
+        }
+
+    }
+
+
+    @Override
+    public void onTerminate() {
+        super.onTerminate();
+        LogHelper.v(LOG_TAG, "Trackbook application terminated.");
+    }
+
+}

app/src/main/java/org/y20k/trackbook/helpers/NightModeHelper.java

@@ -16,14 +16,11 @@
 
 package org.y20k.trackbook.helpers;
 
-import android.app.Activity;
 import android.content.Context;
 import android.content.SharedPreferences;
 import android.content.res.Configuration;
-import android.os.Build;
 import android.preference.PreferenceManager;
 import android.support.v7.app.AppCompatDelegate;
-import android.view.View;
 
 
 /**
@@ -36,46 +33,43 @@ public final class NightModeHelper implements TrackbookKeys {
 
 
     /* Switches to opposite theme */
-    public static void switchToOpposite(Activity activity) {
-        switch (getCurrentNightModeState(activity)) {
+    public static void switchToOpposite(Context context) {
+        switch (getCurrentNightModeState(context)) {
             case Configuration.UI_MODE_NIGHT_NO:
                 // night mode is currently not active - turn on night mode
-                activateNightMode(activity);
+                activateNightMode(context);
                 break;
             case Configuration.UI_MODE_NIGHT_YES:
                 // night mode is currently active - turn off night mode
-                deactivateNightMode(activity);
+                deactivateNightMode(context);
                 break;
             case Configuration.UI_MODE_NIGHT_UNDEFINED:
                 // don't know what mode is active - turn off night mode
-                deactivateNightMode(activity);
+                deactivateNightMode(context);
                 break;
         }
-        activity.recreate(); // todo check if necessary
     }
 
 
     /* Sets night mode / dark theme */
-    public static void restoreSavedState(Activity activity) {
-        int savedNightModeState = loadNightModeState(activity);
-        int currentNightModeState = getCurrentNightModeState(activity);
-        LogHelper.i(LOG_TAG, "Saved state of Night Mode = " + savedNightModeState + " || current state of Night Mode = " + currentNightModeState + " || NO=16 & YES=32"); // todo remove
+    public static void restoreSavedState(Context context) {
+        int savedNightModeState = loadNightModeState(context);
+        int currentNightModeState = getCurrentNightModeState(context);
         if (savedNightModeState != -1 && savedNightModeState != currentNightModeState) {
             switch (savedNightModeState) {
                 case Configuration.UI_MODE_NIGHT_NO:
                     // turn off night mode
-                    deactivateNightMode(activity);
+                    deactivateNightMode(context);
                     break;
                 case Configuration.UI_MODE_NIGHT_YES:
                     // turn on night mode
-                    activateNightMode(activity);
+                    activateNightMode(context);
                     break;
                 case Configuration.UI_MODE_NIGHT_UNDEFINED:
                     // turn off night mode
-                    deactivateNightMode(activity);
+                    deactivateNightMode(context);
                     break;
             }
-            activity.recreate(); // todo check if necessary
         }
     }
 
@@ -87,12 +81,8 @@ public final class NightModeHelper implements TrackbookKeys {
 
 
     /* Activates Night Mode */
-    private static void activateNightMode(Activity activity) {
-        saveNightModeState(activity, Configuration.UI_MODE_NIGHT_YES);
-
-        // revert to normal status bar
-        View decorView = activity.getWindow().getDecorView();
-        decorView.setSystemUiVisibility(0);
+    private static void activateNightMode(Context context) {
+        saveNightModeState(context, Configuration.UI_MODE_NIGHT_YES);
 
         // switch to Nighh Mode
         AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_YES);
@@ -100,17 +90,9 @@ public final class NightModeHelper implements TrackbookKeys {
 
 
     /* Deactivates Night Mode */
-    private static void deactivateNightMode(Activity activity) {
+    private static void deactivateNightMode(Context context) {
         // save the new state
-        saveNightModeState(activity, Configuration.UI_MODE_NIGHT_NO);
-
-        // switch to white status bar - if possible
-        View decorView = activity.getWindow().getDecorView();
-        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
-            decorView.setSystemUiVisibility(View.SYSTEM_UI_FLAG_LIGHT_STATUS_BAR);
-        } else {
-            decorView.setSystemUiVisibility(0);
-        }
+        saveNightModeState(context, Configuration.UI_MODE_NIGHT_NO);
 
         // switch to Day Mode
         AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_NO);
@@ -132,4 +114,3 @@ public final class NightModeHelper implements TrackbookKeys {
     }
 
 }
-