Theming: enable day/night mode incl. app-wide setting.

src/main/java/de/dennisguse/opentracks/util/ActivityUtils.java

@@ -16,6 +16,7 @@ import android.widget.AbsListView;
 import android.widget.ListView;
 import android.widget.Toast;
 
+import androidx.appcompat.app.AppCompatDelegate;
 import androidx.appcompat.widget.SearchView;
 
 import java.util.ArrayList;
@@ -151,4 +152,7 @@ public class ActivityUtils {
         toast.show();
     }
 
+    public static void applyNightMode(Context context) {
+        AppCompatDelegate.setDefaultNightMode(PreferencesUtils.getDefaultNightMode(context));
+    }
 }

src/main/java/de/dennisguse/opentracks/util/PreferencesUtils.java

@@ -108,6 +108,8 @@ public class PreferencesUtils {
      * @param keyId   the key id
      * @param value   the value
      */
+    //TODO Don't use; this function is only to be used TrackRecordingService and will be removed.
+    @VisibleForTesting
     public static void setBoolean(Context context, int keyId, boolean value) {
         SharedPreferences sharedPreferences = getSharedPreferences(context);
         Editor editor = sharedPreferences.edit();
@@ -162,6 +164,8 @@ public class PreferencesUtils {
      * @param keyId   the key id
      * @param value   the value
      */
+    //TODO Don't use; this function is only to be used TrackRecordingService and will be removed.
+    @Deprecated
     @VisibleForTesting
     public static void setLong(Context context, int keyId, long value) {
         SharedPreferences sharedPreferences = getSharedPreferences(context);
@@ -189,6 +193,7 @@ public class PreferencesUtils {
      * @param keyId   the key id
      * @param value   the value
      */
+    @VisibleForTesting
     public static void setString(Context context, int keyId, String value) {
         SharedPreferences sharedPreferences = getSharedPreferences(context);
         Editor editor = sharedPreferences.edit();
@@ -347,6 +352,16 @@ public class PreferencesUtils {
         return getBoolean(context, R.string.import_prevent_reimport_key, defaultValue);
     }
 
+    /**
+     * @return {@link androidx.appcompat.app.AppCompatDelegate}.MODE_*
+     */
+    public static int getDefaultNightMode(Context context) {
+        final String defaultValue = getKey(context, R.string.night_mode_default);
+        final String value = getString(context, R.string.night_mode_key, defaultValue);
+
+        return Integer.parseInt(value);
+    }
+
     @Deprecated //Use TrackRecordingService
     public static boolean isRecording(Context context) {
         return isRecording(getRecordingTrackId(context));