public static void hideRightColumnInLandscapeMode(final AppCompatActivity activity) {
        final Fragment rightColumn = activity.getSupportFragmentManager().findFragmentById(R.id.settings_fragment_content_root);
        if (rightColumn != null) {
            activity.getSupportFragmentManager()
                    .beginTransaction()
                    .remove(rightColumn)
                    .commit();
            activity.findViewById(R.id.settings_fragment_divider).setVisibility(View.GONE);
            activity.findViewById(R.id.settings_fragment_content_root).setVisibility(View.GONE);
        }

    }
for theme settings, don't show second column in landscape mode
main/src/main/java/cgeo/geocaching/settings/SettingsActivity.java