Realm Singleton instance for UI thread from Book Example

realm-ui-thread-singleton.java

public class BooksScopeListener extends Fragment { // could go to base class
    public BooksScopeListener() {
        setRetainInstance(true);
        RealmManager.incrementCount();
    }

    @Override
    public void onDestroy() {
        RealmManager.decrementCount();
        super.onDestroy();
    }
}

public class BooksActivity extends AppCompatActivity {
    Realm realm;
  
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        RealmManager.initializeRealmConfig(getApplicationContext()); // could go to base class
        super.onCreate(savedInstanceState);
        BooksScopeListener fragment = (BooksScopeListener) getSupportFragmentManager().findFragmentByTag("SCOPE_LISTENER"); // could go to base class
        if(fragment == null) {
            fragment = new BooksScopeListener();
            getSupportFragmentManager().beginTransaction().add(fragment, "SCOPE_LISTENER").commit();
        }
        //get realm instance
        realm = RealmManager.getRealm();