Store dynamic screen with multiple stages

Question

I´ve got 2 different screens, in the first screen the user can load images and the other one is just a single button (the stage is invisible so the stage has to be different

Answer 1

You have to store a reference to your stage content, so you don't have to reinstantiate it. One possibility is to store it in the mainController and provide an EventHandler to your subController, to switch the stage

public interface ScreenController {
        void setOnSwitchStage(EventHandler handler);
}

public class Screen1Controller implements Initializable, ScreenController {

    @FXML
    private Button btnSwitchScreen

    public Screen1Controller() {
    }

    @Override
    public void initialize(URL location, ResourceBundle resources) {
    }

     @Override
    public void setOnSwitchStage(EventHandler handler) {
        btnSwitchScreen.setOnAction(handler);
    }
}

public class YourApp extends Application {

    @Override
    public void start(Stage primaryStage) throws Exception {
        Stage secondaryStage = new Stage();

        initScreen(primaryStage, secondaryStage, "screen1.fxml");
        initScreen(secondaryStage, primaryStage, "screen2.fxml");

        primaryStage.show();
    }

    private void initScreen(Stage parentStage, Stage nextStage, String resource) throws IOException {
    FXMLLoader loader = new FXMLLoader(getClass().getResource(resource));
    Scene scene = new Scene(loader.load());
    parentStage.setScene(scene);

    ScreenController screenController = loader.getController();
    screenController.setOnSwitchStage(evt -> {
        nextStage.show();
        parentStage.hide();
    });
}

    public static void main(String[] args) {
        launch(args);
    }
}