[FIXED] Pass object from main class to JavaFX Application

Issue

I have simple main class. There i try pass user to WindowLogin :

package client;


public class Client{

    public User user;

    public static void main(String[] args) {

        try {
            Client client = new Client();
            client.run(args);
        } catch (Exception e) {
            System.out.println("[ERR] Fatal error");
        }

    }

    public void run(String[] args)
    {

        user = new User();

        WindowLogin windowLogin = new WindowLogin();
        windowLogin.user = user;
        windowLogin.show();

    }

}

Window main class. There i try call test() function of user (in real, i need it pass to WindowMainController):

package client;

import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Scene;
import javafx.stage.Stage;
import javafx.scene.Parent;

import java.io.IOException;

public class WindowLogin extends Application{

    private Stage stage;
    public User user;

    @Override
    public void start(Stage primaryStage) throws Exception {
        stage = new Stage();
        try {
            FXMLLoader fxmlLoader = new FXMLLoader(getClass().getResource("views/WindowLogin.fxml"));

            WindowLoginController controller =
                    fxmlLoader.<WindowLoginController>getController();

            user.test();

            Parent root = fxmlLoader.load();
            Scene scene = new Scene(root);
            stage.setScene(scene);
            stage.show();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public void show(){
        launch();
    }
    public void hide() { stage.hide(); }

}

When i try to run it all:

Exception in Application start method

Of course (maybe :) ) it because of user in windowLogin is null.

What i doing wrong? How pass user to windowLogin? (i wont use Singletone)

---

Update:

I need use user in start() method, as i said before - i need pass user to WindowMainController

Solution

OverView

The problem you are facing here is on calling launch(), Javafx thread creates a new object of WindowLogin. So the object that you have created for WindowLogin and assigned user to it is no longer used in the start method !

 WindowLogin windowLogin = new WindowLogin();
 windowLogin.user = user;

You can overcome this by declaring the User in WindowLogin as static !

public static User user;

This will help to just keep on instance of the User

Answered By - ItachiUchiha