JavaFX: data transfer between controllers is always zero

I want to apologize in advance as this is discussed earlier in Passing Parameters Directly from Caller to Controller , but I've followed every possible solution I found and yet I can't get it to work.

I find it difficult to pass a parameter from one controller to another.

In particular:

LoginController passes username

to MainController .

When the login button is clicked, the LoginController sets username

to the MainController . But Main.fxml username

is NULL when loaded .

As I try to figure it out, I would like to ask:

• When is the MainController method calledinitialize()
  
  ? I suppose by the time the LoginController calls st.show();
  
  ?
• If the previous is correct, then why is the MainController username
  
  NULL since we have already set its value in the LoginController using mainController.setUsername(username)
  
  ?

Any help would be appreciated.

This is my code.

LoginController.java

public class LoginController implements Initializable {
    ...
    @FXML TextField username;

    @FXML public void actionLoginButton() {
        ...
        Stage st = new Stage();
        FXMLLoader loader = new FXMLLoader(getClass().getResource("Main.fxml"));
        Region root = (Region) loader.load();

        Scene scene = new Scene(root);
        st.setScene(scene);

        MainController mainController = loader.<MainController>getController();
        mainController.setUsername(username.getText());

        st.show();
    }
    ...
}

      

        
        
        
      

    

MainController.java

public class MainController implements Initializable {
    ...
    String username;

    @FXML Label lblWelcomeUser;

    public void setUsername(String usrname) {
        this.username = usrname;
    }

    @Override
    public void initialize(URL url, ResourceBundle rb) {
        ...    
        lblWelcomeUser.setText("Welcome, " + this.username);
        ...
    }
    ...
}