Switching to different screens JavaFX and FXML

Question

I'm new to JavaFX and while doing my project I'm trying to switch screens. I'm thinking of setting of corresponding AnchorPane visibility true or false and I'm having problem when accessing to AnchorPane from another Controller. I tried to make AnchorPane static but it gives NullPointerException.

This is my code.

Controller class

public class Controller {

    @FXML
    AnchorPane signInPane;

    @FXML
    private TextField usernameForSignIn;

    @FXML
    private PasswordField password;

    @FXML
    private Button signIn;

    @FXML
    private Button registration;

    @FXML
    void initialize() {
        registration.setOnAction(event -> {
            signInPane.setVisible(false);
            SignUpController.registerPane.setVisible(true);
        });

        signIn.setOnAction(event ->  {
            String usernameText = usernameForSignIn.getText().trim();
            String passwordText = password.getText().trim();

            if(!usernameText.equals("") && !passwordText.equals("")) {
                loginUser(usernameText, passwordText);
            } else {
                System.out.println("Empty login and/or password");
            }

        });
    }

    private void loginUser(String usernameText, String passwordText) {
    }

}

SignUpController Class

public class SignUpController {

    @FXML
    static AnchorPane registerPane;

    @FXML
    private TextField email;

    @FXML
    private PasswordField pass;

    @FXML
    private Button signUp;

    @FXML
    private TextField fname;

    @FXML
    private TextField lname;

    @FXML
    private TextField username;

    @FXML
    private RadioButton radioMale;

    @FXML
    void initialize() {

        signUp.setOnAction(event -> {

            signUpNewUser();

        });
    }

    private void signUpNewUser() {
        DatabaseHandler databaseHandler = new DatabaseHandler();

        String firstName = fname.getText();
        String lastName = lname.getText();
        String usname = username.getText();
        String password = pass.getText();
        String e_mail =  email.getText();
        String gender = "";
        if(radioMale.isSelected()) {
            gender = "Male";
        } else {
            gender = "Female";
        }

        User user = new User(firstName,lastName,usname,password,e_mail,gender);

        databaseHandler.signUpUser(user);

    }
}

I need to go from this screen

to this without closing the window

I tried to solve the problem like this, but it closes the window and opens a new one.

registration.setOnAction(event -> {
    registration.getScene().getWindow().hide();

    FXMLLoader loader = new FXMLLoader();
    loader.setLocation(getClass().getResource("/sample/view/signUp.fxml"));

    try {
        loader.load();
    } catch (IOException e) {
        e.printStackTrace();
    }

    Parent root = loader.getRoot();
    Stage stage = new Stage();
    stage.setScene(new Scene(root));
    stage.showAndWait();

// signInPane.setVisible(false);
});

Answer 1

Create a single window and reuse it, instead of creating a new one each time. Then you can either just check if it is showing, or you can disable whichever control shows it when it is showing.

Answer 2

Something like this will ensure that your FXML is loaded before the initalize(). You do not have to hide your AnchorPane, as the instances are already loaded. Hiding items created from FXML usually causes errors.

public class Controller {

    @FXML
    Button button_CustomerInfo;
    @FXML
    Button button_A1Child;
    @FXML
    BorderPane bPane;
    @FXML
    ToggleGroup tog;
    Parent r1;
    Parent r2;

    // CREATE SOMETHING LIKE THIS
    // THIS SAMPLE CODE USES THE SAME BORDERPANE
    // AND THE CENTER OF THE BORDERPANE
    // IS CHANGED WHEN A BUTTON IS PRESSED
    {
        try {
            r1 = FXMLLoader.load(getClass().getResource("SecondSreen.fxml"));
            r2 = FXMLLoader.load(getClass().getResource("FirstScreen.fxml"));
        } catch (IOException e) {
            e.printStackTrace();
        }


    }

    public void initialize() {


        button_CustomerInfo.setOnAction(e-> {
            bPane.setCenter(r2);
        });

        button_A1Child.setOnAction(e-> {
            bPane.setCenter(r1);
        });
    }
}