Multiple FXML with Controllers, share object

Question

Goodevening everyone,

I have found a bunch of posts already on this topic but I still can not manage to pass an object from Controller1 to Controller2. Is there somewhere a full tutorial or some example project that does this?

I've gotten this far until I got stuck:

Country class

public class Country {
private SimpleStringProperty country = new SimpleStringProperty("");

//Constructor
public Country() {
}

//GETTERS
public String getCountry() {
    return country.get();
}

//SETTERS
public void setCountry(String value) {
    country.set(value);
}

@Override
public String toString() {
    return getCountry();
}
}

When the program starts, the main FXML gets loaded (Sample.fxml). This contains a border pane with a menu bar in the top panel and a content pane in the center. On initialize I create a new Country object and store it in a global variable. I have a method that loads another FXML into the content pane when a menu item is clicked:

SampleController.java

public class SampleController implements Initializable {

@FXML
private Pane pContent;

private Country c;

@FXML
private void handleButtonAction(ActionEvent event) throws IOException {
    System.out.println(c); //this prints Belgium, which is correct

    URL url = getClass().getResource("Sub1.fxml");

    FXMLLoader fxmlloader = new FXMLLoader();
    fxmlloader.setLocation(url);
    fxmlloader.setBuilderFactory(new JavaFXBuilderFactory());

    pContent.getChildren().clear();
    pContent.getChildren().add((Node) fxmlloader.load(url.openStream()));
}

@Override
public void initialize(URL url, ResourceBundle rb) {
    c = new Country();
    c.setCountry("Belgium");
}

public Country getCountryFromSampleController(){
    return c;
}
}

Now I wish to capture the Country object when the Sub1.fxml gets loaded, which means I need to fetch the country object on initialize():

Sub1Controller.java

public class Sub1Controller implements Initializable {

/**
 * Initializes the controller class.
 */
@Override
public void initialize(URL url, ResourceBundle rb) {
    SampleController sp = new SampleController(); //I don't know how to fetch the original SampleController object
    System.out.println(sp.getCountryFromSampleController()); 
    //this prints null, which is ofcourse logical because I make a new SampleController object.         
}    
}

The question that I have, how can I get the 'original' SampleController object so I can use the getCountryFromRoot() method to fetch the Country object with value Belgium? I've been searching on this issue for hours and hours and have read every post on StackOverflow about this, but it seems I do not find the missing link... any help (preferably with this code) is appreciated!

Sorry for the long post, I tried to be as complete as possible else I'll never understand...

Answer 1

FXML is a simple form of MVC pattern. FXML file is a view, Controller is obvious, what's missed? The model -- a place where you store all data relative to your current view and, thus, which you can use to share Country data between controllers.

---

1. One of the possible approach to introduce model is "context". Let's consider a case, then you have only one model for the whole project so you can have a global context in a form of Singleton

public class Context {
    private final static Context instance = new Context();

    public static Context getInstance() {
        return instance;
    }

    private Country country = new Country();

    public Country currentCountry() {
        return country;
    }
}

Your SampleController will have next changes:

@Override
public void initialize(URL url, ResourceBundle rb) {
    Context.getInstance().currentCountry().setCountry("Belgium");
}

And SubController1 can access it the same way:

@Override
public void initialize(URL url, ResourceBundle rb) {
    System.out.println(Context.getInstance().currentCountry().getCountry());
}

---

2. Another way is to pass context to SubController1 then you load it's xml. It will work better if you don't want to have application global model. So create similar Context class but without instance fields, and:

public class Sub1Controller implements Initializable {
    private Context context;
    public void setContext(Context context) {
        this.context = context;
        // initialize country dependent data here rather then in initialize()
    }
}

Setting context in SampleController:

Context currentContext = new Context();

@Override
public void initialize(URL url, ResourceBundle rb) {
    currentContext.currentCountry().setCountry("Belgium");
}

@FXML
private void handleButtonAction(ActionEvent event) throws IOException {
    URL url = getClass().getResource("Sub1.fxml");

    FXMLLoader fxmlloader = new FXMLLoader();
    fxmlloader.setLocation(url);
    fxmlloader.setBuilderFactory(new JavaFXBuilderFactory());

    pContent.getChildren().clear();
    pContent.getChildren().add((Node) fxmlloader.load(url.openStream()));
            // here we go
    ((Sub1Controller)fxmlloader.getController()).setContext(currentContext);
}