@FXML Annotation not working correctly

Question

I'm currently working on a 'small' project with JavaFX. I used the SceneBuilder to create the first sketch of my GUI. it still needs some adjustment and styling but I wanted to see if it's working so far.

I have 2 hyperlinks on the GUI, if the user clicks one of them the default system-browser should open with a specific URL.

So far I got this:

Main.java:

public class Main extends Application {

@Override
public void start(Stage primaryStage) throws MalformedURLException, IOException {

    DataBean dataBean= new DataBean(primaryStage);
    Controller controller = new Controller(dataBean);
    controller.show();
}

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

DataBean.java:

public class DataBean {

private Stage primaryStage;

public DataBean(Stage stage) {

    primaryStage = stage;
}

public Stage getPrimaryStage() {
    return primaryStage;
}
}

TestautomatView.java:

public class TestautomatView implements Initializable {

@FXML 
private ComboBox<String> environmentCombo;

@FXML 
private Hyperlink crhl;

@FXML
private Hyperlink help;

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

}

private Scene scene;
private BorderPane root;

public TestautomatView() throws MalformedURLException, IOException {
    root = FXMLLoader.load(new URL(TestautomatView.class.getResource("Sample.fxml").toExternalForm()));

    scene = new Scene(root);
}

public void show(Stage stage) {
    stage.setTitle("CrossReport Testautomat");
    stage.setScene(scene);
    stage.show();
}


public ComboBox<String> getEnvironmentCombo() {
    return environmentCombo;
}

public Hyperlink getCrhl() {
    return crhl;
}

public Hyperlink getHelp() {
    return help;
}

public Scene getScene() {
    return scene;
}

}

In my controller I want to set the ActionHandler to the hyperlinks but it's not working because the getters in my view return null.

public class Controller  {

private DataBean dataBean;
private TestautomatView view;

public Controller(DataBean databean) throws MalformedURLException, IOException {
    this.dataBean = databean;
    this.view = new TestautomatView();

    setActionHandlers();
}

public void show() throws MalformedURLException, IOException {
    view.show(dataBean.getPrimaryStage());
}

private void setActionHandlers() {
//      setHyperlink(view.getCrhl(), "www.example.com");
//      setHyperlink(view.getHelp(), "www.example2.com");
}

private void setHyperlink(Hyperlink hl, String uri) {
    hl.setOnAction(new EventHandler<ActionEvent>() {
        @Override
        public void handle(ActionEvent event) {
            //TODO - Open Default Browser
        }
    });
}

}

When I start my application, I can see the GUI but when I want to add the ActionHandlers I get a NullPointerException.

In the ´Sample.fxml´ file the hyperlinks are children of a HBox

<Hyperlink fx:id="crhl" text="Report" />
<Hyperlink fx:id="help" text="Help" />

But it's not just the hyperlinks even the ComboBox is null when I inspect my app in the debugger.

Where is my mistake?

Answer 1

As pointed out in another answer, the issue is that you create an instance of TestautomatView "by hand". The default behavior of the FXMLLoader is to create an instance of the controller class specified in the FXML file, and use that instance as the controller. Consequently, you have two instances of TestautomatView: the one you created (and have a reference to), and the one that was created by the FXMLLoader. It is the second one that has the @FXML-annotated fields initialized.

You can change this default behavior by creating an FXMLLoader instance, and setting the controller on it directly. E.g. consider doing:

public class TestautomatView implements Initializable {

    @FXML 
    private ComboBox<String> environmentCombo;

    @FXML 
    private Hyperlink crhl;

    @FXML
    private Hyperlink help;

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

    }

    private Scene scene;
    private BorderPane root;

    public TestautomatView() throws MalformedURLException, IOException {

        FXMLLoader loader = new FXMLLoader(TestautomatView.class.getResource("Sample.fxml"));
        loader.setController(this);
        root = loader.load();

        scene = new Scene(root);
    }

    // etc...

}

Since you are directly setting the controller, you need to remove the fx:controller attribute from the Sample.fxml file for this to work.

You may also be interested in this pattern, which is quite similar (though not exactly the same) as what you are trying to do here.