How to change button label while loading content

Question

I have this basic example with toggle buttons:
public class test extends Application
    @Override
    public void start(Stage primaryStage)
        final VBox vbox = new VBox();
        String pillButtonCss = DX57DC.class.getResource("PillButton.css").toExternalForm();
        // create 3 toggle buttons and a toogle group for them
        ToggleButton tb1 = new ToggleButton("Left Button");
        tb1.setId("pill-left");
        ToggleButton tb2 = new ToggleButton("Center Button");
        tb2.setId("pill-center");
        ToggleButton tb3 = new ToggleButton("Right Button");
        tb3.setId("pill-right");
        final ToggleGroup group = new ToggleGroup();
        tb1.setToggleGroup(group);
        tb2.setToggleGroup(group);
        tb3.setToggleGroup(group);
        // select the first button to start with
        group.selectToggle(tb1);
        final Rectangle rect1 = new Rectangle(300, 300);
        rect1.setFill(Color.DARKOLIVEGREEN);
        final Rectangle rect2 = new Rectangle(300, 300);
        rect2.setFill(Color.LAVENDER);
        final Rectangle rect3 = new Rectangle(300, 300);
        rect3.setFill(Color.LIGHTSLATEGREY);
        tb1.setUserData(rect1);
        tb2.setUserData(rect2);
        tb3.setUserData(rect3);
        group.selectedToggleProperty().addListener(new ChangeListener<Toggle>()
            @Override
            public void changed(ObservableValue<? extends Toggle> ov, Toggle toggle, Toggle new_toggle)
                if (new_toggle == null)
                else
                    vbox.getChildren().set(1, (Node) group.getSelectedToggle().getUserData());
        HBox hBox = new HBox();
        hBox.getChildren().addAll(tb1, tb2, tb3);
        hBox.setPadding(new Insets(10, 10, 10, 10));
        hBox.getStylesheets().add(pillButtonCss);
        vbox.getChildren().addAll(hBox, (Node) group.getSelectedToggle().getUserData());
        StackPane root = new StackPane();
        root.getChildren().add(vbox);
        Scene scene = new Scene(root, 800, 850);
        primaryStage.setScene(scene);
        primaryStage.show();
    public static void main(String[] args)
        launch(args);
I noticed that if I put heavy business logic into the buttons while I switch the buttons it appears that the application hangs.
Is it possible to display "Loading.." instead of the button label while I switch the buttons?

Answer 1

Welcome to the world of multithreaded programming in JavaFX...
It's generally a mistake to perform any long-running task in the FX Application thread, as it will cause the UI to hang while it's running. You should use the javafx.concurrent package to perform background tasks; the Task class in particular will be useful to you. The javadocs have plenty of examples.
Note that it's also a mistake to modify the UI from a background thread, and that your Task implementation's call(...) method will be executed on a background thread. The Task class provides setOnSucceeded, setOnFailed, setOnCancelled methods to register a handler whose handle(...) method will be executed back on the FX Application thread.
For example, the basic strategy to respond to a button press by updating the UI, launching a long-running process, and then updating the UI with the results of that process is as follows. Replace 'T' with any data type.
myButton.setOnAction(new EventHandler<ActionEvent>() {
     @Override
     public void handle(ActionEvent event) {
          final Task<T> longRunningTask = new Task<T>() {
               @Override
               public T call() {
                    // perform long running operation:
                    T result = computeResult();    
                    return result ;    
          longRunningTask.setOnSucceeded(new EventHandler<WorkerStateEvent>() {
               @Override   
               public void handle(WorkerStateEvent event) {
                    // get result of long running operation:    
                    T result = longRunningTask.getValue();
                    // now update UI on basis of result to indicate task is complete
          // update UI here to indicate task is about to run...
          // now start task:
          Thread t = new Thread(longRunningTask);
          t.setDaemon(true);
          t.start();
There's a bunch of other functionality in Task, such as a progress property and a message property. These can be bound, and updated on the FX Application thread via the appropriate updateXXX(...) methods.