Using showAndWait in the onFinished EventHandler of an Animation doesn't work

Question

In JavaFx, I want to show a modal dialog after an animation ends. For some reason, calling showAndWait in the EventHandler that gets executed after the animation ends doesn't work. A new window is shown, but it seems like nothing is drawn inside it.

This example demonstrates the issue:

public void start(Stage primaryStage) {
    Rectangle rect = RectangleBuilder.create().width(200).height(200).fill(Color.RED).build();

    StackPane root = new StackPane();
    root.getChildren().add(rect);

    Timeline animation = new Timeline();
    animation.getKeyFrames().addAll(
            new KeyFrame(new Duration(1000),
                         new KeyValue(rect.widthProperty(), 100),
                         new KeyValue(rect.heightProperty(), 100)),
            new KeyFrame(new Duration(2000),
                         new KeyValue(rect.widthProperty(), 300),
                         new KeyValue(rect.heightProperty(), 300))
    );
    animation.setOnFinished(new EventHandler<ActionEvent>() {

        @Override
        public void handle(ActionEvent t) {
            Stage stage = new Stage();
            StackPane pane = new StackPane();
            pane.getChildren().add(new Label("Hello world"));
            stage.setScene(new Scene(pane, 100, 100));
            stage.showAndWait();
        }
    });
    animation.setCycleCount(1);

    Scene scene = new Scene(root, 300, 300);
    primaryStage.setScene(scene);
    primaryStage.show();

    animation.play();
}

The full code can be found at https://gist.github.com/bmesuere/9605866

I'd like to know why this doesn't work (on my macbook using java 1.7.0_51) and get suggestions for a workaround.

Answer 1

It seems to work if you wrap the code to show the stage in a Platform.runLater():

animation.setOnFinished(new EventHandler<ActionEvent>() {

            @Override
            public void handle(ActionEvent t) {
                Platform.runLater(new Runnable() {
                    @Override
                    public void run() {
                        Stage stage = new Stage();
                        StackPane pane = new StackPane();
                        pane.getChildren().add(new Label("Hello world"));
                        stage.setScene(new Scene(pane, 100, 100));
                        stage.showAndWait();                        
                    }
                });

            }
        });

No idea why. It fails on Java FX 8 too.