Object-Oriented Programming (Narva College) 2019/20 spring

Chapter 8

Example program

In the previous examples, the mouse and the action events were demonstrated. In fact, there are many more options. In the following example, quite a few of events are demonstrated. Because the number of event classes is quite small, the "change listener" (an instance of the class that implements the ChangeListener interface) is used for the many graphical components. To implement the ChangeListener interface, the method changed must be specified. Various properties of different graphical components can be listened to - for example, changes of the window size (e.g. widthProperty and heightProperty of class Stage). In the following example, the selected list view property selectedItemProperty is listened to.

public void start(Stage primaryStage) {
    // create a border pane
    BorderPane borderpane = new BorderPane();

    // create a text field and add it to the top of the border pane
    TextField textfield = new TextField();
    textfield.setText("some text");
    borderpane.setTop(textfield);

    // create and register a handler for the key event
    // (reacts only on the ENTER key)
    textfield.setOnKeyPressed(new EventHandler<KeyEvent>() {
        public void handle(KeyEvent keyEvent) {
            if (keyEvent.getCode() == KeyCode.ENTER) {
                textfield.setText("I have pressed the ENTER key");
            }
        }
    });

    // create a list view and add it to the center of the border pane
    ListView<String> list = new ListView<String>();
    ObservableList<String> items = FXCollections.observableArrayList("First", "Second",
            "Third", "Fourth");
    list.setItems(items);
    borderpane.setCenter(list);

    // create and register listener for the property of the list view
    // (property changes if something is selected)
    list.getSelectionModel().selectedItemProperty().addListener(new ChangeListener<String>() {
        public void changed(ObservableValue<? extends String> ov, String oldValue, String newValue) {
            textfield.setText(newValue);
        }
    });


    // the second border pane is added to the bottom of the first border pane
    // two buttons are added to the left and right of the second border pane
    BorderPane borderpane2 = new BorderPane();
    Button button1 = new Button("1");
    borderpane2.setLeft(button1);
    Button button2 = new Button("2");
    borderpane2.setRight(button2);
    borderpane.setBottom(borderpane2);

    // create and register a handler for the mouse event on the second border pane
    borderpane2.setOnMouseClicked(new EventHandler<MouseEvent>() {
        public void handle(MouseEvent me) {
            textfield.setText("new text now");
        }
    });


    // create and register a handler for the key event on the first button
    button1.setOnKeyPressed(new EventHandler<KeyEvent>() {
        public void handle(KeyEvent keyEvent) {
            if (keyEvent.getCode() == KeyCode.DIGIT1) {
                textfield.setText("now 1");
            }
        }
    });


    // create and register a handler for the mouse event on the second button
    button2.setOnMouseClicked(new EventHandler<MouseEvent>() {
        public void handle(MouseEvent me) {
            textfield.setText("now 2");
        }
    });


    // create and register a handler for window event
    primaryStage.setOnHiding(new EventHandler<WindowEvent>() {
        public void handle(WindowEvent event) {
            // create the second stage
            Stage question = new Stage();
            // label with a question and two buttons
            Label label = new Label("Are you sure you want to close the window?");
            Button okButton = new Button("Yes");
            Button cancelButton = new Button("No");

            // create and register a handler for the Yes button
            okButton.setOnAction(new EventHandler<ActionEvent>() {
                public void handle(ActionEvent event) {
                    question.hide();
                }
            });

            // create and register a handler for the No button
            cancelButton.setOnAction(new EventHandler<ActionEvent>() {
                public void handle(ActionEvent event) {
                    primaryStage.show();
                    question.hide();
                }
            });

            // group the buttons
            FlowPane pane = new FlowPane(10, 10);
            pane.setAlignment(Pos.CENTER);
            pane.getChildren().addAll(okButton, cancelButton);

            // the question and the group of buttons are added to vertical box
            VBox vBox = new VBox(10);
            vBox.setAlignment(Pos.CENTER);
            vBox.getChildren().addAll(label, pane);

            // create a scene and display the stage
            Scene scene2 = new Scene(vBox);
            question.setScene(scene2);
            question.show();
        }
    }); //the end of the window event


    // create a scene and display the stage
    Scene scene = new Scene(borderpane, 300, 150, Color.SNOW);
    primaryStage.setTitle("Events");
    primaryStage.setResizable(false);
    primaryStage.setScene(scene);
    primaryStage.show();
}

Chapter 8