API за свързване

1. JavaFX Properties

For implementing the reactive model, JavaFX uses Properties – observable data containers. They store a value and notify registered observers whenever a change occurs.

Commonly used types:

• StringProperty
• IntegerProperty
• BooleanProperty

Properties are key to the automatic updating of the user interface.

2. Observer Pattern & ChangeListener

Since properties can change dynamically, JavaFX uses the Observer design pattern, in which:

• The Property is the observed object;
• The ChangeListener is the observer.
• addListener() The method is used to register a listener to a given Property and allows reacting to every change.
• Listeners can be::
  • ChangeListener
  • InvalidationListener

Example:

usernameField.textProperty().addListener(new ChangeListener<String>() {
    @Override
    public void changed(ObservableValue<? extends String> obs, String oldVal, String newVal) {
        validUsername.set(newVal.length() >= 4);
    }
});

Where obs is the object whose value has changed, oldVal is the value before the change, and newVal is the value after the change.

Since the event handling interface has only one method, we can treat it as a functional interface and replace these lines with a single lambda expression to make the code easier to read:

usernameField.textProperty().addListener(
    (obs, oldVal, newVal) ->
        validUsername.set(newVal.length() >= 4)
);

• JavaFX Binding

  Binding automates the observer mechanism and removes the need for manual listener management. It is implemented using the method bind

Example:

BooleanBinding formInvalid =
        validUsername.not().or(validPassword.not());

registerButton.disableProperty().bind(formInvalid);

In this case, the button is automatically disabled when a field is empty.

3. JavaFX Event Handling

While Property reacts to changes in state, Event Handling processes user actions.

The EventHandler interface defines the behavior for handling an event. In this interface, T is the type of event that the handler will receive. T must be a class that extends Event.

T	When it is used
ActionEvent	for buttons, menus
MouseEvent	for mouse actions
KeyEvent	for key presses
ScrollEvent	for scrolling
DragEvent	for drag & drop
TouchEvent	for touch events

button.setOnAction(new EventHandler<ActionEvent>() {
    @Override
    public void handle(ActionEvent event) {
        System.out.println("The button is pressed.");
    }
});

Since the event handling interface has only one method, we can treat it as a functional interface and replace these lines with a single lambda expression to make the code easier to read:

button.setOnAction(e -> {
    System.out.println("The button was pressed.");
});

4. JavaFX addEventHandler

addEventHandler() It provides extended control and allows adding multiple handlers for a single event.

Example:

button.addEventHandler(ActionEvent.ACTION, new EventHandler<ActionEvent>() {
    @Override
    public void handle(ActionEvent e) {
        System.out.println("Action handled");
    }
});

button.addEventHandler(ActionEvent.ACTION, e -> {
    System.out.println("Action handled");
});

The types of events are:

Event class	EventType
ActionEvent	ACTION
MouseEvent	MOUSE_CLICKED, MOUSE_PRESSED
KeyEvent	KEY_PRESSED, KEY_RELEASED, KEY_TYPED
ScrollEvent	SCROLL, SCROLL_STARTED