CODEWITHSUNDEEP
javajavafxeventhandler
user3870075
user3870075

Reputation: 141

JavaFx: Access an object from Event handler

I want to make a program in JavaFX that contains a button which, when clicked, a circle gets created and added to an ArrayList of shapes. The following is my code:

createCircleBtn.setOnMouseClicked(new EventHandler<MouseEvent>() {
    @Override
        public void handle(MouseEvent event) {
            Circle circle1 = new Circle();
            shapes.add(circle1);
            circle1.setCenterX(event.getX());
            circle1.setCenterY(event.getY());
            circle1.setOnMouseDragged(new EventHandler<MouseEvent>() {
                @Override
                public void handle(MouseEvent event) {
         // doesn't work because "circle1" must be declared final (constant) 
                    circle1.setCenterX(event.getX());
                    // "this" doesn't refer to "circle1"
                    this.setCenterY(event.getY());
                }
            });
            mainPane.getChildren().add(circle1);
        }
    });

My question is - How can I access "circle1" from inside handle method? In JavaScript we use e.currentTarget.

I'm unable to declare "circle1" final because I will need to change it afterwards.

Upvotes: 1

Views: 3958

Answers (2)

Uluk Biy
Uluk Biy

Reputation: 49215

Use event.getSource(), by this can write a common event handler for multiple cicrles without worrying which exact one was clicked:

EventHandler<MouseEvent> handler = new EventHandler<>()
{
    @Override
    public void handle( MouseEvent event )
    {
        if (event.getSource() instanceof Circle) { // to be on safe side, you may 
                                                   // remove this if-statement 
                                                   // if you are sure
            Circle c = (Circle) event.getSource();
            c.setCenterX( event.getX() );
        }
    }
};

// use it on multiple circles
circle1.setOnMouseDragged(handler);
circle2.setOnMouseDragged(handler);
...
circleN.setOnMouseDragged(handler);

Upvotes: 0

James_D
James_D

Reputation: 209714

Nowhere in the code you show do you reassign circle1, so you can just declare it as final:

createCircleBtn.setOnMouseClicked(new EventHandler<MouseEvent>() {
    @Override
        public void handle(MouseEvent event) {
            final Circle circle1 = new Circle();
            shapes.add(circle1);
            circle1.setCenterX(event.getX());
            circle1.setCenterY(event.getY());
            circle1.setOnMouseDragged(new EventHandler<MouseEvent>() {
                @Override
                public void handle(MouseEvent event) {
                    circle1.setCenterX(event.getX());
                }
            });
            mainPane.getChildren().add(circle1);
        }
    });

Note that in Java 8 your code would compile just as you have it, because circle1 is effectively final (meaning that it is only assigned once and is never reassigned).

Upvotes: 2

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