Basic JavaFX projects (Part 2)

JavaFX Mouse Event Example

Here is an example of capturing mouse events in JavaFX. 

Clone this repository into Eclipse as was specified in a previous post. (Git Repository view, clone a Git Repository).  The URI is https://github.com/cajanssen/JavaFXMouseEvent.git

After the project is created, as before (previous post) do some JavaFX project specific configuration in Eclipse.  (Add the already created user library and modify the Run configuration.)

Javadocs for JavaFX classes: https://openjfx.io/javadoc/13/allclasses-index.html

Code:

package jansproj.basicfx;

import javafx.application.Application;
import javafx.event.EventHandler;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.scene.input.MouseEvent;
import javafx.scene.paint.Color;
import javafx.stage.Stage;

public class MouseEventExample extends Application
{
    public MouseEventExample()
    {
    }

    // this application waits for and reacts to mouse click events
   
    @Override
    public void start(Stage stage) throws Exception
    {
        // Stage, Scene, root Node - standard stuff common to JavaFX programs
        stage.setTitle("Mouse Event Example");
        Group root = new Group();
        Scene scene = new Scene(root);
        stage.setScene(scene);

        int canvasWidth = 1000;
        int canvasHeight = 500;
        int canvasXCenter = canvasWidth / 2;
        int canvasYCenter = canvasHeight / 2;

        Canvas canvas = new Canvas(canvasWidth, canvasHeight);
       
        // rather than create a large tree of nodes, create a tree of only
        // one node - canvas - and draw on that
        root.getChildren().add(canvas);
       
        double blackCircleRadius = 250;
        double blueCircleRadius = 200;
        double redCircleRadius = 150;
        double goldCircleRadius = 100;

        // make concentric circles
        // drawing point for strokeOval() is the upper left corner of bounding box, not the center
        GraphicsContext gc = canvas.getGraphicsContext2D();
        gc.setLineWidth(4.0);
        gc.setStroke(Color.BLACK);
        gc.strokeOval((canvasXCenter - blackCircleRadius), (canvasYCenter - blackCircleRadius), blackCircleRadius*2, blackCircleRadius*2);
         gc.setStroke(Color.BLUE);
        gc.strokeOval((canvasXCenter - blueCircleRadius), (canvasYCenter - blueCircleRadius), blueCircleRadius*2, blueCircleRadius*2);
        gc.setStroke(Color.RED);
        gc.strokeOval((canvasXCenter - redCircleRadius), (canvasYCenter - redCircleRadius), redCircleRadius*2, redCircleRadius*2);
        gc.setStroke(Color.GOLD);
        gc.strokeOval((canvasXCenter - goldCircleRadius), (canvasYCenter - goldCircleRadius), goldCircleRadius*2, goldCircleRadius*2);

       
        // attach a Mouse Click event handler to the scene
        // rather than create the object elsewhere and pass it in to the setOnMouseClicked()
        // method, define the event handler right here with
        // an anonymous inner class - common practice
        scene.setOnMouseClicked(
            new EventHandler<MouseEvent>()
            {
                public void handle(MouseEvent e)
                {
                    System.out.println("x= " + e.getX() + " y= " + e.getY());
                    double distance = Math.sqrt(((canvasXCenter - e.getX()) * (canvasXCenter - e.getX())) + (canvasYCenter - e.getY()) *(canvasYCenter - e.getY()));
                    String location = "outside";
                    if ( distance < blackCircleRadius )
                        location = "black circle";
                    if ( distance < blueCircleRadius )
                        location = "blue circle";
                    if ( distance < redCircleRadius )
                        location = "red circle";
                    if ( distance < goldCircleRadius )
                        location = "gold circle";
                    System.out.println(location);
                }
            });

        // calling show() on the Stage is a standard requirement for a JavaFX program
        stage.show();
    }

    public static void main(String[] args)
    {
        launch(args);
    }
}

The tree of Nodes to be displayed is different than the previous example.  Instead of nesting multiple Node type objects within each other (FlowPane, Label, Button), there is only one Node object in the tree - Canvas - and all the drawing is done on that Node using GraphicsContext drawing method calls.

The application draws some concentric circles on the Canvas at known distances from the center.  These distances are then used by the MouseEvent EventHandler to determine where in the collection of circles the mouse click occurred.