鼠标包含在对象内

Question

I'm new to learning Java and for a few days I have searched for a way to click drawn objects, to contain the mouse within a object such as g.drawRect(x, x, x, x)...

I came across the code below, I'm trying to make it work so I can learn what is needed to contain the mouse within a object but I cant seem to make it work.

Got code from " Is there any way to add a MouseListener to a Graphic object? "

I've tried to make it work according to the tips they gave but no hope :(.

Any help is appreciated.

 import java.awt.*; import java.awt.event.MouseEvent; import java.awt.event.MouseListener; import java.awt.geom.Ellipse2D; import javax.swing.*; public class Gui3 extends JFrame { JFrame frame = new JFrame(); MyDrawPanel drawpanel = new MyDrawPanel(); public static void main(String[] args) { Gui3 gui = new Gui3(); gui.go(); } public void go() { frame.getContentPane().add(drawpanel); // frame.addMouseListener(this); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setSize(300, 300); frame.setVisible(true); } } class MyDrawPanel extends JComponent implements MouseListener { Ellipse2D oval = new Ellipse2D.Double(70, 70, 100, 100); public void paintComponent(Graphics g) { Graphics2D g2d = (Graphics2D) g; g2d.fillOval(70, 70, 100, 100); } @ Override public void mouseClicked(MouseEvent e) { if ((e.getButton() == 1) && oval.contains(e.getX(), e.getY())) { repaint(); JOptionPane.showMessageDialog(null, e.getX() + "\\n" + e.getY()); } } @ Override public void mouseEntered(MouseEvent e) { // TODO Auto-generated method stub } @ Override public void mouseExited(MouseEvent e) { // TODO Auto-generated method stub } @ Override public void mousePressed(MouseEvent e) { } @ Override public void mouseReleased(MouseEvent e) { // TODO Auto-generated method stub } public boolean contains(int x, int y) { return oval.contains(x, y); } } 

Answer 1

Your commented line hints at your issue - you never actually add a MouseListener to the GUI, so no one is being notified of mouse events. It appears you've made your panel the mouse listener (which is fine), so register it in a constructor for the MyDrawPanel class. Add this constructor to your MyDrawPanel, and you should be good to go.

public MyDrawPanel(){
    addMouseListener(this);
}

Also, it would probably be a good idea to draw your actual oval variable instead of using the drawOval(..) method of Graphics, because you are creating a shape in memory and an image that are disjoint from one another. Try this instead for your paintComponent(Graphics g) :

public void paintComponent(Graphics g) {
    Graphics2D g2d = (Graphics2D) g;
    g2d.fill(oval);
}

Answer 2

Basically, you need to register the MouseListener with the DrawPanel , you want to do this, because you want the mouse events to be within the context of the DrawPanel otherwise the MouseEvent location information won't be correct.

class MyDrawPanel extends JComponent implements MouseListener {

    Ellipse2D oval = new Ellipse2D.Double(70, 70, 100, 100);

    public MyDrawPanel() {
        addMouseListener(this);
    }

You will also want to call super.paintComponent before you do any custom painting

@Override
protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    Graphics2D g2d = (Graphics2D) g;

    g2d.fillOval(70, 70, 100, 100);

}

You should also ensure that you are creating/modifying your UI from within the context of the Event Dispatching Thread. See Initial Threads for more details

public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        @Override
        public void run() {
            try {
                UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
            } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                ex.printStackTrace();
            }

            Gui3 gui = new Gui3();
            gui.go();
        }
    });
}