JLabel is not moving properly using mouse motion listener, Why?

Question

Whenever I draggs mouse I need to move JLabel accordingly.
Why it shows multiple JLabel while dragging and not showing the component at proper location ?

public class Mover extends JFrame 
{

private JPanel jPanel;
private JLabel jLabel1;
private JLabel jLabel2;
private int myXX = 0;
private int myYY = 0;

public Mover() {
    setSize(500, 500);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    jPanel = new JPanel(null);
    jLabel1 = new JLabel("label one");
    jLabel2 = new JLabel("label two");

    jLabel1.setBounds(100, 100, 100, 100);
    jLabel2.setBounds(100, 100, 100, 100);
    jLabel1.addMouseMotionListener(new MouseMotionListener() {

        @Override
        public void mouseMoved(MouseEvent e) {
        }

        @Override
        public void mouseDragged(MouseEvent e) {
            System.out.println("Label One");
            myXX = e.getX() - (jLabel1.getWidth() / 2);
            myYY = e.getY() - (jLabel1.getHeight() / 2);
            jLabel1.setLocation(myXX, myYY);
            repaint();
        }
    });
    jLabel2.addMouseMotionListener(new MouseMotionListener() {

        @Override
        public void mouseMoved(MouseEvent e) {
        }

        @Override
        public void mouseDragged(MouseEvent e) {
            System.out.println("Label Two");

            myXX = e.getX() - (jLabel2.getWidth() / 2);
            myYY = e.getY() - (jLabel2.getHeight() / 2);
            jLabel2.setLocation(myXX, myYY);
            repaint();
        }
    });
    jPanel.add(jLabel1);
    jPanel.add(jLabel2);
    add(jPanel);
    repaint();
    revalidate();
    setVisible(true);
}

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

Is there any perfact solution of this problem ?
obviously Thanks in advance.

The `MouseEvent` is based on the local component context from which it was generated, that is, the x/y position is relative to the label's x/y position — MadProgrammer, Oct 15 '14 at 05:45
No point calling `revalidate` when you have no layout manager, there's nothing to revalidate... — MadProgrammer, Oct 15 '14 at 05:47
Ohk but can we move the position of lable according to the mouse moves ? — Gopal00005, Oct 15 '14 at 05:48
Yes, you need to translate the source point to it's parent context...see answer for examples... — MadProgrammer, Oct 15 '14 at 05:55

score 2 · Accepted Answer · answered Oct 15 '14 at 05:52

The MouseEvent information is contextual to the component that generated the event, in this case, the labels.

This means that 0x0 is actually the top/left corner of the label. You need to convert the point information of the event to it's parent context, for example...

Point p = e.getPoint();
p = SwingUtilities.convertPoint(e.getComponent(), p, e.getComponent().getParent());

You, also, don't need to make myXX or myYY instance fields, as they only ever really have context to the mouse event that is driving them.

You should also take a look at Initial Threads and make sure you're launching your program within the context of the Event Dispatching Thread...

You also don't need to create a separate listener for each component, with just a little bit of clever use of the available information from the MouseEvent you can use a single listener for all the components and reduce the code duplication...

import java.awt.Component;
import java.awt.EventQueue;
import java.awt.Point;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Mover extends JFrame {

    private JPanel jPanel;
    private JLabel jLabel1;
    private JLabel jLabel2;

    public Mover() {
        setSize(500, 500);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        jPanel = new JPanel(null);
        jLabel1 = new JLabel("label one");
        jLabel2 = new JLabel("label two");

        jLabel1.setBounds(100, 100, 100, 100);
        jLabel2.setBounds(100, 100, 100, 100);

        MouseMotionListener mover = new MouseMotionListener() {

            @Override
            public void mouseMoved(MouseEvent e) {
            }

            @Override
            public void mouseDragged(MouseEvent e) {
                System.out.println("Label One");

                Component child = e.getComponent();
                Point p = e.getPoint();
                p = SwingUtilities.convertPoint(e.getComponent(), p, e.getComponent().getParent());

                int myXX = p.x - (child.getWidth() / 2);
                int myYY = p.y - (child.getHeight() / 2);
                child.setLocation(myXX, myYY);
                repaint();
            }
        };

        jLabel1.addMouseMotionListener(mover);
        jLabel2.addMouseMotionListener(mover);

        jPanel.add(jLabel1);
        jPanel.add(jLabel2);
        add(jPanel);
        setVisible(true);
    }

    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();
                }

                new Mover();
            }
        });
    }
}

I'd be doing you a disservice if I didn't point out that extending directly from a top level container like JFrame is bad practice and will lock you into a single use container, making it difficult to re-use the container in the future or add it to other containers should you so wish to...besides, you're not really adding any functionality to it...

Oh wow! but can you tell me UIManager is compulsory to add in swing ? — Gopal00005, Oct 15 '14 at 05:57
Yep I got it but is it required to make child component in MouseEvent ? — Gopal00005, Oct 15 '14 at 06:00
Nah, it's just simpler then having to repeatedly call `MouseEvent#getComponent`.... — MadProgrammer, Oct 15 '14 at 06:03
+1 for your quick response and accepted because it's damn real solution... :) — Gopal00005, Oct 15 '14 at 06:05

JLabel is not moving properly using mouse motion listener, Why?

1 Answers1

Linked