Question

I have class JLabelExtended, which extends class javax.swing.JLabel.
I extend it, because I want to add property dragging using mouse.
Here is my code:

public class JLabelExtended extends JLabel {
private MouseMotionAdapter mouseMotionAdapter;

private JLabelExtended jLabelExtended;

public LabelEasy(String text) {
    super(text);
    jLabelExtended = this;

    mouseMotionAdapter = new MouseMotionAdapter() {
        @Override
        public void mouseDragged(MouseEvent e) {
            System.out.println(e.getX() + "  :   " + e.getY());
            jLabelExtended.setLocation(e.getX(), e.getY()
            );
        }
    };

    jLabelExtended.addMouseMotionListener(mouseMotionAdapter);
}

}

This is console part after label dragged:

163  :   163
144  :   -87
163  :   162
144  :   -88
163  :   161
144  :   -89

I have several questions:

1. Why e.getY() takes negative results?

2. When I drag my label there are appeares copy of label which drags near my label. How can I fix it?

3. When I drag my label, it drags very slowly.For example: when I move my cursor on 10 points my label moves only on 5 point. How can I fix it?

Thanks in advance

Here are else one way to extend JLabel:

public class LabelEasy extends JLabel {
private MouseAdapter moveMouseAdapter;
private MouseMotionAdapter mouseMotionAdapter;

private LabelEasy jLabelExtended;

private int xAdjustment, yAdjustment;
Boolean count = false;

public LabelEasy(String text) {
    super(text);
    jLabelExtended = this;

    moveMouseAdapter = new MouseAdapter() {
        @Override
        public void mouseClicked(MouseEvent e) {
            if (e.getButton() == 1) {
                xAdjustment = e.getX();
                yAdjustment = e.getY();
            }
        }
    };

    mouseMotionAdapter = new MouseMotionAdapter() {
        @Override
        public void mouseDragged(MouseEvent e) {
            if (count) {
                System.out.println(e.getX() + "  :   " + e.getY());
                jLabelExtended.setLocation(xAdjustment + e.getX(), yAdjustment + e.getY());
                count = false;
            } else {
                count = true;
            }
            ;
        }
    };

    jLabelExtended.addMouseMotionListener(mouseMotionAdapter);
    jLabelExtended.addMouseListener(moveMouseAdapter);
}

}

But it works like previous variant.

Answer 1

I think you’re doing it wrong. The MouseMotionListener is added to the JLabel and its location is relative to the JLabel, not the Container which holds the JLabel, so the information is useless to help you drag it. You may wish to use a MouseAdapter and add it both as a MouseListener and a MouseMotionListener. On mousePressed, get the location of the JLabel and the mouse relative to the screen and then use that for your dragging on mouseDragged. Myself, I wouldn’t extend JLabel to do this but would rather just use a regular JLabel, but that’s my preference.

Edit: it worked better for me when I dealt with the mouse’s position relative to the screen (by calling getLocationOnScreen) and the JLabel’s position relative to its Container (by calling getLocation). For e.g.,

import java.awt.*;
import java.awt.event.*;
import java.util.Random;
import javax.swing.*;

public class DragLabelEg {
    private static final String[] LABEL_STRINGS = { "Do", "Re", "Me", "Fa",
            "So", "La", "Ti" };
    private static final int HEIGHT = 400;
    private static final int WIDTH = 600;
    private static final Dimension MAIN_PANEL_SIZE = new Dimension(WIDTH,
            HEIGHT);
    private static final int LBL_WIDTH = 60;
    private static final int LBL_HEIGHT = 40;
    private static final Dimension LABEL_SIZE = new Dimension(LBL_WIDTH,
            LBL_HEIGHT);
    private JPanel mainPanel = new JPanel();
    private Random random = new Random();

    public DragLabelEg() {
        mainPanel.setPreferredSize(MAIN_PANEL_SIZE);
        mainPanel.setLayout(null);

        MyMouseAdapter myMouseAdapter = new MyMouseAdapter();
        for (int i = 0; i < LABEL_STRINGS.length; i++) {
            JLabel label = new JLabel(LABEL_STRINGS[i], SwingConstants.CENTER);
            label.setSize(LABEL_SIZE);
            label.setOpaque(true);
            label.setLocation(random.nextInt(WIDTH - LBL_WIDTH),
                    random.nextInt(HEIGHT - LBL_HEIGHT));
            label.setBackground(new Color(150 + random.nextInt(105),
                    150 + random.nextInt(105), 150 + random.nextInt(105)));
            label.addMouseListener(myMouseAdapter);
            label.addMouseMotionListener(myMouseAdapter);

            mainPanel.add(label);
        }
    }

    public JComponent getMainPanel() {
        return mainPanel;
    }

    private class MyMouseAdapter extends MouseAdapter {
        private Point initLabelLocation = null;
        private Point initMouseLocationOnScreen = null;

        @Override
        public void mousePressed(MouseEvent e) {
            JLabel label = (JLabel)e.getSource();
            // get label's initial location relative to its container
            initLabelLocation = label.getLocation();

            // get Mouse's initial location relative to the screen 
            initMouseLocationOnScreen = e.getLocationOnScreen();
        }

        @Override
        public void mouseReleased(MouseEvent e) {
            initLabelLocation = null;
            initMouseLocationOnScreen = null;
        }

        @Override
        public void mouseDragged(MouseEvent e) {
            // if not dragging a JLabel
            if (initLabelLocation == null || initMouseLocationOnScreen == null) {
                return;
            }
            JLabel label = (JLabel)e.getSource();

            // get mouse's new location relative to the screen
            Point mouseLocation = e.getLocationOnScreen();

            // and see how this differs from the initial location.
            int deltaX = mouseLocation.x - initMouseLocationOnScreen.x;
            int deltaY = mouseLocation.y - initMouseLocationOnScreen.y;

            // change label's position by the same difference, the "delta" vector
            int labelX = initLabelLocation.x + deltaX;
            int labelY = initLabelLocation.y + deltaY;

            label.setLocation(labelX, labelY);
        }
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createGui();
            }
        });
    }

    private static void createGui() {
        JFrame frame = new JFrame("App");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(new DragLabelEg().getMainPanel());
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
}