java-FLowLayout（）中的两个图像在移动时将消失

Question

I have the following code that produces two seperate .pngs on the screen. These .pngs are meant to be moved by the mouse and all is working well except for when they are dragged the are seemingly under some type of layer and the disappear when dragged more than an inch. Any advice so appreciated.

 import java.awt.*;
import javax.swing.*;
import java.awt.event.MouseEvent;
import java.awt.event.MouseAdapter;

public class TestMouseDrag {

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

public TestMouseDrag() {
    EventQueue.invokeLater(new Runnable() {
        @Override
        public void run() {


            JFrame frame = new JFrame();
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setLayout(new FlowLayout());
            frame.add(new DragMyIcon("C:\\Users\\anon\\Desktop\\Hobbit.png"));
            frame.add(new DragMyIcon("C:\\Users\\anon\\Desktop\\alien.png"));

            frame.setSize(800,800);

            frame.setVisible(true);
        }
    });
}

public class DragMyIcon extends JPanel {

    public static final long serialVersionUID = 172L;
    private JLabel label;

    public DragMyIcon(String path) {


        ImageIcon icon = null;

        icon = new ImageIcon(path);

        label = new JLabel(icon);



        add(label);

        MouseHandler handler = new MouseHandler();
        label.addMouseListener(handler);
        label.addMouseMotionListener(handler);

    }

}

protected class MouseHandler extends MouseAdapter {

    private boolean active = false;
    private int xDisp;
    private int yDisp;

    @Override
    public void mousePressed(MouseEvent e) {
        active = true;
        JLabel label = (JLabel) e.getComponent();

        xDisp = e.getPoint().x - label.getLocation().x;
        yDisp = e.getPoint().y - label.getLocation().y;

        label.setCursor(Cursor.getPredefinedCursor(Cursor.MOVE_CURSOR));
    }

    @Override
    public void mouseReleased(MouseEvent e) {
        active = false;
        JLabel label = (JLabel) e.getComponent();
        label.setCursor(Cursor.getPredefinedCursor(Cursor.DEFAULT_CURSOR));
    }

    @Override
    public void mouseDragged(MouseEvent e) {
        if (active) {
            JLabel label = (JLabel) e.getComponent();
            Point point = e.getPoint();
            label.setLocation(point.x - xDisp, point.y - yDisp);
            label.invalidate();
            label.repaint();

        }
    }

    @Override
    public void mouseMoved(MouseEvent e) {
    }
}}

Answer 1

Just @Override getPreferredSize in you JPanel and just pack() your frame, instead of setting the size and it works fine.

   frame.pack();
   ...

   public class DragMyIcon extends JPanel {
       ...
       @Override
       public Dimension getPreferredSize() {
           return new Dimension(400, 600);
       }
   }

The thing about this remember though, these are two separate panels (as you're creating two separate instances of DragMyIcon ), so you will only be able to move the label the extent of the containing panel. If you want to be able to move them all over the screen, you need to add them to the same panel.