Swing: Creating a draggable component...?

Question

I searched the web for examples of draggable Swing components, but I found either incomplete or non-working examples.

What I need is a Swing component that can be dragged by the mouse inside an other component. While being dragged, it should already change its position, not just 'jump' to its destination.

I would appreciate examples which work without non-standard APIs.

Thank you.

Answer 1

I propose a simple, but well-working solution, found out by myself ;)

What do I do?

• When mouse is pressed, I record the cursor's position on screen, and the component's position.
• When mouse is dragged, I calculate the difference between new and old cursor's position on screen, and move the component by this difference.

Tested with latest JDK 6 unter Linux (OpenSuse, KDE3),
but hey, it's Java Swing, should work equally everywhere.

Here goes the code:

import java.awt.*; import java.awt.event.*; import javax.swing.*; import javax.swing.border.*;  public class MyDraggableComponent     extends JComponent {    private volatile int screenX = 0;   private volatile int screenY = 0;   private volatile int myX = 0;   private volatile int myY = 0;    public MyDraggableComponent() {     setBorder(new LineBorder(Color.BLUE, 3));     setBackground(Color.WHITE);     setBounds(0, 0, 100, 100);     setOpaque(false);      addMouseListener(new MouseListener() {        @Override       public void mouseClicked(MouseEvent e) { }        @Override       public void mousePressed(MouseEvent e) {         screenX = e.getXOnScreen();         screenY = e.getYOnScreen();          myX = getX();         myY = getY();       }        @Override       public void mouseReleased(MouseEvent e) { }        @Override       public void mouseEntered(MouseEvent e) { }        @Override       public void mouseExited(MouseEvent e) { }      });     addMouseMotionListener(new MouseMotionListener() {        @Override       public void mouseDragged(MouseEvent e) {         int deltaX = e.getXOnScreen() - screenX;         int deltaY = e.getYOnScreen() - screenY;          setLocation(myX + deltaX, myY + deltaY);       }        @Override       public void mouseMoved(MouseEvent e) { }      });   }  }  public class Main {    public static void main(String[] args) {     JFrame f = new JFrame("Swing Hello World");      // by doing this, we prevent Swing from resizing     // our nice component     f.setLayout(null);      MyDraggableComponent mc = new MyDraggableComponent();     f.add(mc);      f.setSize(500, 500);      f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);     f.setVisible(true);   }  }