Create a custom drag ghost image

• download example.jar
• download src.zip
• repository

Code

class ListItemTransferHandler extends TransferHandler {
  @Override public int getSourceActions(JComponent c) {
    System.out.println("getSourceActions");
    if (!(c instanceof JList)) {
      return NONE;
    }
    JList source = (JList) c;
    Point pt;
    if (compact) {
      int w = source.getFixedCellWidth();
      int h = source.getFixedCellHeight() - 20; //TODO
      setDragImage(createCompactDragImage(source, w, h));
      pt = new Point(w / 2, h);
    } else {
      setDragImage(createDragImage(source));
      pt = c.getMousePosition();
    }
    if (pt != null) {
      setDragImageOffset(pt);
    }
    return MOVE; //TransferHandler.COPY_OR_MOVE;
  }
  private static BufferedImage createDragImage(JList source) {
    int w = source.getWidth();
    int h = source.getHeight();
    BufferedImage bi = new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);
    Graphics g = bi.getGraphics();
    DefaultListCellRenderer renderer =
      (DefaultListCellRenderer) source.getCellRenderer();
    for (int i : source.getSelectedIndices()) {
      Component c = renderer.getListCellRendererComponent(
          source, source.getModel().getElementAt(i), i, false, false);
      Rectangle rect = source.getCellBounds(i, i);
      SwingUtilities.paintComponent(g, c, source, rect);
    }
    g.dispose();
    return bi;
  }
  private BufferedImage createCompactDragImage(JList source, int w, int h) {
    BufferedImage br = null;
    if (w > 0 && h > 0) {
      br = source.getGraphicsConfiguration().createCompatibleImage(
          w, h, Transparency.TRANSLUCENT);
    } else {
      return null;
    }
    int[] selectedIndices = source.getSelectedIndices();
    int length = selectedIndices.length;
    Graphics g = br.getGraphics();
    DefaultListCellRenderer renderer =
      (DefaultListCellRenderer) source.getCellRenderer();
    int idx = selectedIndices[0];
    Object valueAt = source.getModel().getElementAt(idx);
    Component c = renderer.getListCellRendererComponent(
        source, valueAt, idx, false, false);
    Rectangle rect = source.getCellBounds(idx, idx);
    SwingUtilities.paintComponent(g, c, source, 0, 0, rect.width, rect.height);
    if (length > 1) {
      LABEL.setText(String.valueOf(length));
      Dimension d = LABEL.getPreferredSize();
      SwingUtilities.paintComponent(
          g, LABEL, source, (w - d.width) / 2, (h - d.height) / 2, d.width, d.height);
    }
    g.dispose();
    br.coerceData(true);
    return br;
  }
//...

References

• Create a custom drag ghost image(Japanese)