What does this parameter do ? (d&d)

Question

Hi there,
I'm working on some d&d code. When I drag, I want to see an image and not only the drag cursor.
There is a parameter in DragGestureEvent where I can put an Image. Is this the image that'll be visually dragged on screen ?? My code:
    e.startDrag(DragSource.DefaultCopyDrop,dragImage, new Point(10,10), new StringSelection("ARF!!"), this); dragImage is an instance of image.
This doesn't show the image. Is there something wrong ?

Answer 1

On Windows, if you want to simulate the drag of the selected image, you have to do it in the DropTargetListener like this :
It is an inner class of the component you want to drag in (Called here MyDraggableComponent : in most cases it's a JTree).
In this component there is an attribute like this :
BufferedImage buffImage;
     final class MyDropTargetListener implements DropTargetListener {
          private Rectangle rect2D = new Rectangle();
          public void dragEnter(DropTargetDragEvent dtde) {
               Point pt = dtde.getLocation();
               paintImmediately(rect2D.getBounds());
               rect2D.setRect((int) pt.getX(),(int) pt.getY(),buffImage.getWidth(),buffImage.getHeight());
               ((Graphics2D) getGraphics()).drawImage(buffImage,(int) pt.getX(),(int) pt.getY(),MyDraggableComponent.this);
          public void dragExit(DropTargetEvent dte) {
               paintImmediately(rect2D.getBounds());
          public void dragOver(DropTargetDragEvent dtde) {
               Point pt = dtde.getLocation();
               paintImmediately(rect2D.getBounds());
               rect2D.setRect((int) pt.getX(),(int) pt.getY(),buffImage.getWidth(),buffImage.getHeight());
               ((Graphics2D) getGraphics()).drawImage(buffImage,(int) pt.getX(),(int) pt.getY(),MyDraggableComponent.this);
          public void dropActionChanged(DropTargetDragEvent dtde) {
               Point pt = dtde.getLocation();
               paintImmediately(rect2D.getBounds());
               rect2D.setRect((int) pt.getX(),(int) pt.getY(),buffImage.getWidth(),buffImage.getHeight());
               ((Graphics2D) getGraphics()).drawImage(buffImage,(int) pt.getX(),(int) pt.getY(),MyDraggableComponent.this);
          public void drop(DropTargetDropEvent dtde) {
               Point pt = dtde.getLocation();
               paintImmediately(rect2D.getBounds());
               rect2D.setRect((int) pt.getX(),(int) pt.getY(),buffImage.getWidth(),buffImage.getHeight());
               ((Graphics2D) getGraphics()).drawImage(buffImage,(int) pt.getX(),(int) pt.getY(),MyDraggableComponent.this);
     }You have to create the buffered image in the method dragGestureRecognized od the DragGestureListener.
For example a DragGestureListener in a JTree called MyDraggableComponent :
     final class TreeDragGestureListener implements DragGestureListener {
          DragSourceListener tdsl;
          public TreeDragGestureListener(DragSourceListener dsl) {
               this.dsl = dsl;
          public void dragGestureRecognized(DragGestureEvent dge) {
               TreePath path = getSelectionPath(); // getselectionpath
               if (path != null) {
                    DefaultMutableTreeNode selectednode = (DefaultMutableTreeNode)path.getLastPathComponent();
                    Rectangle pathBounds = getPathBounds(path); //getpathbounds of selectionpath
                    JLabel lbl = (JLabel)getCellRenderer().getTreeCellRendererComponent(MyDraggableComponent.this, selectednode, false , isExpanded(path),((DefaultTreeModel)getModel()).isLeaf(path.getLastPathComponent()), 0,false);//returning the label
                    lbl.setBounds(pathBounds);//setting bounds to lbl
                    buffImage = new BufferedImage(lbl.getWidth(), lbl.getHeight(), BufferedImage.TYPE_INT_ARGB_PRE);//buffered image reference passing the label's ht and width
                    Graphics2D graphics = buffImage.createGraphics();//creating the graphics for buffered image
                    graphics.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, 0.5f));     //Sets the Composite for the Graphics2D context
                    lbl.setOpaque(false);
                    lbl.paint(graphics); //painting the label on the graphics of the buffered image
                    graphics.dispose();
                    dragSource.startDrag(dge, DragSource.DefaultMoveNoDrop , buffImage, new Point(0,0), new TransferableNode(selectednode), dsl);               
     }I hope this helps,
Denis