JTree - drag and drop inside one tree - Java 1.6

Hi,

I am trying to drag and drop tree nodes within the same JTree. I have a code which uses Java 1.2 java.awt.dnd.
I would like to use TransferHandler and newer implementation.
I have found a code which works when JTree is drop target but there is no code where Jtree is drag source and drop target.
Can somone point good link?

BR
Zdenko

http://www.jroller.com/santhosh/date/20050524

Hello "zdenko",

Please read your private messages regarding an important announcement.

Thank you,

Rob

JTrees are complex and there are so many choices/decisons to make and ways of doing things that it's difficult to say much about implementing drag and drop in them. Here's an example, as requested, using the j2se 1.6 improvements. Most of the code in the TransferHandler comes from various parts of the tutorial.
<blockquote>code:

import java.awt.*;
import java.awt.datatransfer.*;
import java.awt.dnd.*;
import java.util.*;
import java.util.List;
import javax.swing.*;
import javax.swing.tree.*;
 
public class TreeDragAndDrop {
    private JScrollPane getContent() {
        JTree tree = new JTree();
        tree.setDragEnabled(true);
        tree.setDropMode(DropMode.ON_OR_INSERT);
        tree.setTransferHandler(new TreeTransferHandler());
        tree.getSelectionModel().setSelectionMode(
                TreeSelectionModel.CONTIGUOUS_TREE_SELECTION);
        expandTree(tree);
        return new JScrollPane(tree);
    }
 
    private void expandTree(JTree tree) {
        DefaultMutableTreeNode root =
            (DefaultMutableTreeNode)tree.getModel().getRoot();
        Enumeration e = root.breadthFirstEnumeration();
        while(e.hasMoreElements()) {
            DefaultMutableTreeNode node =
                (DefaultMutableTreeNode)e.nextElement();
            if(node.isLeaf()) continue;
            int row = tree.getRowForPath(new TreePath(node.getPath()));
            tree.expandRow(row);
        }
    }
 
    public static void main(String[] args) {
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(new TreeDragAndDrop().getContent());
        f.setSize(400,400);
        f.setLocation(200,200);
        f.setVisible(true);
    }
}
 
class TreeTransferHandler extends TransferHandler {
    DataFlavor nodesFlavor;
    DataFlavor[] flavors = new DataFlavor[1];
    DefaultMutableTreeNode[] nodesToRemove;
 
    public TreeTransferHandler() {
        try {
            String mimeType = DataFlavor.javaJVMLocalObjectMimeType +
                              ";class=\"" +
                javax.swing.tree.DefaultMutableTreeNode[].class.getName() +
                              "\"";
            nodesFlavor = new DataFlavor(mimeType);
            flavors[0] = nodesFlavor;
        } catch(ClassNotFoundException e) {
            System.out.println("ClassNotFound: " + e.getMessage());
        }
    }
 
    public boolean canImport(TransferHandler.TransferSupport support) {
        if(!support.isDrop()) {
            return false;
        }
        support.setShowDropLocation(true);
        if(!support.isDataFlavorSupported(nodesFlavor)) {
            return false;
        }
        // Do not allow a drop on the drag source selections.
        JTree.DropLocation dl =
                (JTree.DropLocation)support.getDropLocation();
        JTree tree = (JTree)support.getComponent();
        int dropRow = tree.getRowForPath(dl.getPath());
        int[] selRows = tree.getSelectionRows();
        for(int i = 0; i < selRows.length; i++) {
            if(selRows[i] == dropRow) {
                return false;
            }
        }
        // Do not allow MOVE-action drops if a non-leaf node is
        // selected unless all of its children are also selected.
        int action = support.getDropAction();
        if(action == MOVE) {
            return haveCompleteNode(tree);
        }
        // Do not allow a non-leaf node to be copied to a level
        // which is less than its source level.
        TreePath dest = dl.getPath();
        DefaultMutableTreeNode target =
            (DefaultMutableTreeNode)dest.getLastPathComponent();
        TreePath path = tree.getPathForRow(selRows[0]);
        DefaultMutableTreeNode firstNode =
            (DefaultMutableTreeNode)path.getLastPathComponent();
        if(firstNode.getChildCount() > 0 &&
               target.getLevel() < firstNode.getLevel()) {
            return false;
        }
        return true;
    }
 
    private boolean haveCompleteNode(JTree tree) {
        int[] selRows = tree.getSelectionRows();
        TreePath path = tree.getPathForRow(selRows[0]);
        DefaultMutableTreeNode first =
            (DefaultMutableTreeNode)path.getLastPathComponent();
        int childCount = first.getChildCount();
        // first has children and no children are selected.
        if(childCount > 0 && selRows.length == 1)
            return false;
        // first may have children.
        for(int i = 1; i < selRows.length; i++) {
            path = tree.getPathForRow(selRows[i]);
            DefaultMutableTreeNode next =
                (DefaultMutableTreeNode)path.getLastPathComponent();
            if(first.isNodeChild(next)) {
                // Found a child of first.
                if(childCount > selRows.length-1) {
                    // Not all children of first are selected.
                    return false;
                }
            }
        }
        return true;
    }
 
    protected Transferable createTransferable(JComponent c) {
        JTree tree = (JTree)c;
        TreePath[] paths = tree.getSelectionPaths();
        if(paths != null) {
            // Make up a node array of copies for transfer and
            // another for/of the nodes that will be removed in
            // exportDone after a successful drop.
            List<DefaultMutableTreeNode> copies =
                new ArrayList<DefaultMutableTreeNode>();
            List<DefaultMutableTreeNode> toRemove =
                new ArrayList<DefaultMutableTreeNode>();
            DefaultMutableTreeNode node =
                (DefaultMutableTreeNode)paths[0].getLastPathComponent();
            DefaultMutableTreeNode copy = copy(node);
            copies.add(copy);
            toRemove.add(node);
            for(int i = 1; i < paths.length; i++) {
                DefaultMutableTreeNode next =
                    (DefaultMutableTreeNode)paths[i].getLastPathComponent();
                // Do not allow higher level nodes to be added to list.
                if(next.getLevel() < node.getLevel()) {
                    break;
                } else if(next.getLevel() > node.getLevel()) {  // child node
                    copy.add(copy(next));
                    // node already contains child
                } else {                                        // sibling
                    copies.add(copy(next));
                    toRemove.add(next);
                }
            }
            DefaultMutableTreeNode[] nodes =
                copies.toArray(new DefaultMutableTreeNode[copies.size()]);
            nodesToRemove =
                toRemove.toArray(new DefaultMutableTreeNode[toRemove.size()]);
            return new NodesTransferable(nodes);
        }
        return null;
    }
 
    /** Defensive copy used in createTransferable. */
    private DefaultMutableTreeNode copy(TreeNode node) {
        return new DefaultMutableTreeNode(node);
    }
 
    protected void exportDone(JComponent source, Transferable data, int action) {
        if((action & MOVE) == MOVE) {
            JTree tree = (JTree)source;
            DefaultTreeModel model = (DefaultTreeModel)tree.getModel();
            // Remove nodes saved in nodesToRemove in createTransferable.
            for(int i = 0; i < nodesToRemove.length; i++) {
                model.removeNodeFromParent(nodesToRemove[i]);
            }
        }
    }
 
    public int getSourceActions(JComponent c) {
        return COPY_OR_MOVE;
    }
 
    public boolean importData(TransferHandler.TransferSupport support) {
        if(!canImport(support)) {
            return false;
        }
        // Extract transfer data.
        DefaultMutableTreeNode[] nodes = null;
        try {
            Transferable t = support.getTransferable();
            nodes = (DefaultMutableTreeNode[])t.getTransferData(nodesFlavor);
        } catch(UnsupportedFlavorException ufe) {
            System.out.println("UnsupportedFlavor: " + ufe.getMessage());
        } catch(java.io.IOException ioe) {
            System.out.println("I/O error: " + ioe.getMessage());
        }
        // Get drop location info.
        JTree.DropLocation dl =
                (JTree.DropLocation)support.getDropLocation();
        int childIndex = dl.getChildIndex();
        TreePath dest = dl.getPath();
        DefaultMutableTreeNode parent =
            (DefaultMutableTreeNode)dest.getLastPathComponent();
        JTree tree = (JTree)support.getComponent();
        DefaultTreeModel model = (DefaultTreeModel)tree.getModel();
        // Configure for drop mode.
        int index = childIndex;    // DropMode.INSERT
        if(childIndex == -1) {     // DropMode.ON
            index = parent.getChildCount();
        }
        // Add data to model.
        for(int i = 0; i < nodes.length; i++) {
            model.insertNodeInto(nodes[i], parent, index++);
        }
        return true;
    }
 
    public String toString() {
        return getClass().getName();
    }
 
    public class NodesTransferable implements Transferable {
        DefaultMutableTreeNode[] nodes;
 
        public NodesTransferable(DefaultMutableTreeNode[] nodes) {
            this.nodes = nodes;
         }
 
        public Object getTransferData(DataFlavor flavor)
                                 throws UnsupportedFlavorException {
            if(!isDataFlavorSupported(flavor))
                throw new UnsupportedFlavorException(flavor);
            return nodes;
        }
 
        public DataFlavor[] getTransferDataFlavors() {
            return flavors;
        }
 
        public boolean isDataFlavorSupported(DataFlavor flavor) {
            return nodesFlavor.equals(flavor);
        }
    }
}

</pre>

</blockquote>

Wow, thanks Craig!
Your code was a giant help to me to see the plentyful yapping (sorry for the sarcasm, it was of course very helpful too!) of the tutorials put together and made work by someone!

I myself was struggling to see my tree implement DnD successfully until I saw your code above.

I'd like to ask yo, if I might use part of your code in my customTreeDataHandler class? (As your code works, and mine not

... looks like my understanding of dnd still didn't reach a level where I can actually make it do what I'd like it to do

)

Thanks for your answer in advance!

use part of your code in my customTreeDataHandler class
Yes, of course.

Hi Craig Wood,

I too have a problem in JTree that is I want to move the JTree nodes to another JTree without changing its structure. but only the selected nodes should move. Help me in this issue.

Thank you.

Melki Joe wrote:Hi Craig Wood,

I too have a problem in JTree that is I want to move the JTree nodes to another JTree without changing its structure. but only the selected nodes should move. Help me in this issue.

Thank you.

Hi Melki Joe .
See my solution

That's quite some kick, Evgeny, and I'm sorry to say that its intended purpose is not achieved either: Melki hasn't posted since December 16th.

Evgeny Krylov wrote:

Melki Joe wrote:Hi Craig Wood,

I too have a problem in JTree that is I want to move the JTree nodes to another JTree without changing its structure. but only the selected nodes should move. Help me in this issue.

Thank you.

Hi Melki Joe .
See my solution

Your code might be of public interest, if only it were compilable. Here ist only one example of many broken statements in your code:

Andre Uhres wrote:

Evgeny Krylov wrote:

Melki Joe wrote:Hi Craig Wood,

I too have a problem in JTree that is I want to move the JTree nodes to another JTree without changing its structure. but only the selected nodes should move. Help me in this issue.

Thank you.

Hi Melki Joe .
See my solution

Your code might be of public interest, if only it were compilable. Here ist only one example of many broken statements in your code:
for(int i=0;i vpath.add(path[i].toString()); }

Andre, thanks for comment.
It was my bug of my web-publishing tool.
Now working
my solution

Thanks Craig, your code was exactly what I was looking for.

Zombie alert.

We worry a lot less about old threads than we used to. The zombie FAQ has been changed.

Thanks for the heads up! I hadn't looked at that page in a long time.

Very nice illustration and almost perfect! Thanks, Craig! It works but there is nevertheless a subtle bug (in the method below)

As it is, as you multiply the moves, it repeatedly wraps nodes into a new node (instead of only its userObject).

A correct implementation would be, e.g.,

Based on this working example, I have cleaned up a messy class of mine (with more generic purposes) that had become unmaintainable.

A big thank again !
Alain

Well, actually, I have used

(Don't remember exactly why)

Alain

The problem with the TreeTransferHandler is that if i drag an element of the JTree into another position in the same level, the element will be removed from the JList and will be lost.
If the element is dropped into the same level of the JTree, the element should not be removed from the JTree but leaved in the location it was without doing anything ...