java - Drag and Drop nodes in JTree

Question

I am having difficulty creating a JTree that allows the nodes to be reorganized by dragging and dropping them in the JTree. This seems like it should be relatively simple. I have looked at examples online, but I can not seem to implement it in my own code.

For example, this provided by sun allows for dragging between different components into the tree, but not from within the tree itself.

And I have also found this that allows you to drag text into the JTree, but not within the tree.

import java.awt.*;
import java.awt.datatransfer.*;
import java.awt.event.*;
import java.io.*;
import javax.swing.*;
import javax.swing.tree.*;

public class DndTree {

    public static void main(String args[]) {
        Runnable runner = new Runnable()  {

            public void run() {
                JFrame f = new JFrame("D-n-D JTree");
                f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

                JPanel top = new JPanel(new BorderLayout());
                JLabel dragLabel = new JLabel("Drag me:");
                JTextField text = new JTextField();
                text.setDragEnabled(true);
                top.add(dragLabel, BorderLayout.WEST);
                top.add(text, BorderLayout.CENTER);
                f.add(top, BorderLayout.NORTH);

                final JTree tree = new JTree();
                final DefaultTreeModel model = (DefaultTreeModel) tree.getModel();
                tree.setTransferHandler(new TransferHandler()  {

                    public boolean canImport(TransferHandler.TransferSupport support) {
                        if (!support.isDataFlavorSupported(DataFlavor.stringFlavor)
                                || !support.isDrop()) {
                            return false;
                        }

                        JTree.DropLocation dropLocation =
                                (JTree.DropLocation) support.getDropLocation();

                        return dropLocation.getPath() != null;
                    }

                    public boolean importData(TransferHandler.TransferSupport support) {
                        if (!canImport(support)) {
                            return false;
                        }

                        JTree.DropLocation dropLocation =
                                (JTree.DropLocation) support.getDropLocation();

                        TreePath path = dropLocation.getPath();

                        Transferable transferable = support.getTransferable();

                        String transferData;
                        try {
                            transferData = (String) transferable.getTransferData(
                                    DataFlavor.stringFlavor);
                        } catch (IOException e) {
                            return false;
                        } catch (UnsupportedFlavorException e) {
                            return false;
                        }

                        int childIndex = dropLocation.getChildIndex();
                        if (childIndex == -1) {
                            childIndex = model.getChildCount(path.getLastPathComponent());
                        }

                        DefaultMutableTreeNode newNode =
                                new DefaultMutableTreeNode(transferData);
                        DefaultMutableTreeNode parentNode =
                                (DefaultMutableTreeNode) path.getLastPathComponent();
                        model.insertNodeInto(newNode, parentNode, childIndex);

                        TreePath newPath = path.pathByAddingChild(newNode);
                        tree.makeVisible(newPath);
                        tree.scrollRectToVisible(tree.getPathBounds(newPath));

                        return true;
                    }
                });

                JScrollPane pane = new JScrollPane(tree);
                f.add(pane, BorderLayout.CENTER);

                JPanel bottom = new JPanel();
                JLabel comboLabel = new JLabel("DropMode");
                String options[] = {"USE_SELECTION",
                    "ON", "INSERT", "ON_OR_INSERT"
                };
                final DropMode mode[] = {DropMode.USE_SELECTION,
                    DropMode.ON, DropMode.INSERT, DropMode.ON_OR_INSERT};
                final JComboBox combo = new JComboBox(options);
                combo.addActionListener(new ActionListener()  {

                    public void actionPerformed(ActionEvent e) {
                        int selectedIndex = combo.getSelectedIndex();
                        tree.setDropMode(mode[selectedIndex]);
                    }
                });
                bottom.add(comboLabel);
                bottom.add(combo);
                f.add(bottom, BorderLayout.SOUTH);
                f.setSize(300, 400);
                f.setVisible(true);
            }
        };
        EventQueue.invokeLater(runner);
    }
}

Any references or suggestions would be great. Thanks

Answer 1

Haven't done this before, but a quick google search turned up the same question here: http://www.coderanch.com/t/346509/GUI/java/JTree-drag-drop-inside-one it has a working implementation that you can look at.

Here is the relevant code that Craig Wood posted:

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);
        }
    }
}