JTree not updating after

  To: comp.lang.java.gui
My first attempt at implementing drag and drop in Swing has been painful to
say the least. I am trying to setup DnD in a JTree and the first thing I am
attempting is to simply delete the node that is being moved from its parent.
Sounds simple? Well I can't get it to do even that.

The SSCCE attached below shows what I am talking about. I have a method
removeChildNode() which deletes the child node from the parent and notifies
the tree and I know it works because if you run the program the first time
and click on the button then node C is deleted and the tree updates.
However, when I call the same method on the same nodes in the transfer
handler nothing appears to happen so if you run the program again and drag C
on to B for example nothing happens. C should be deleted.

From debug it appears that the model is updating correctly but the tree
itself is not. Can anyone suggest why this might be? Lines 95-98 in the
importData() method seem to be the key but you'll see that the debug there
prints out the correct node data.

Any help much appreciated.

--
And loving it,

-Q
_________________________________________________
Qu0llSixFour@gmail.com
(Replace the "SixFour" with numbers to email me)

import java.awt.BorderLayout;
import java.awt.CardLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Point;
import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.Transferable;
import java.awt.datatransfer.UnsupportedFlavorException;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.IOException;

import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTree;
import javax.swing.TransferHandler;
import javax.swing.WindowConstants;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.DefaultTreeModel;
import javax.swing.tree.TreePath;

public class TreeDnDTestFrame extends JFrame {

 public static final DataFlavor MY_FLAVOR = new DataFlavor(String.class,
"MyFlavor");

 class MyTransferable implements Transferable {
  private final DataFlavor[] flavors = {MY_FLAVOR};
  private DefaultMutableTreeNode data;

  public MyTransferable(final DefaultMutableTreeNode data) {
   this.data = data;
  }

  @Override
  public Object getTransferData(DataFlavor flavor)
   throws UnsupportedFlavorException, IOException {
   if (flavor.equals(flavors[0])) {
    return (Object)data;
   } else {
    throw new UnsupportedFlavorException(flavor);
   }
  }

  @Override
  public DataFlavor[] getTransferDataFlavors() {
   return (DataFlavor[])flavors.clone();
  }

  @Override
  public boolean isDataFlavorSupported(DataFlavor flavor) {
   for (DataFlavor df : flavors) {
    if (df.equals(flavor)) {
     return true;
    }
   }
   return false;
  }
 }

 class MyTransferHandler extends TransferHandler {
  @Override
  protected Transferable createTransferable(JComponent c) {
   JTree tree = (JTree)c;
   Object o = tree.getSelectionPath().getLastPathComponent();
   DefaultMutableTreeNode node = (DefaultMutableTreeNode)o;
   return new MyTransferable(node);
  }

  @Override
  public boolean importData(TransferSupport support) {
   Point dropPoint = support.getDropLocation().getDropPoint();
   JTree tree = (JTree)support.getComponent();
   DefaultTreeModel model = (DefaultTreeModel)tree.getModel();
   TreePath path = tree.getPathForLocation(dropPoint.x, dropPoint.y);
   if (path == null) {
    return false;
   } else {
    DefaultMutableTreeNode target =
(DefaultMutableTreeNode)path.getLastPathComponent();
    DefaultMutableTreeNode data = null;
    try {
     data =
      (DefaultMutableTreeNode)support.getTransferable().getTransferData(MY_FLAVOR);
    }
    catch (UnsupportedFlavorException ufe) {
     return false;
    }
    catch (IOException ioe) {
     return false;
    }
    DefaultMutableTreeNode parent =
(DefaultMutableTreeNode)data.getParent();
    System.out.println("data = " + data + ", target = " + target + ", parent
= " + parent);
    if (parent != null) {
     removeChildNode(parent, data);
    }
   }
   return true;
  }

  @Override
  public boolean canImport(TransferSupport support) {
   return true;
  }

  @Override
  public int getSourceActions(JComponent c) {
   return MOVE;
  }
 }

 private DefaultMutableTreeNode root, a, b, c;
 private JTree tree;

 public TreeDnDTestFrame() {
  setupModel();
  defineGUI();
 }

 public void setupModel() {
  root = new DefaultMutableTreeNode("ROOT");
  a = new DefaultMutableTreeNode("A");
  root.add(a);
  b = new DefaultMutableTreeNode("B");
  root.add(b);
  c = new DefaultMutableTreeNode("C");
  a.add(c);
 }

 public void removeChildNode(DefaultMutableTreeNode parent,
DefaultMutableTreeNode child) {
  final int[] childIndices = {parent.getIndex(child)};
  final Object[] removedChildren = {child};
  parent.remove(child);
  DefaultTreeModel model = (DefaultTreeModel)tree.getModel();
  model.nodesWereRemoved(parent, childIndices, removedChildren);
 }

 public void defineGUI() {
  tree = new JTree();
  JScrollPane scrollPane = new JScrollPane();
  JPanel panel = new JPanel();
  setPreferredSize(new Dimension(800, 600));
  setMinimumSize(new Dimension(800, 600));
  setLayout(new BorderLayout());
  tree = new JTree(root);
  tree.setDragEnabled(true);
  tree.setTransferHandler(new MyTransferHandler());
  scrollPane = new JScrollPane(tree);
  scrollPane.setBorder(BorderFactory.createEmptyBorder());
  JButton b = new JButton("Delete C");
  b.addActionListener(new ActionListener() {
   public void actionPerformed(ActionEvent ae) {
    removeChildNode(a, c);
   }
  });
  panel = new JPanel();
  panel.setLayout(new CardLayout(8, 8));
  panel.add(scrollPane, "Tree");
  add(panel, BorderLayout.CENTER);
  add(b, BorderLayout.SOUTH);
  pack();
  setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
  setLocationRelativeTo(null);
 }

 public static void main(String[] args) {
  EventQueue.invokeLater(new Runnable() {
   public void run() {
    new TreeDnDTestFrame().setVisible(true);
   }
  });
 }
}

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