NullPointerException in TreeModel after removeNodeFromParent()

[Anil Philip]

Hello,
I have been stuck for more than a few days on this problem. Tried to get help elsewhere, without luck - wondered if anyone here would have insight into this. I promise I shall update the forum if I get a solution.

if (node.getParent() != null)
treeModel.removeNodeFromParent(node);

Please Note that node is NOT null otherwise NP would have been thrown in the node.getParent(). I am mystified to get this NP exception within the Swing lib. Any insights?
thanks,
Anil

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at javax.swing.plaf.basic.BasicTreeUI.completeEditing(Unknown Source)
at javax.swing.plaf.basic.BasicTreeUI.completeEditing(Unknown Source)
at javax.swing.plaf.basic.BasicTreeUI$Handler.valueChanged(Unknown Source)
at javax.swing.tree.DefaultTreeSelectionModel.fireValueChanged(Unknown Source)
at javax.swing.tree.DefaultTreeSelectionModel.notifyPathChange(Unknown Source)
at javax.swing.tree.DefaultTreeSelectionModel.removeSelectionPaths(Unknown Source)
at javax.swing.JTree.removeDescendantSelectedPaths(Unknown Source)
at javax.swing.JTree.removeDescendantSelectedPaths(Unknown Source)
at javax.swing.JTree$TreeModelHandler.treeNodesRemoved(Unknown Source)
at javax.swing.tree.DefaultTreeModel.fireTreeNodesRemoved(Unknown Source)
at javax.swing.tree.DefaultTreeModel.nodesWereRemoved(Unknown Source)
at javax.swing.tree.DefaultTreeModel.removeNodeFromParent(Unknown Source)

----------

I wonder if it may be because when I create the JPanel which contains the tree, I dont have the root node created. So I instantiate the tree model with null;

treeModel = new DefaultTreeModel(null);

later on, when the root node is available, I use

treeModel.setRoot(root);

This works fine during display of the tree, but when I try to remove the node, for some reason, it may not have updated the root value (?). Just guessing... But I wonder how to fix it. Can I add the Scroll Pane with null first and then with the actual JTree later on? (there is no method in JScrollPane to reset the Component)

public TreeView() {
super(new BorderLayout());
treeModel = new DefaultTreeModel(null);
tree = new JTree(treeModel);
...
JScrollPane scrollPane = new JScrollPane(tree);
add(scrollPane,BorderLayout.CENTER);
}

-----------
When I try to remove the node differently - using the methods in DefaultMutableTreeNode,

if (node.getParent() != null) {
TreeNode parent = node.getParent();
int i = parent.getIndex(node);
node.removeFromParent();
treeModel.nodesWereRemoved(parent,new int[]{i},new Object[]{node});
}

I still get this exception in the treeModel.nodesWereRemoved() call.
Any insight?
thanks,
Anil

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at javax.swing.plaf.basic.BasicTreeUI.completeEditing(Unknown Source)
at javax.swing.plaf.basic.BasicTreeUI.completeEditing(Unknown Source)
at javax.swing.plaf.basic.BasicTreeUI$Handler.valueChanged(Unknown Source)
at javax.swing.tree.DefaultTreeSelectionModel.fireValueChanged(Unknown Source)
at javax.swing.tree.DefaultTreeSelectionModel.notifyPathChange(Unknown Source)
at javax.swing.tree.DefaultTreeSelectionModel.removeSelectionPaths(Unknown Source)
at javax.swing.JTree.removeDescendantSelectedPaths(Unknown Source)getTreeCellRendererComponent:0 ()
 
at javax.swing.JTree.removeDescendantSelectedPaths(Unknown Source)
at javax.swing.JTree$TreeModelHandler.treeNodesRemoved(Unknown Source)
at javax.swing.tree.DefaultTreeModel.fireTreeNodesRemoved(Unknown Source)
at javax.swing.tree.DefaultTreeModel.nodesWereRemoved(Unknown Source)
 

[Anand Loni]

Hi,

before removing node from parent u have to find if it has any sibling or not if no sibling then assign sibling as parent.

***********
public MutableTreeNode getSibling(DefaultMutableTreeNode current)
{
//get previous sibling if any
MutableTreeNode previous=current.getPreviousSibling();
if(previous==null)
{
previous=current.getNextSibling();
}
return previous;
}

************

in delete function code do the following:

**********

MutableTreeNode selected=(MutableTreeNode)tree.getLastSelectedPathComponent();
MutableTreeNode parent = (MutableTreeNode) selected.getParent();
MutableTreeNode sibling= getSibling(selected);
//if no sibling then assign parent to it
if(sibling==null)
{
sibling = parent;
}
treeModel.removeNodeFromParent(selected);
treeModel.reload();
*********************

Hope this will work

Regards,

[Anil Philip]

Originally posted by Anand Loni:
[QB]Hi,

before removing node from parent u have to find if it has any sibling or not if no sibling then assign sibling as parent.

if(sibling==null)
{
sibling = parent;
}
treeModel.removeNodeFromParent(selected);
treeModel.reload();
[QB]

Sorry, but this doesnt make sense. What does that code do?
-
Anil

[Anil Philip]

I have reproduced the problem in the toy program below. Click on any button, you will see the exception at bottom.

import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.EventObject;
 
import javax.swing.Box;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTree;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.DefaultTreeCellEditor;
import javax.swing.tree.DefaultTreeCellRenderer;
import javax.swing.tree.DefaultTreeModel;
import javax.swing.tree.MutableTreeNode;
import javax.swing.tree.TreeSelectionModel;
 
public class TreeBasic extends JPanel {
  AnilpTreeCellRenderer atcr;
  AnilpTreeCellEditor atce;
  DefaultTreeModel treeModel;
  JTree tree;
  
  public TreeBasic(){
  super(new BorderLayout());
treeModel = new DefaultTreeModel(null);
tree = new JTree(treeModel);
    tree.setEditable(true);
tree.getSelectionModel().setSelectionMode(
TreeSelectionModel.SINGLE_TREE_SELECTION);
tree.setShowsRootHandles(true);
 
    tree.setCellRenderer(atcr = new AnilpTreeCellRenderer(this));
    tree.setCellEditor(atce = new AnilpTreeCellEditor(tree, atcr));
JScrollPane scrollPane = new JScrollPane(tree);
add(scrollPane,BorderLayout.CENTER);
 
  }
 void populate() {
 DefaultMutableTreeNode r = new DefaultMutableTreeNode("Root");
 setRootNode(r);
 
 DefaultMutableTreeNode a = new DefaultMutableTreeNode("Apple");
 treeModel.insertNodeInto(a, r, r.getChildCount());
 
 DefaultMutableTreeNode m = new DefaultMutableTreeNode("Mango");
 treeModel.insertNodeInto(m, r, r.getChildCount());
 
 DefaultMutableTreeNode g = new DefaultMutableTreeNode("Guava");
 treeModel.insertNodeInto(g, r, r.getChildCount());
 
 }
 
 void promote(DefaultMutableTreeNode node) {
 DefaultMutableTreeNode parent = (DefaultMutableTreeNode) node.getParent();
if (parent != null) {
int insIndex = parent.getIndex(node.getPreviousSibling());
treeModel.removeNodeFromParent(node);
treeModel.insertNodeInto(node, (MutableTreeNode) parent, insIndex);
}
 }
public void setRootNode(DefaultMutableTreeNode node) {
treeModel.setRoot(node);
treeModel.reload();
}
 
  public static void main(String[] args){
  TreeBasic tb = new TreeBasic();
    JFrame frame = new JFrame("TreeBasic");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setContentPane(tb);
    frame.setSize(800, 600);
    frame.pack();
    frame.setVisible(true);
    tb.populate();
  }
}
 
class AnilpTreeCellRenderer extends DefaultTreeCellRenderer{
 TreeBasic panel;
 DefaultMutableTreeNode currentNode;
 
  public AnilpTreeCellRenderer(TreeBasic panel) {
super();
this.panel = panel;
}
 
public Component getTreeCellRendererComponent
   (JTree tree, Object value, boolean selected, boolean expanded,
   boolean leaf, int row, boolean hasFocus){
currentNode = (DefaultMutableTreeNode)value;
    Box b = Box.createVerticalBox();
    JTextArea a = new JTextArea(value.toString());
    JButton b1 = new JButton();
    if( (((DefaultMutableTreeNode)value).getUserObject()).equals("Root"))
    b1.setText("Favourites In Order");
    else
    b1.setText("Click to Promote!");
    
    b1.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
panel.promote(currentNode);
}    
    });
    a.setEditable(true);
    b.add(a);
    b.add(b1);
    return b;
  }
}
 
class AnilpTreeCellEditor extends DefaultTreeCellEditor{
  DefaultTreeCellRenderer rend;
 
  public AnilpTreeCellEditor(JTree tree, DefaultTreeCellRenderer r){
    super(tree, r);
    rend = r;
  }
 
  public Component getTreeCellEditorComponent(JTree tree, Object value,
   boolean isSelected, boolean expanded, boolean leaf, int row){
    return rend.getTreeCellRendererComponent(tree, value, isSelected, expanded,
     leaf, row, true);
  }
 
  public boolean isCellEditable(EventObject event){
    return true;
  }
}

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at javax.swing.plaf.basic.BasicTreeUI.completeEditing(Unknown Source)
at javax.swing.plaf.basic.BasicTreeUI.completeEditing(Unknown Source)
at javax.swing.plaf.basic.BasicTreeUI$Handler.valueChanged(Unknown Source)
at javax.swing.tree.DefaultTreeSelectionModel.fireValueChanged(Unknown Source)
at javax.swing.tree.DefaultTreeSelectionModel.notifyPathChange(Unknown Source)
at javax.swing.tree.DefaultTreeSelectionModel.removeSelectionPaths(Unknown Source)
at javax.swing.JTree.removeDescendantSelectedPaths(Unknown Source)
at javax.swing.JTree.removeDescendantSelectedPaths(Unknown Source)
at javax.swing.JTree$TreeModelHandler.treeNodesRemoved(Unknown Source)
at javax.swing.tree.DefaultTreeModel.fireTreeNodesRemoved(Unknown Source)
at javax.swing.tree.DefaultTreeModel.nodesWereRemoved(Unknown Source)
at javax.swing.tree.DefaultTreeModel.removeNodeFromParent(Unknown Source)
at TreeBasic.promote(TreeBasic.java:62)

[Anil Philip]

It is fixed!

 void promote(DefaultMutableTreeNode node) {
 DefaultMutableTreeNode parent = (DefaultMutableTreeNode) node.getParent();
if (parent != null) {
int insIndex = parent.getIndex(node.getPreviousSibling());
tree.setSelectionPath(null);
treeModel.removeNodeFromParent(node);
treeModel.insertNodeInto(node, (MutableTreeNode) parent, insIndex);
}
 }

I had to simply setSelectionPath to null. Anand, God bless you, I dont know if that's what you meant, but that fixed it.