JTree not updating

[pavan in]

I have a jtree which is constructed initially. On some user action, the jtree has to be recreated. But, even though the jtree is re-created, it does not update on the panel. I am putting the jtree inside a scroll pane and then into the panel.
I am first making jtree and the rootnode object null and initializing it again (for re-creating).
Why is the jtree not getting updated? I prinited the jtree and it has the latest values, but still shows the old values on the panel (screen).

[Nathan Pruett]

you'll need to call fireTreeNodesChanged() or fireTreeStructureChanged() in DefaultTreeModel.

[pavan in]

Thanks Nate.
I used scrollpane.getViewport().setView(jtree) method to update the tree.
After setting the view port, the tree does not scroll to the selected node. It scrolls to the top of the tree. Why is that? I am using setSelectionPath() and scrollPathToVisible() method but it does not scroll to selected node.

[Nathan Pruett]

Take a look at the following code... It generates a tree model randomly... generate a new model a few times and you will see the last node is always selected and is always scrolled to visible. It should give you some pointers on what to do...

import java.awt.BorderLayout;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
 
import javax.swing.*;
import javax.swing.tree.*;
 
public class JTreeTest extends JFrame {
    
    private JTree tree;
    private JScrollPane scroll;
    private JButton redo;
    
    public JTreeTest() {
        super( "JTree Test" );
        tree = new JTree( new RandomTreeModel() );
        tree.setScrollsOnExpand( true );
        scroll = new JScrollPane( tree );
        getContentPane().add( scroll );
        JPanel buttons = new JPanel();
        redo = new JButton( "Re-Generate Tree" );
        redo.addActionListener( new ActionListener() {
            public void actionPerformed( ActionEvent evt ) {
                tree.setModel( new RandomTreeModel() );
                DefaultMutableTreeNode root = 
                        (DefaultMutableTreeNode)tree.getModel().getRoot();
                DefaultMutableTreeNode last = root.getLastLeaf();
                TreeNode[] nodes = last.getPath();
                TreePath path = new TreePath( nodes );
                tree.setSelectionPath( path );
                tree.scrollPathToVisible( path );
            }
        } );
        buttons.add( redo );
        getContentPane().add( buttons, BorderLayout.SOUTH );
    }
    
    private class RandomTreeModel extends DefaultTreeModel {
        
        private Random generator = new Random();
        
        public RandomTreeModel() {
            super( new DefaultMutableTreeNode( "RandomTree" ) );
            DefaultMutableTreeNode[] nodes = generateRandomNodes( 5 );
            DefaultMutableTreeNode root = (DefaultMutableTreeNode)getRoot();
            for ( int i = 0; i < nodes.length; i++ ) {
                root.add( nodes[i] );
            }
        }
        
        private DefaultMutableTreeNode[] generateRandomNodes( int depth ) {
            int size = generateRandom( 1, depth );
            DefaultMutableTreeNode[] nodes = new DefaultMutableTreeNode[size];
            if ( size > 0 ) {
                List list = new ArrayList( size );
                for ( int i = 0; i < size; i++ ) {
                    int strSize = generateRandom( 3, 10 );
                    char[] chars = new char[ strSize ];
                    for ( int c = 0; c < strSize; c++ ) {
                        chars[c] = (char)generateRandom( 97, 122 );
                    }
                    String name = new String( chars );
                    DefaultMutableTreeNode node = new DefaultMutableTreeNode( name );
                    if ( depth - 1 > 0 ) {
                        DefaultMutableTreeNode[] child = generateRandomNodes( depth - 1 );
                        for ( int j = 0; j < child.length; j++ ) {
                            node.add( child[j] );
                        }
                    }
                    list.add( node );
                }                
                for ( int i = 0; i < size; i++ ) {
                    nodes[ i ] = (DefaultMutableTreeNode)list.get( i );
                }
            }
            return nodes;
        }
        
        private int generateRandom( int low, int high ) {
            int realHigh = Math.max( low, high );
            int realLow = Math.min( low, high );
            int range = 0;
            for ( int i = realLow; i <= realHigh; i++ ) {
                range++;
            }
            int random = generator.nextInt( range );
            if ( realLow != 0 ) {
                random += realLow;
            }
            return random;
        }
    }
    
    public static void main(String[] args) {
        JFrame f = new JTreeTest();
        f.setDefaultCloseOperation( WindowConstants.EXIT_ON_CLOSE );
        f.setSize( 200, 300 );
        f.show();
    }
}