JDialog - Refresh dynamically added nodes in JTree

Question

I have a problem with JTree nodes visibility I use for my JDialog. When I want to add new node to the model the Jtree is not refreshed.

Strange is the nodes are updating just as they should if I set setRootVisible(true).

Here is the code. Thanks in advance

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JDialog;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTree;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.DefaultTreeModel;

public class TestClass {

JTree tree;
DefaultTreeModel dm;
JDialog dialog;

public TestClass(){
    JFrame frame = new JFrame("title");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);

    JPanel showPane = new JPanel();
    showPane.setLayout(new BorderLayout()); 

    dm = new DefaultTreeModel(new DefaultMutableTreeNode("root"));
    tree = new JTree(dm);
    tree.setRootVisible(false);

    JButton button = new JButton("add node");
    button.addActionListener(new ActionListener(){

        public void actionPerformed(ActionEvent arg0) {
            DefaultMutableTreeNode root = (DefaultMutableTreeNode) tree.getModel().getRoot();           
            dm.insertNodeInto(new DefaultMutableTreeNode("Node " + (root.getChildCount() + 1)), root, root.getChildCount());

            int c = root.getChildCount();
            System.out.println("child count: " + c);

            for(int i=0; i<c; i++){
                DefaultMutableTreeNode node = (DefaultMutableTreeNode) root.getChildAt(i);
                System.out.println("has node:" + node.getUserObject().toString());
            }
        }

    });

    showPane.add(tree, BorderLayout.CENTER);
    showPane.add(button, BorderLayout.PAGE_END);

    JComponent[] inputComponents = new JComponent[] {showPane};

    Object[] opButtons = {"OK"};

    JOptionPane optPane = new JOptionPane(inputComponents       
            , JOptionPane.PLAIN_MESSAGE             
            , JOptionPane.CLOSED_OPTION             
            , null                                      
            , opButtons                             
            , opButtons[0]);                            

    optPane.setPreferredSize(new Dimension(400 ,250));

    dialog = optPane.createDialog(null, "Create new Application Node");
    dialog.setLocationRelativeTo(frame);
    dialog.setVisible(true);

    if(optPane.getValue() != null){
        System.exit(0);
    }

}

public static void main(String arg[]){
    TestClass myClass = new TestClass();
}

}

Answer 1

Make sure to expand the path from the parent of the new node to the root each time you add a new child node:

DefaultMutableTreeNode newChild = new DefaultMutableTreeNode("Node " + (root.getChildCount() + 1));
dm.insertNodeInto(newChild, root, root.getChildCount());
tree.expandPath(new TreePath(dm.getPathToRoot(newChild.getParent())));

Answer 2

Please also check another solution:

   DefaultTreeModel model = (DefaultTreeModel) (tree.getModel()); 
   model.reload(); 

API says:

invoke reload method if you've modified the TreeNodes upon which this model depends. The model will notify all of its listeners that the model has changed.

For a quick verification try the following:

public void actionPerformed(ActionEvent arg0) {
   DefaultMutableTreeNode root = (DefaultMutableTreeNode) tree.getModel().getRoot();
   dm.insertNodeInto(new DefaultMutableTreeNode("Node " + (root.getChildCount() + 1)), root, root.getChildCount());

   int c = root.getChildCount();
   System.out.println("child count: " + c);

   DefaultTreeModel model = (DefaultTreeModel) (tree.getModel()); // !!!
   model.reload();   // !!!

   for (int i = 0; i < c; i++) {
       DefaultMutableTreeNode node = (DefaultMutableTreeNode) root.getChildAt(i);
       System.out.println("has node:" + node.getUserObject().toString());
   }
}

Please see the following answer for more details:

• Jtree not shown on adding a node!

Answer 3

The answer by @JBNizet is correct, to summarize:

• inserting a node has no automatic effect on the expansion state of the parent
• so to make sure that the newly inserted child is visible, its parent must be expanded

To throw in a bit of alternative api to make the child visible:

dm.makeVisible(new TreePath(newChild.getPath());

Regarding a comment by @Geoff Reedy (bolding by me):

Normally the root node of a JTree is expanded, but when the tree is created, the root node does not have any children so it cannot be expanded

the cannot is not so strict: whether or not it can be expanded (even with zero children) depends actually on the implementation of the model's isLeaf. Arguably, the root never is a leaf (even without children) because its essence is to not be :-) Can be achieved with

final DefaultTreeModel model = new DefaultTreeModel(root) {

    @Override
    public boolean isLeaf(Object node) {
        if (isRoot(node)) {
            return false;
        }
        return super.isLeaf(node);
    }

    private boolean isRoot(Object node) {
        return node != null && node == getRoot();
    }

};

with such an implementation, the root is always expanded (root visible or not) and newly inserted direct children will show up without making them explicitly visible.