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javaswingjscrollpaneviewportjtree

Set viewport at the end of the JTree on inserting a new node

I have a JTree which is in a JScrollPane. I would like to update the viewport and set it to the end of the JTree upon inserting a new node.

I want to do something similar to this...

   scrollPane = new JScrollPane( textPane ));
   scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);

   DefaultCaret caret = (DefaultCaret) textPane.getCaret();
   caret.setUpdatePolicy(DefaultCaret.ALWAYS_UPDATE);

but with JTree not JTextPane. The JTree class does not have a getCaret() method, so I have checked the JTree API but could not find what I need. Is there an easy way to get this working?

Solution

  • You can get the JViewport of the scroll pane, and use JViewPort#scrollRectToVisible(Rectangle contentRect). Something like

    int y = tree.getPreferredSize().height;
pane.getViewport().scrollRectToVisible(new Rectangle(0, y, 0, 0));

    Here's a full example

    import java.awt.Rectangle;
import javax.swing.*;
import javax.swing.tree.DefaultMutableTreeNode;

public class TestViewPort {
    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable(){
            public void run() {
                DefaultMutableTreeNode root = new DefaultMutableTreeNode("Root");
                for (int i = 0; i < 100; i++) {
                    root.add(new DefaultMutableTreeNode(Integer.toString(i)));
                }
                JTree tree = new JTree(root);
                tree.setVisibleRowCount(10);
                JScrollPane pane = new JScrollPane();
                pane.setViewportView(tree);
                int y = tree.getPreferredSize().height;
                pane.getViewport().scrollRectToVisible(new Rectangle(0, y, 0, 0));
                JOptionPane.showMessageDialog(null, pane);
            }  
        });
    }
}
    • Or simply as AndrewThompson pointed out tree.scrollRectToVisible(new Rectangle(0, y, 0, 0));, as JTree also has this method.

    UPDATE: probably best solution