Question

I am using a JPanel with some JLabels and JTextFields as editor and renderer in a JTree.

The user can click on any JTextField and modify the text. All works fine.

All I am missing is how I can dynamically resize (grow) the JTextField as the user is typing.

Below a small sample program that illustrates the problem. Click on i.e. “colors” and enter some additional characters. The JTextField keeps its size, which is expected, but I would like it to grow and shrink to accommodate the text.

I tried different layout managers, calculate the preferredSize of the JTextField and the JPanel, call invalidate() and the JPanel and the Tree and so on, without success.

Any ideas?

import java.awt.Component;
import java.util.EventObject;

import javax.swing.AbstractCellEditor;
import javax.swing.BoxLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTree;
import javax.swing.tree.TreeCellEditor;
import javax.swing.tree.TreeCellRenderer;

public class Tree {

    public static void main(final String[] args) {
        new Tree().grow();
    }

    private void grow() {
        final JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        final JTree tree = new JTree();
        tree.setEditable(true);
        tree.setCellRenderer(new SomeTreeCellRenderer());
        tree.setCellEditor(new SomeTreeCellRenderer());

        frame.add(new JScrollPane(tree));

        frame.pack();
        frame.setSize(400, 300);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    private class SomeTreeCellRenderer extends AbstractCellEditor implements 
            TreeCellRenderer, TreeCellEditor {

        @Override
        public Object getCellEditorValue() {
            return null;
        }

        @Override
        public boolean isCellEditable(final EventObject event) {
            return true;
        }

        @Override
        public Component getTreeCellRendererComponent(
                final JTree tree, final Object value, final boolean selected, final boolean expanded, 
                final boolean leaf, final int row, final boolean hasFocus) {

            final JPanel panel = new JPanel();
            final BoxLayout layout = new BoxLayout(panel, BoxLayout.X_AXIS);
            panel.setLayout(layout);

            panel.add(new JLabel("Some text: "));
            panel.add(new JTextArea(String.valueOf(value)));

            return panel;
        }

        @Override
        public Component getTreeCellEditorComponent(
                final JTree tree, final Object value, final boolean isSelected,
                final boolean expanded, final boolean leaf, final int row) {

            return getTreeCellRendererComponent(tree, value, isSelected, expanded, leaf, row, false);
        }

    }

}

Answer 1

What’s happening is that the container owning your panel doesn’t have a layout manager assigned to it – so the panel is not resizing when the text area is resizing. A simple fix to this would be to set the size of the panel whenever your text area resizes. So instead of directly doing this:

        panel.add(new JTextArea(String.valueOf(value)));

You can do this:

        JTextArea ta = new JTextArea(String.valueOf(value));
        ta.addComponentListener(new ComponentListener() {

            @Override
            public void componentResized(ComponentEvent e) {
                panel.setSize(panel.getPreferredSize());
            }

            @Override
            public void componentShown(ComponentEvent e) {}

            @Override
            public void componentMoved(ComponentEvent e) {}

            @Override
            public void componentHidden(ComponentEvent e) {}
        });

        panel.add(ta);