auto scolling of JEditorPane

Question

I am using a JEditorPane as an editor to write comments in my application. The content type is set "text/plain". When I am writing text in it and the text fills the available space and I go on typing, the text is not moving upward to show the cursor. So I dont know where I am typing and what I am typing since it would be visible.

Could you tell me how to always show the caret by moving the above text upwards?

Instead, it could be better if I can auto-resize the editor as I am typing. The JEditorPane is inside a JPanel, so I have to resize that too. any Ideas?

Aquiver

no i cant use scollpane. at least i cant show scroll bars... :( – Aquiver

Answer 1

You need to put the editor inside a JScrollPane. The ScrollPane will automatically add scrollbars and remove the need to resize the editor.

Neumeyer

no i cant use scollpane. at least i cant show scroll bars... :( – Aquiver

Answer 2

Edited to add full solution

You have to add a JScrollPane first. Then, if you don't want the scrollbars to be visible, but you want the text area to autoscroll, set

scrollPane.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
scrollPane.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_NEVER);

on the scrollpane. This will hide the scrollbars, but provide you with autoscrolling.

Here's how you'd implement auto scrolling with scroll pane, and automatic resize upto a given maximum.

import java.awt.BorderLayout;
import java.awt.Dimension;

import javax.swing.JEditorPane;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.ScrollPaneConstants;
import javax.swing.event.CaretEvent;
import javax.swing.event.CaretListener;


public class SPTest extends JFrame {

    private static final long serialVersionUID = 1L;

    private JEditorPane editor;
    private JScrollPane scrollPane;
    private JPanel topPanel;
    private JLabel labelTop;

    public SPTest() {
        super("Editor test");
        initComponents();
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setVisible(true);
    }

    private void initComponents() {
        editor = new JEditorPane("text/plain", null);
        scrollPane = new JScrollPane(editor);
        topPanel = new JPanel();
        labelTop = new JLabel("main contents here");
        topPanel.add(labelTop);

        setSize(600, 400);
        editor.setMinimumSize(new Dimension(100, 30));
        editor.setPreferredSize(new Dimension(100, 60));
        scrollPane.setPreferredSize(new Dimension(600, 60));
        scrollPane.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
        scrollPane.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_NEVER);
        scrollPane.setMinimumSize(new Dimension(100, 30));

        final int MAX_HEIGHT_RSZ = 120;
        editor.addCaretListener(new CaretListener() {

            public void caretUpdate(CaretEvent e) {
                int height = Math.min(editor.getPreferredSize().height, MAX_HEIGHT_RSZ);
                Dimension preferredSize = scrollPane.getPreferredSize();
                preferredSize.height = height;
                scrollPane.setPreferredSize(preferredSize);
                SPTest.this.validate();
            }
        });

        setLayout(new BorderLayout());
        add(topPanel, BorderLayout.NORTH);
        add(scrollPane, BorderLayout.SOUTH);
    }

    public static void main(String[] args) {
        new SPTest();
    }

}

You could resize You can use this JScrollPane instead of the JPanel as the container for the editor.

Prejudge

How about simply doing myJEditorPane.setCaretPosition(myJEditorPane.getDocument().getLength()); every time the text is updated? – Sweepback