JTextPane Dynamic Indent !!! Situation

Question

I try to update left indent in the Jtextpane dynamically. But i cant ! Here is what i tried !

DefaultStyledDocument document = (DefaultStyledDocument) textpane.getDocument();
Element element = document.getCharacterElement(start);
AttributeSet attribs = element.getAttributes();
attribs.containsAttribute(StyleConstants.LeftIndent, 20);
document.setCharacterAttributes(start, length, attribs, true);

Answer 1

Here is how you can add an Action to a JButton to indent a paragraph of text:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.text.*;

public class TextPaneIndent extends JPanel
{
    public TextPaneIndent()
    {
        setLayout( new BorderLayout() );

        JTextPane textPane = new JTextPane();
        textPane.setText("one\ntwo\nthree\nfour");
        textPane.setPreferredSize( new Dimension(200, 220) );
        JScrollPane scrollPane = new JScrollPane( textPane );
        scrollPane.setPreferredSize( new Dimension( 200, 200 ) );
        add( scrollPane );

        //  Create a Button panel

        JPanel buttons = new JPanel();
        add(buttons, BorderLayout.PAGE_END);

        //  Add Indent button

        JButton indent = new JButton( new LeftIndentAction("Indent", 10) );
        add( indent );

        //  Add Outdent button

        JButton outdent = new JButton( new LeftIndentAction("Outdent", -10) );
        add( outdent );
    }

    class LeftIndentAction extends StyledEditorKit.StyledTextAction
    {
        private float value;

        public LeftIndentAction(String name, float value)
        {
            super(name);
            this.value = value;
        }

        public void actionPerformed(ActionEvent e)
        {
            JEditorPane editor = getEditor(e);

            if (editor != null)
            {
                StyledDocument doc = getStyledDocument( editor );
                int offset = editor.getCaretPosition();
                Element paragraph = doc.getParagraphElement( offset );
                AttributeSet as = paragraph.getAttributes();
                float indent = StyleConstants.getLeftIndent( as );
                indent += value;

                MutableAttributeSet attr = new SimpleAttributeSet();
                StyleConstants.setLeftIndent(attr, indent);
                setParagraphAttributes(editor, attr, false);
            }
        }
    }

    public static void main(String[] args)
    {
        TextPaneIndent frame = new TextPaneIndent();
        frame.setDefaultCloseOperation( EXIT_ON_CLOSE );
        frame.pack();
        frame.setVisible(true);
    }

    private static void createAndShowGUI()
    {
        JFrame frame = new JFrame("SSCCE");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(new TextPaneIndent());
        frame.pack();
        frame.setLocationByPlatform( true );
        frame.setVisible( true );
    }

    public static void main(String[] args)
    {
        EventQueue.invokeLater( () -> createAndShowGUI() );
    }
}