text displaying in a JTextArea

问题:

I'm working on a window that is supposed to represent a chat box of a dialogue between the user and the my program. What I want is that the user messages end up on the right side of the conversation zone and the messages generated by the computer end up on the left side. The conversation zone that I have is a JtextArea with a scrollbar

回答1:

You can use a JTextPane and set "paragraph" attributes as you add text to the text pane to control the right/left alignment.

Here is a simple example that shows how to "center" text as it is inserted. The concept is the same for right/left alignment.

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

public class TextPaneAttributes extends JPanel
{

    public TextPaneAttributes()
    {
        setLayout( new BorderLayout() );

        JTextPane textPane = new JTextPane();
        textPane.setText( "one\ntwo\nthree\nfour\nfive\nsix\nseven\neight" );

//      DefaultHighlighter highlighter =  (DefaultHighlighter)textPane.getHighlighter();
//      highlighter.setDrawsLayeredHighlights(false);

        //  Define some character and paragraph attributes

        SimpleAttributeSet keyWord = new SimpleAttributeSet();
        StyleConstants.setBold(keyWord, true);

        SimpleAttributeSet green = new SimpleAttributeSet();
        StyleConstants.setForeground(green, Color.GREEN);

        SimpleAttributeSet center = new SimpleAttributeSet();
        StyleConstants.setAlignment(center, StyleConstants.ALIGN_CENTER);

        SimpleAttributeSet left = new SimpleAttributeSet();
        StyleConstants.setAlignment(left, StyleConstants.ALIGN_LEFT);

        //  Change attributes on some existing text

        StyledDocument doc = textPane.getStyledDocument();
        doc.setCharacterAttributes(0, 3, keyWord, false);
        doc.setCharacterAttributes(8, 5, green, true);
        doc.setParagraphAttributes(20, 1 , center, false);

        //  Add some text with attributes

        try
        {
            doc.insertString(doc.getLength(), "\nNormal text", null);
            doc.insertString(doc.getLength(), "\nGreen text centered", green);
            doc.setParagraphAttributes(doc.getLength(), 1 , center, false);
            doc.insertString(doc.getLength(), "\nKeyword text", keyWord);
            doc.setParagraphAttributes(doc.getLength(), 1 , left, false);

            //  Newly typed text at the end of the document will inherit the
            //  "keyword" attributes unless we remove the attributes

            textPane.setCaretPosition(doc.getLength());
            textPane.getInputAttributes().removeAttributes(keyWord);
        }
        catch(Exception e) {}

        //  Add text pane to frame

        JScrollPane scrollPane = new JScrollPane( textPane );
        scrollPane.setPreferredSize( new Dimension( 200, 250 ) );
        add( scrollPane );

        //  Create a Button panel

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

        //  Add a Bold button

        JButton bold = new JButton( new StyledEditorKit.BoldAction() );
        buttons.add( bold );

        //  Add Right Alignment button

        JButton right = new JButton( new StyledEditorKit.AlignmentAction("Align Right", StyleConstants.ALIGN_RIGHT) );
        buttons.add( right );
    }

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

    public static void main(String[] args)
    {
        EventQueue.invokeLater( () -> createAndShowGUI() );
/*
        EventQueue.invokeLater(new Runnable()
        {
            public void run()
            {
                createAndShowGUI();
            }
        });
*/
    }
}