Question

I’m trying to add line numbers to a JTextArea and am having some difficulties. The line numbers appear, but they do not scroll properly.

I have a linked-list of a custom class that stores a line of data (log message) and a line number associated with it as well as visibility on whether it should be shown in the text area or not. So what I did was create two JTextAreas… one to store the logs, and the other to store the line numbers.

The layout works and the line numbers populate correctly with the logs. The problem is when I try to scroll up or down. The logs adjust properly as you scroll, but the line numbers do not. Nothing shows beyond the initial 28 line numbers that are shown initially. The space is just blank.

My code is below:

public class CustomLineNumbers extends JFrame implements ActionListener
{    
    ...
    private JTextArea logField;
    private JTextArea lineField;

    private List<Log> logs;

    public CustomLineNumbers() 
    {       
        ...
        logs = new ArrayList<Log>();

        logField = new JTextArea(28, 68);
        logField.setMargin(new Insets(0, 5, 0, 0));
        logField.setEditable(false);
        logField.setLineWrap(true);
        logField.setWrapStyleWord(true);

        lineField = new JTextArea();
        lineField.setPreferredSize(new Dimension(25, 0));
        lineField.setBackground(this.getForeground());
        lineField.setBorder(OUTER);
        lineField.setEditable(false);

        initLogs();
        updateLogView();
        updateLineView();

        JScrollPane scrollPane = new JScrollPane();
        scrollPane.getViewport().add(logField);
        scrollPane.setRowHeaderView(lineField);
        scrollPane.setVertical...Policy(JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED);

        ...
    }

    private void initLogs()
    {
        // inits the data in the list
    }

    public void updateLogView()
    {
        logField.setText("");   // reset log field to nothing

        for (int i = 0; i < logs.size(); i++)
        {
            // Append only if the line is visible
            if (logs.get(i).getVisibility())
            {
                // if this isn't the first line, 
                // add a line break before appending
                if (i > 0)
                    logField.append("\n");  

                logField.append(logs.get(i).getLine());
            }
        }       
    }

    public void updateLineView()
    {
        lineField.setText("");  // reset log field to nothing

        for (int i = 0; i < logs.size(); i++)
        {
            // Append only if the line is visible
            if (logs.get(i).getVisibility())
            {
                // if this isn't the first line, 
                // add a line break before appending
                if (i > 0)
                    lineField.append("\n"); 

                lineField.append("" + logs.get(i).getLineNumber());
            }
        }       
    }

    ...

    /***** Main Execution *****/
    public static void main(String[] args) { ... }
}

Any ideas?

Thanks,

Answer 1

Have you tried putting both text fields in the viewPort? Maybe on a panel that gives the line numbers a fraction of the available width?