Java SWT show Line numbers for StyledText

Question

I was wondering if there is a straightforward way to display line numbers with StyledText text field - even if lines are wrapped. I'm using it in my application and if content gets to big, some line numbers would be nice.

Thank you.

Answer 1

The key is org.eclipse.swt.custom.Bullet. It's basically a symbol (or in our case a number) you can add to the beginning of a line.

//text is your StyledText
text.addLineStyleListener(new LineStyleListener()
{
    public void lineGetStyle(LineStyleEvent e)
    {
        //Set the line number
        e.bulletIndex = text.getLineAtOffset(e.lineOffset);

        //Set the style, 12 pixles wide for each digit
        StyleRange style = new StyleRange();
        style.metrics = new GlyphMetrics(0, 0, Integer.toString(text.getLineCount()+1).length()*12);

        //Create and set the bullet
        e.bullet = new Bullet(ST.BULLET_NUMBER,style);
    }
});

Answer 2

This is my working implementation.

styledText.addLineStyleListener(new LineStyleListener() {
    @Override
    public void lineGetStyle(LineStyleEvent event) {
        // Using ST.BULLET_NUMBER sometimes results in weird alignment.
        //event.bulletIndex = styledText.getLineAtOffset(event.lineOffset);
        StyleRange styleRange = new StyleRange();
        styleRange.foreground = Display.getCurrent().getSystemColor(SWT.COLOR_GRAY);
        int maxLine = styledText.getLineCount();
        int bulletLength = Integer.toString(maxLine).length();
        // Width of number character is half the height in monospaced font, add 1 character width for right padding.
        int bulletWidth = (bulletLength + 1) * styledText.getLineHeight() / 2;
        styleRange.metrics = new GlyphMetrics(0, 0, bulletWidth);
        event.bullet = new Bullet(ST.BULLET_TEXT, styleRange);
        // getLineAtOffset() returns a zero-based line index.
        int bulletLine = styledText.getLineAtOffset(event.lineOffset) + 1;
        event.bullet.text = String.format("%" + bulletLength + "s", bulletLine);
    }
});
styledText.addModifyListener(new ModifyListener() {
    @Override
    public void modifyText(ModifyEvent e) {
        // For line number redrawing.
        styledText.redraw();
    }
});

Note that the possible overhead of syntax highlighting recalculation when calling redraw() is likely to be acceptable, because lineGetStyle() are only called with lines currently on screen.