TabStops

[Steve Sinai]

Hi - Does anyone know if there's a way to set TabStop.ALIGN_DECIMAL on a JTextPane as a default, i.e., without creating a TabSet containing lots of TabStops? I have a JTextPane with lots of numbers I'd like to align using tabs.

Thanks,
Steve Sinai

[Brian Cole]

The short answer is no. Nothing is impossible and you could muck around with the Views and ViewFactories and such, but that would be much more work than just using TabStop and TabSet. Why are you reluctant to use those?

[Steve Sinai]

I actually do use TabStops and TabSets now, but I was hoping there was an easy way to set the default behavior to align tabs along a decimal point in a number, rather than creating a bunch of TabStops and a TabSet. My pages are pretty dynamic, and it's hard to know how many TabStops will be needed on a page. Right now I'm just creating an array of 100 TabStops, but it's inevitable that someone's going to come up with a document that needs more than 100.

[Brian Cole]

I've been thinking about this off and on, and I've decided it's actually not all that difficult to customize a View to do this.

import javax.swing.text.*;
 
/**
 * DecimalParagraphView - a simple subclass of ParagraphView that
 * overrides nextTabStop() to make implicit tabs decimal-aligned.
 * <p>
 * To actually use this class, you must convince a ViewFactory
 * to return DecimalParagraphViews instead of ParagraphViews.
 * 
 * @author Brian Cole
 */
public class DecimalParagraphView extends ParagraphView {
 
private static final char[] DECS = { '.', '\t' };

private boolean leftAligned = true;
 
/** @see ParagraphView#ParagraphView(Element) */
public DecimalParagraphView(Element element) {
super(element);
}
 
/** overridden to simulate decimal-aligned tab stops by default */
public float nextTabStop(float x, int tabOffset) {
float base = super.nextTabStop(x, tabOffset);
// return supervalue if not ALIGN_LEFT
if (!leftAligned) return base;
// return supervalue if an explicit TabStop applies
TabSet tabSet = getTabSet();
if (tabSet != null) {
TabStop tab = tabSet.getTabAfter(x+0.01f);
if (tab != null) return base;
}
// find the position of the next decimal point (or next tab, or the end)
int pos = findOffsetToCharactersInString(DECS, 1+tabOffset);
if (pos == -1) pos = getEndOffset();
// compute the delta from the supervalue
float delta = getPartialSize(1+tabOffset, pos);
// check if delta is too big
if (base-delta <= x) return x+10;
// subtract the delta
return base-delta;
}
 
/** overridden to peek at the value and set the 'leftAligned' flag
    (The 'justification' field is in private in the superclass.) */
protected void setJustification(int j) {
leftAligned = (j == StyleConstants.ALIGN_LEFT);
super.setJustification(j);
}
 
}
 

Alas, it is cumbersome to actually use DecimalParagraphView in a JTextPane. I'll post some sample code in a subsequent post.

[Brian Cole]

Originally posted by Brian Cole:
Alas, it is cumbersome to actually use DecimalParagraphView in a JTextPane. I'll post some sample code in a subsequent post.

import javax.swing.*;
import javax.swing.text.*;
 
public class TryIt {
 
public static void main(String[] argv) {
JTextPane tp = new JTextPane();
[B]tp.setEditorKit(new DecimalEditorKit());[/B]
tp.setText("\t1.0\t1.0\t1.0\t1.0\n"
          +"\t200.002\t200.002\t200.002\t200.002\n"
          +"\t.33\t.33\t.33\t.33\n"
          +"\tfoo\tbar\tbaz\tola\n");

JFrame f = new JFrame("Try DecimalParagraphView");
f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
f.setContentPane(new JScrollPane(tp));
f.setSize(400, 300);
f.setVisible(true);
}
 
// **************** begin inner classes ****************
 
/**
 * DecimalViewFactory returns a DecimalParagraphView for paragraph elements.
 * For other elements it delegates to the factory passed to the constructor.
 */
static class DecimalViewFactory implements ViewFactory {
private ViewFactory delegate;
 
public DecimalViewFactory(ViewFactory delegate) {
this.delegate = delegate;
}
 
public View create(Element element) {
if (AbstractDocument.ParagraphElementName.equals(element.getName()))
[B]return new DecimalParagraphView(element);[/B]
return delegate.create(element);
}
}
 
/**
 * DecimalEditorKit is exactly like StyledEditorKit except that its
 * ViewFactory returns DecimalParagraphViews instead of ParagraphViews.
 */
static class DecimalEditorKit extends StyledEditorKit {
private ViewFactory decimalViewFactory = new DecimalViewFactory(super.getViewFactory());

public ViewFactory getViewFactory() {
return decimalViewFactory;
}
}
 
}

[ January 04, 2007: Message edited by: Brian Cole ]