Android: is there a way to apply a right-margin span within an edittext?

Question

I'm looking for something similar to LeadingMarginSpan, but capable of applying both left- and right- margins to the text, as opposed to just a left margin.

What I'm trying to do is have the option of making some paragraphs narrower than others within the same edittext, so it might looks something like this:

blah blah blah blah blah blah blah blah
blah blah blah blah blah blah blah blah
blah blah

     blah blah blah blah blah blah
     blah blah blah blah blah blah
     blah blah blah blah blah blah
     blah

blah blah blah blah blah blah blah blah
blah blah blah blah blah blah blah blah
blah blah blah blah blah

As far as I know there are no pre-defined spans that do this, and I don't know how to go about creating a new span from scratch that could do it. Any help would be greatly appreciated!

Answer 1

You can't set right padding/margin with span. But you can cheat with MetricAffectingSpan. It has two methods: updateMeasureState (called when measuring text) and updateDrawState (called when drawing text).

So, if you increase textScaleX at measuring, android will make shorter lines. If you don't increase textScaleX when drawing, android will not scale lines when drawing. As a result, you'll get shorter lines. That will look like right padding.

It's not perfect: you can't set right padding in pixels, but you will have some padding on right.

Here is 5% right padding example.

public class RoughtRightPaddingSpan extends MetricAffectingSpan {

    @Override
    public void updateMeasureState(TextPaint p) {
        p.setTextScaleX(1.05f);
    }

    @Override
    public void updateDrawState(TextPaint tp) {
    }
}

Answer 2

As far as I know there are no pre-defined spans that do this

AFAIK, you are correct.

and I don't know how to go about creating a new span from scratch that could do it.

Well, support for LeadingMarginSpan is baked into Layout and StaticLayout, so simply creating a TrailingMarginSpan will be insufficient. You would have to create your own custom subclasses of Layout and StaticLayout, overriding and cloning their very complicated draw() methods, and pour in your TrailingMarginSupport.

In short, this will be painful.

If you happen to be making your own firmware, of course, this becomes much simpler... :-)