How to make RelativeSizeSpan align to top

However I did in this way:

activity_main.xml:

<TextView
    android:id="@+id/txtView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginTop="50dp"
    android:textSize="26sp" />

MainActivity.java:

TextView txtView = (TextView) findViewById(R.id.txtView);

SpannableString spannableString = new SpannableString("RM123.456");
spannableString.setSpan( new TopAlignSuperscriptSpan( (float)0.35 ), 0, 2, Spanned.SPAN_EXCLUSIVE_EXCLUSIVE );
txtView.setText(spannableString);

TopAlignSuperscriptSpan.java:

private class TopAlignSuperscriptSpan extends SuperscriptSpan {
        //divide superscript by this number
        protected int fontScale = 2;

        //shift value, 0 to 1.0
        protected float shiftPercentage = 0;

        //doesn't shift
        TopAlignSuperscriptSpan() {}

        //sets the shift percentage
        TopAlignSuperscriptSpan( float shiftPercentage ) {
            if( shiftPercentage > 0.0 && shiftPercentage < 1.0 )
                this.shiftPercentage = shiftPercentage;
        }

        @Override
        public void updateDrawState( TextPaint tp ) {
            //original ascent
            float ascent = tp.ascent();

            //scale down the font
            tp.setTextSize( tp.getTextSize() / fontScale );

            //get the new font ascent
            float newAscent = tp.getFontMetrics().ascent;

            //move baseline to top of old font, then move down size of new font
            //adjust for errors with shift percentage
            tp.baselineShift += ( ascent - ascent * shiftPercentage )
                    - (newAscent - newAscent * shiftPercentage );
        }

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

Hope this will help you.

I had a look at the RelativeSizeSpan and found a rather simple implementation. So you could just implement your own RelativeSizeSpan for your purpose. The only difference here is that it doesn't implement ParcelableSpan, since this is only intended for framework code. AntiRelativeSizeSpan is just a fast hack without much testing of course, but it seems to work fine. It completely relies on Paint.getTextBounds() to find the best value for the baselineShift, but maybe there'd be a better approach.

public class AntiRelativeSizeSpan extends MetricAffectingSpan {
    private final float mProportion;

    public AntiRelativeSizeSpan(float proportion) {
        mProportion = proportion;
    }

    public float getSizeChange() {
        return mProportion;
    }

    @Override
    public void updateDrawState(TextPaint ds) {
        updateAnyState(ds);
    }

    @Override
    public void updateMeasureState(TextPaint ds) {
        updateAnyState(ds);
    }

    private void updateAnyState(TextPaint ds) {
        Rect bounds = new Rect();
        ds.getTextBounds("1A", 0, 2, bounds);
        int shift = bounds.top - bounds.bottom;
        ds.setTextSize(ds.getTextSize() * mProportion);
        ds.getTextBounds("1A", 0, 2, bounds);
        shift += bounds.bottom - bounds.top;
        ds.baselineShift += shift;
    }
}