Android TextView edit

Make RelativeSizeSpan align to top

In order to make a RelativeSizeSpan align to the top, a custom class can be derived from the class SuperscriptSpan. In the following example, the derived class is named TopAlignSuperscriptSpan:

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 );
    }
}

Reference screenshot:

 

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