ZoomingTextView (Android)

public class ZoomingTextView extends TextView {

    private static final int DEFAULT_TEXT_SIZE = 18;
    private static final int MINIMAL_TEXT_SIZE = 6, MAXIMAL_TEXT_SIZE = 50;
    private static final float MIN_SCALE = MINIMAL_TEXT_SIZE / (float) DEFAULT_TEXT_SIZE;
    private static final float MAX_SCALE = MAXIMAL_TEXT_SIZE / (float) DEFAULT_TEXT_SIZE;

    private ScaleGestureDetector scaleDetector;
    private float scaleFactor;

    public ZoomingTextView(Context context) {
        super(context);
        init(context);
    }

    public ZoomingTextView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(context);
    }

    public ZoomingTextView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        init(context);
    }

    private void init(Context context) {
        scaleDetector = new ScaleGestureDetector(context, new ScaleListener());
        scaleFactor = 1.0f;
    }


    @Override
    public boolean onTouchEvent(MotionEvent event) {
        scaleDetector.onTouchEvent(event);
        return super.onTouchEvent(event);
    }

    private class ScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener {

        @Override
        public boolean onScale(ScaleGestureDetector detector) {
            scaleFactor *= detector.getScaleFactor();
            scaleFactor = Math.max(MIN_SCALE, Math.min(scaleFactor, MAX_SCALE));

            final int textSize = (int) (scaleFactor * DEFAULT_TEXT_SIZE);
            setTextSize(textSize);

            return true;
        }
    }
}