@Override
        public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
            if (isRotationEnabled) {
                // Set up the Scroller for a fling
                final RectF circleOval = pieChart.getCircleOval();
                final float centerX = circleOval.centerX();
                final float centerY = circleOval.centerY();
                float scrollTheta = vectorToScalarScroll(velocityX, velocityY, e2.getX() - centerX, e2.getY() -
                        centerY);
                scroller.abortAnimation();
                scroller.fling(0, (int) pieChart.getChartRotation(), 0, (int) scrollTheta / FLING_VELOCITY_DOWNSCALE,
                        0, 0, Integer.MIN_VALUE, Integer.MAX_VALUE);
                return true;
            }

            return false;
        }
Reference to PieChartView to use some methods specific for that kind of chart.
hellocharts-library/src/lecho/lib/hellocharts/gesture/PieChartTouchHandler.java