public override bool BeginTracking(UITouch uitouch, UIEvent uievent)
        {
            previousTouchPoint = uitouch.LocationInView(this);
            if (lowerKnobLayer.Frame.Contains(previousTouchPoint))
            {
                lowerKnobLayer.Highlight = true;
                lowerKnobLayer.SetNeedsDisplay();
            }
            else if (upperKnobLayer.Frame.Contains(previousTouchPoint))
            {
                upperKnobLayer.Highlight = true;
                upperKnobLayer.SetNeedsDisplay();
            }

            return(lowerKnobLayer.Highlight || upperKnobLayer.Highlight);
        }
 private void SetKnobLayer(nfloat centerPosition, CERangeSliderKnobLayer layer)
 {
     layer.Frame         = new CGRect(centerPosition - knobWidth / 2f, 0, knobWidth, knobWidth);
     layer.ShadowOffset  = new SizeF(0, 3);
     layer.ShadowOpacity = 0.4f;
     layer.ShadowColor   = UIColor.Gray.CGColor;
     layer.SetNeedsDisplay();
 }