Customize Frame for only top left and bottom left corner in iOS?

Hi,

I've been trying to customize the frame with only top left and bottom left corner in iOS. I tried below code but its not working:
var rect = new CGRect(0,0,
UIBezierPath mPath = UIBezierPath.FromRoundedRect(this.Layer.Bounds, (UIRectCorner.TopLeft | UIRectCorner.BottomLeft),new SizeF(7,7));
CAShapeLayer maskLayer = new CAShapeLayer();
maskLayer.Frame = this.Layer.Bounds;
maskLayer.BackgroundColor = UIColor.Red.CGColor;
maskLayer.Path = mPath.CGPath;
this.Layer.Mask = maskLayer;

thanks again!!!