monotouch - How to draw a linear gradient along an arc in Xamarin iOS -

monotouch - How to draw a linear gradient along an arc in Xamarin iOS -

i'm trying create colour selector tool, similar colour wheel in shape of horse shoe.

i need draw linear gradient follows arc. this

the problem is

a) how create gradient follow curve, instead of going in 1 direction, and

b) how fill stroke of arc , not area enclosed arc

i've managed on android have far failed working in ios, advice appreciated.

ios monotouch xamarin