Here is a simple MonoTouch app that demonstrates how to use Quartz2D
to draw custom progress bars. You can download the MonoDevelop project
here.
This app shows how to draw a simple two color progress bar using
alpha transparency and a simple two color gradient progress bar. There
are sliders that let you control the colors, transparency level, and
progress percentage. The code uses the CGBitmapContext class to create
an image and loads it into UIImageView.
Read Rubin's article with sample code here...