使用Quartz 2D / Core Graphics完成此绘图的最佳方法是什么？

As the background for one of the views in my app, I'd like to draw a fairly simple rectangular border just inside its frame. This would essentially be a rectangular gradient: a black line around the frame, fading to white about 10-20 pixels in. Unfortunately, as far as I can tell, Core Graphics doesn't provide rectangular gradients (either with As the background for one of the views in my ap