是否可以创建一个自定义的、动画的MKAnnotationView?

I'm trying to simulate the user location animation in MapKit (where-by the user's position is represented by a pulsating blue dot). I've created a custom subclass of MKAnnotationView and in the drawRect method I'm attempting to cycle through a set of colors. Here's a simpler implementation of what I'm doing:I'm trying to simulate the user location animat