How to make a circle drawable?

How to make a circle drawable?

ref:http://stackoverflow.com/questions/14209725/how-can-i-draw-circle-through-xml-drawable-android

need custom wediget?ref:https://developer.android.com/training/custom-views/index.html

customview ref

:http://www.intertech.com/Blog/android-custom-view-tutorial-part-2-custom-attributes-drawing-and-measuring/