If you want a circle like this
Try using the code below:
<shape xmlns:android="http://schemas.android.com/apk/res/android"
android:innerRadius="0dp"
android:shape="ring"
android:thicknessRatio="2"
android:useLevel="false" >
<solid android:color="@android:color/white" />
<stroke
android:width="1dp"
android:color="@android:color/darker_gray" />
</shape>