Transparent circle with border

use this it will work

<?xml version="1.0" encoding="utf-8"?>  
     <shape xmlns:android="http://schemas.android.com/apk/res/android"                                                                                                                                                     
   android:shape="oval" >

<gradient
    android:centerX=".6"
    android:centerY=".40"
    android:endColor="@android:color/transparent"
    android:gradientRadius="20"
    android:startColor="@android:color/transparent"
    android:type="radial" />

<stroke
    android:width="1dp"
    android:color="#FFFFFF" />

<size
    android:height="100dp"
    android:width="100dp" />

</shape>

The stroke effect can be achieved drawing a transparent oval with the stroke of a required color (#000 in the example):

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="oval">
    <solid android:color="@android:color/transparent" />
    <stroke
        android:width="1dp"
        android:color="#000" />
    <size
        android:width="40dp"
        android:height="40dp" />
</shape>

Hollow

<?xml version="1.0" encoding="utf-8"?>
    <shape xmlns:android="http://schemas.android.com/apk/res/android"
        android:shape="oval">
        <stroke
            android:width="1dp"
            android:color="@color/indicator_unselected" />
    </shape>

Full

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="oval">
    <corners android:radius="100dp" />
    <solid android:color="@android:color/white" />
</shape>

Try something like this

<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/transparent" />

    <stroke
        android:width="2dp"
        android:color="@android:color/darker_gray" />
</shape>

Update: made android:thicknessRatio="2" to give full circle (using Nexus 5 - Lollipop)