Dynamic radial circle in the middle of the screen

Dynamic radial circle in the middle of the screen

Why is it so difficult to make this little thing work? : /
I want to create something like android's lock screen. I have an XML:
<shape xmlns:android="http://schemas.android.com/apk/res/android"
android:shape="oval" >
<stroke
android:width="@dimen/dp_5"
android:color="@color/black" />
<gradient
android:type="radial"
android:startColor="@color/green"
android:endColor="@color/red"
android:gradientRadius="@dimen/dp_50" />
</shape>
This circle is a background of a TextView, so the following happens:
1. wrap_content creates a little circle in the center of the screen
2. fill_parent creates an elipse taking the whole screen, instead of a circle

In addition I would like to change the startColor and endColor
programmatically - Didn't find any documentations\threads which solved
this SIMPLE issue.