Circular gradient in android

You can get a circular gradient using android:type="radial":

<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">
    <gradient android:type="radial" android:gradientRadius="250dp"
        android:startColor="#E9E9E9" android:endColor="#D4D4D4" />
</shape>

I always find images helpful when learning a new concept, so this is a supplemental answer.

The %p means a percentage of the parent, that is, a percentage of the narrowest dimension of whatever view we set our drawable on. The images above were generated by changing the gradientRadius in this code

my_gradient_drawable

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">
    <gradient
        android:type="radial"
        android:gradientRadius="10%p"
        android:startColor="#f6ee19"
        android:endColor="#115ede" />
</shape>

Which can be set on a view's background attribute like this

<View
    android:layout_width="200dp"
    android:layout_height="100dp"
    android:background="@drawable/my_gradient_drawable"/>

Center

You can change the center of the radius with

android:centerX="0.2"
android:centerY="0.7"

where the decimals are fractions of the width and height for x and y respectively.

Documentation

Here are some notes from the documentation explaining things a little more.

android:gradientRadius

Radius of the gradient, used only with radial gradient. May be an explicit dimension or a fractional value relative to the shape's minimum dimension.

May be a floating point value, such as "1.2".

May be a dimension value, which is a floating point number appended with a unit such as "14.5sp". Available units are: px (pixels), dp (density-independent pixels), sp (scaled pixels based on preferred font size), in (inches), and mm (millimeters).

May be a fractional value, which is a floating point number appended with either % or %p, such as "14.5%". The % suffix always means a percentage of the base size; the optional %p suffix provides a size relative to some parent container.