圆形径向渐变按钮

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

    <item android:state_pressed="true"><shape android:shape="oval" android:useLevel="false">
            <gradient android:angle="90" android:centerX="0.5" android:centerY="0.5" android:endColor="#c6c6c6" android:gradientRadius="100%" android:startColor="#e4e4e4" android:type="radial" android:useLevel="false" />

            <size android:height="20dp" android:width="20dp"></size>

            <stroke android:width="1dp" android:color="#fff" />
        </shape></item>
    <item android:state_pressed="false"><shape android:shape="oval" android:useLevel="false">
            <gradient android:angle="90" android:centerX="0.5" android:centerY="0.5" android:endColor="#c6c6c6" android:gradientRadius="100%" android:startColor="#e4e4e4" android:type="radial" android:useLevel="false" />

            <size android:height="20dp" android:width="20dp"></size>

            <stroke android:width="1dp" android:color="#fff" />
        </shape></item>
      

</selector>