res/animator/reverse.xml

<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android"
    android:interpolator="@android:anim/linear_interpolator" >

    <rotate
        android:duration="500"
        android:fromDegrees="180"
        android:pivotX="50%"
        android:pivotY="50%"
        android:startOffset="0"
        android:toDegrees="0" />

</set>