res/anim/activity_fade_in.xml

<?xml version="1.0" encoding="utf-8"?>
<alpha xmlns:android="http://schemas.android.com/apk/res/android" 
	android:interpolator="@android:anim/linear_interpolator" 
	android:fromAlpha="0.0" 
	android:toAlpha="1.0" 
	android:duration="500" />