The FragmentPagerAdapter already caches the Fragments for you. Each fragment is assigned a tag, and then the FragmentPagerAdapter tries to call findFragmentByTag. It only calls getItem if the result from findFragmentByTag is null. So you shouldn’t have to cache the fragments yourself.
UPDATE There are many changes done into support library since this question was answered. Good thing is, it is very well documented also. So you must read Support Library Documentation for more details and more available support library. Starting with Support Library release 26.0.0 (July 2017), the minimum supported API level across most support libraries … Read more
LATEST UPDATE – Jun/2019 Support Library has changed a bit since the original answer. Now, even the Android plugin for Gradle is able to automatically generate the PNG at build time. So, below are two new approaches that should work these days. You can find more info here: PNG Generation Gradle can automatically create PNG … Read more