Perhaps the largest change in Android 3.0 facing Android developers is the introduction of the fragment system. This is an optional layer you can put between your activities and your widgets, designed to help you reconfigure your activities to support screens both large (e.g., tablets) and small (e.g., phones). However, the fragment system also adds an extra layer of complexity, one that will take the Android developer community some time to adjust to. Hence, for the time being, you will find few blog posts or sample apps using fragments because they were introduced so long after Android itself was.
This chapter covers basic uses of fragments, including supporting fragments on pre-Android 3.0 devices.