What is the best way to get the android sdk reference offline on my android device? I want to study the Android API on my phone during my frequent and long metro rides (where I cannot connect to the internet). 
What would be the best way to make the documentation available (I would appreciate being able to use a search option and an index) ?
Is copying all the documentation files from my PC to my Android device the best thing to do ? Is there any serious app that could provide this features ?
You can download the documentation of Ice Cream Sandwich (Android 4.0) by the SDK Manager.

SDK manager-->Android 4.0.3 (API15)-->Documentation for Android SDK

It will download all the documentation in &lt;android-sdk&gt;\docs of your PC.