I was wondering if there is a class diagram for the Android API on the Internet? I think this will help you learn and visualize the system in your head.
Here is an excellent classified list of classes in the Android API in PDF and Visio formats: from Troodon Software: http://gyurigrell.com/2011/1/17/great-android-class-diagram-poster p>
While this is not a class diagram, it is still very useful. Maybe I will start creating the right hierarchical class diagram at some point ...
This chart helped me: http://www.adakoda.com/adakoda/2010/01/20/ASPH_AW_REV1.pdf
It may be a little old, but here you can find a poster for Android:
http://gyurigrell.com/2011/01/great-android-class-diagram-poster/
Could you check the source code? Any decent IDE can create a class diagram from source code. This way you will have both code and basic design.
Of course, Android is available in Git.https://android.googlesource.com