To help other developers learn Android, Bill Lahti has written blog articles about Android. See http://blahti.wordpress.com for complete notes and explanations for all of the attached sample applications.
Most of these tutorial were done prior to 2017. The zip files are for use with Eclipse.
Android Example of a Zoomable Game Board - an example application with a game board that can be panned and zoomed.
How to Implement In-App Billing in Android - a modified version of a sample app from Google for in-app purchases.
Rotate and Scale Bitmap Example - a simple demo app that shows how to display bitmaps on a canvas with rotation and scaling.
Store Item Fragment - a fragment that displays an item for sale in a virtual store.
Tridroid - Switch Fragment Demo - a fragment that implements a simple switch
Two Progress Bars for Android - an example that shows how to build two simple progress bars for your Android app.
Drag-Drop for Android GridView (V4) - a demo app that shows how to support drag-drop operations in a GridView.
Fragments Example V4 - a simple example that shows how to support Fragments in an application for all API levels from Android 2.3.3 (API 10) to Android 4.2 and up (API 17+)