As an Android apps developer, the best case study may be the open source android applications or samples. Below is my memo of open source android applications which I have found in the Internet, hope this will be useful for you.
No.1: Android SDK Samples: The best way to learn how things are done is to look at some code.
To help Android developers get started quickly, the Android SDK includes a variety of sample code and tutorials that illustrate key concepts and techniques of Android application development. The list below provides a summary of the sample applications that are available with the Android SDK:
1. API Demos
A variety of small applications that demonstrate an extensive collection of framework topics.
2. Bluetooth Chat
An application for two-way text messaging over Bluetooth.
An application that demonstrates how to launch the built-in contact picker from within an activity. This sample also uses reflection to ensure that the correct version of the contacts API is used, depending on which API level the application is running under.
4. Contact Manager
An application that demonstrates how to query the system contacts provider using the ContactsContract API, as well as insert contacts into a specific account.
A home screen replacement application.
A game that demonstrates the SONiVOX JET interactive music technology, with JetPlayer.
7. Live Wallpaper
An application that demonstrates how to create a live wallpaper and bundle it in an application that users can install on their devices.
8. Lunar Lander
A classic Lunar Lander game.
9. Multiple Resolutions
A sample application that shows how to use resource directory qualifiers to provide different resources for different screen configurations.
An application for saving notes. Similar (but not identical) to the Notepad tutorial.
Demonstrates how an application can communicate with a cloud-based service and synchronize its data with data stored locally in a content provider. The sample uses two related parts of the Android framework — the account manager and the synchronization manager (through a sync adapter).
12. Searchable Dictionary
A sample application that demonstrates Android’s search framework, including how to provide search suggestions for Quick Search Box.
An implementation of the classic game “Snake.”
14. Soft Keyboard
An example of writing an input method for a software keyboard.
An example of creating interactive widgets for display on the Android home screen.
16. Wiktionary (Simplified)
A simple Android home screen widgets example.