This project used to be the homework of the Coursera Android course: https://class.coursera.org/android-002/wiki/Module_5

It is here to answer the following questions:

1. How to dynamically register and unregister a BroadcastReceiver?
2. How to add intent filter to a BroadcastReceiver?
3. What is the difference between a normal broadcast and an ordered broadcast? And how to use the getResultData() and getResultCode() of an ordered broadcast?
4. How to take the advantage of a customized Notification?
5. How to use the AsyncTask? How to check whether the main Activity is active?