I looked over SensorManager and was still unsure, how do I detect if the phone is looking at true north (or any other direction for that matter).
If you are just looking for a sample, the publishers of Professional Android 2 Application Development have all their example code available for download and there is a compass application in chapter 14.
来源：https://stackoverflow.com/questions/2808811/determining-north-using-the-android-phone