Android magnitude calibration

I met a magnitude calibration problem when I was developing a project using magnitude. I have used two ways to calibrate the magnitude sensor.

I implemented a small sensor reading program and rotated my Android phone in eight shape to make the magnetometer get back on track.
I opened Google map and then rotated my Android phone in eight shape.
The solution one seems not to be helpful while the solution two is effective. But what I really want is a calibration mechanism for magnitude inside my application. How can I implement this kind of calibration in my app?