How to convert pcm data to wav file in Objective-c?

I'm now developing an iphone app and have been stuck by the audio stuff. In the app I will get raw data (NSData in PCM) every 256ms. All the raw pcm data should be added together and saved to a .wav file in Document folder. After all the data received, I could use MediaPlayer to play the wav file accordingly.

I made some research and found that a wav header should be added. But how can I do that? Any example code for adding wav file header in objective-c? or any tutorial?