iPhone declared property

唔明乜野係@property (nonatomic, retain) MyObject* obj?

睇呢度啦：

http://stackoverflow.com/questions/1662772/nsstring-no-assign-retain-or-copy-attribute-is-specified

http://stackoverflow.com/questions/821692/what-does-the-property-nonatomic-mean

Official doc:

http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/ObjectiveC/Articles/ocProperties.html