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  1. #1

    Member Since
    Feb 21, 2011
    Macbook Air 11", 64 GB, Intel core i5, 1.6 GHz, OSX Lion 10.7
    What does nonatomic and retain do in Objective-C?
    Hello every1

    In objective-c when we apply synthesize accessor method or when we write property, we also use 2 terms, they are: nonatomic and retain. the syntax is given below:

    @property(nonatomic, retain)

    I would like to know what exactly nonatomic and retain do.
    Please guide
    reply soon..


  2. #2

    xstep's Avatar
    Member Since
    Jun 25, 2005
    On the road
    2011 MBP, i7, 16GB RAM, MBP 2.16Ghz Core Duo, 2GB ram, Dual 867Mhz MDD, 1.75GB ram, ATI 9800 Pro vid
    Both are discussed here in The Objective-C Programming Language. Search that document for those two words.

    In short...

    The nonatomic directive means no locking of the variable is done during access. This speeds up access. In a multithreading scenario that could be a bad thing.

    The retain directive means that upon assignment, the object will be retained. If you override the properties setter method, I believe you are then responsible for the retain.
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