Retain/Release, Properties, and ‘self’

Posted by admin on Dec 22, 2008 in iPod / iPhone, Mac OS X |

I think I learned something today about Objective C properties and retain.  It seems that in a method where you reference a property, you need to use the form “self.property_name” if you want the assigned object to be automagically retained.  If you simply say “property_name = some_object” it doesn’t retain some_object!

Witness the source code and the associated results:

Source: Retain Release main.m

Results:

2008-12-22 20:52:18.824 RetainRelease[3623:10b] Before assignment: [a retainCount] = 1
2008-12-22 20:52:18.837 RetainRelease[3623:10b] After assignment: [a retainCount] = 1
2008-12-22 20:52:18.838 RetainRelease[3623:10b] Before assignment: [b retainCount] = 1
2008-12-22 20:52:18.839 RetainRelease[3623:10b] After assignment: [b retainCount] = 2
2008-12-22 20:52:18.842 RetainRelease[3623:10b] Final [oo retainCount] = 2

Seems to me proof that when you’re assigning to them, you should always reference properties on an object by prefixing them with “self“.

Caveat: Inside of the setter method for a property, do NOT use the “self.property” syntax. Otherwise, you end up in a infinite loop. Ask me how I know. :-) This is the best (and only) argument I can see for having a different behavior between the “self.property =” and “property =” usages.

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