Question

I am stuck in the middle of memory management stuff. Please help me out in solving my question.

NSMutableArray *array = [[NSMutableArray alloc]init];
Object *obj = [[Object alloc]init];  
[array addObject: obj];  
[obj release];  

Is it necessary to release obj in above code?

Answer 1

The answer to your question is: yes, if you don’t use ARC. If you are writing a new app, you should seriously consider using ARC.

Container objects in Objective-C always balance their retain/release count. In other words, you should always manage memory as if you did not add the object and make sure your own code balances its retain count. Note that this is a convention and is not enforced, but you could always trust the built-in classes to follow this convention. Also, you can perform a static analysis (Cmd+Shift+B in XCode) to detect these problems. It would have pinpointed this in your code above.

The correct code in the case above would be:

NSMutableArray *array = [[NSMutableArray alloc]init];
Object *obj = [[[Object alloc]init]autorelease];
[array addObject: obj];

or

NSMutableArray *array = [[NSMutableArray alloc]init];
Object *obj = [[Object alloc]init];
[array addObject: obj];
[obj release];

since NSMutableArray (and its cousins) will retain the object as long as it is in the collection.