Question

I have been working with Objective-C for a month approximately but regretfully I’m still a complete dummy in memory management so I need your advice. I pass an array from one file to the other like this

         BidView *bidView = [[[BidView alloc] init] autorelease];
         NSLog(@"%i",[bidView.seatsForTableCreated retainCount]);
         bidView.seatsForTableCreated = [NSArray arrayWithArray:seats];
         NSLog(@"%i",[bidView.seatsForTableCreated retainCount]);
         [self.navigationController pushViewController:bidView animated:YES];  `

NSLog tells me that retain count of seatsForTableCreated has raised from zero to two. Then, when I quit the BidView screen (without doing anything with seatsForTableCreated array) I’ m doing the following:

NSLog(@"%i",[seatsForTableCreated retainCount]);
[seatsForTableCreated release];
NSLog(@"%i",[seatsForTableCreated retainCount]);

it’s quite unclear for me. Now NSLog tells me (both times) that retain count is 1. Then I repeat this procedure (running the same application I mean) and each time things are the same:0-2-1-1. So my questions are:
1)Why 0 to 2? Why retain count increases to 2 not to 1?
2)why then it drops to 1 without being impacted in any way?
3)Why it still remains 1 after i’ve released it?
4)How would you manage the memory in such a case?
Great thanks in advance

Answer 1

My advice assumes you are using Xcode 4+ and you are not using ARC,

command+shift+B will analyse your memory management (and dead stores and such). I think you got it right. Don’t worry about the retain counts so much until you get a complaint from Analyze or find leaks with Instruments. I am not sure how reliable retain counts are. I have seen comments on SO saying not to rely on them.

You are following the rules well
New, Alloc, Copy, Retain –> You will need to release this object when you are done with it.

I am also assuming in BidView.h your property is declared as
@property(nonatomic, retain) NSArray * seatsForTableCreated;

So releasing that in the dealloc method in BidView.m is good memory management

EDIT
It works when even though you don’t allocate seats for table created because.
self.seatsForTableCreated = ... will retain whatever object you are setting there.
So if you have a property with (retain) in the declaration, you can consider

self.property = object;

as setting property and retaining it. The properties were added to objective-C to reduce similar code being in every class.

A property in .h

@property (nonatomic,retain) NSObject * property; // don't name your properties property..

Compiler will create 2 methods for you automatically when you @synthesize in the .m

-(void)setProperty:(NSObject*)newP
{
    [newP retain];  // retains the new object so it sticks around for line 3
    [property release]; // releases previous property
    property = newP; // set the property to the object retained in line 1
    // property is now same as newP and you are responsible for releasing it
    // -(void) dealloc   is where you should release it
}

// Note, the compiler may not create the exact same code as above when creating the //setProperty method. If it does, it could be subject to change.

-(NSObject*)property
{
    return property;
}

I tried to figure out why Analyze isn’t catching the issue when you don’t release your property, but haven’t. That is confusing and I want to explore it further.