NSMutableArray: Memory management while calling methods

Question

In my iOS app, I am using a NSMutableArray, named imageMArray. I have set its getter and setter properties and instantiated it.

In viewDidLoad:

imageMArray=[[NSMutableArray alloc] initWithArray:CategoryImages];
imageMArray=[self shuffleOnlyArray:imageMArray];

In ShuffleOnlyArray Method:

 NSMutableArray *destArray1 = [[NSMutableArray alloc] initWithCapacity: [sourceArray count]] ;
return destArray1;

In shuffle Method:

imageMArray=[[self shuffleOnlyArray:imageMArray] retain];

There appears to be a memory leak in the Shuffle method.

Should I release imageMArray or set it to nil? If it should be released, should it be autoreleased?

score 5 · Accepted Answer · edited May 23 '17 at 12:33

5

imageMArray=[[NSMutableArray alloc] initWithArray:CategoryImages];

In the above statement, you have a memoryleak. Instead you can have like as follows.

imageMArray = [NSMutableArray arrayWithArray:CategoryImages];

In ShuffleOnlyArray Method, return the autoreleased object.

NSMutableArray *destArray1 = [[NSMutableArray alloc] initWithCapacity: [sourceArray count]] ;
return [destArray1 autorelease];

But after you get it, retain (take the ownership) the array object.

imageMArray=[[self shuffleOnlyArray:imageMArray] retain];

Edit

In shuffle method, do as follows:

NSMutableArray *imageMArray1 = [imageMArray mutableCopy];
if( imageMArray )
{
   [imageMArray release];
}
imageMArray=[[self shuffleOnlyArray:imageMArray1] retain];
[imageMArray1 release];

Edit 2: One more solution:

Use the category to shuffle as mentioned in the SO link

No need of creating new and releasing the arrays.

edited May 23 '17 at 12:33

Community

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answered Mar 16 '12 at 07:32

Ilanchezhian

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Is it really necessary!! Yes you are right. Because when first I am just autoreleasing destArray.Not retaining It causes the crashes. – Arpit B Parekh Mar 16 '12 at 07:36
@Adhira: I have setted properties and synthesise then also I need to write retain because otherwise it will contain autoreleased objects... – Arpit B Parekh Mar 16 '12 at 07:40
Is good that you write him the code. But it will also be nice if he will understand why the code is like you written it and not like he was doing it. – Alex Terente Mar 16 '12 at 07:44
@ArpitParekh, before retaining another array in `shuffle` method, I am releasing the earlier retained array. See my Edit. – Ilanchezhian Mar 26 '12 at 10:45
But if I release it how can I use it to shuffle again..!!? – Arpit B Parekh Mar 26 '12 at 10:56

score 1 · Answer 2 · answered Mar 16 '12 at 07:31

1

1 You already have a memory leak in the following lines.

imageMArray = [[NSMutableArray alloc] initWithArray:CategoryImages];
imageMArray = [self shuffleOnlyArray:imageMArray];

In the first line you create an object with retain count 1. Then you say that your imageMArray pointer points to other object. You should release the first object, because you louse the reference to the fist object and you can not release it after you change the reference!

2 You should not use retain because your ShuffleOnlyArray method returns a retained object. Your factory method should return an autorelease object and the caller of the factory should decide if if will retain it or not.

Hope I was clear enough

answered Mar 16 '12 at 07:31

Alex Terente

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Hey but when should I release array because the method caontains the same array – Arpit B Parekh Mar 16 '12 at 07:34
When I change the refrence, where should I release it. – Arpit B Parekh Mar 16 '12 at 08:49
You can make the array autorelease as Aadhira did or you just call. [imageMArray release]; and then imageMarray = [self shuffleOnlyArray:imageMArray];. And take in mind that shuffleOnlyArray have to return auto relsease and you have to retain as Aadhira did imageMArray=[[self shuffleOnlyArray:imageMArray] retain]; – Alex Terente Mar 16 '12 at 10:54

NSMutableArray: Memory management while calling methods

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