memory management question -- releasing an object which has to be returned

Question

Hi,

I have an NSMutableArray called playlist. This is in a method called getAllPlaylists. The code is something like this:

-(NSMutableArray *)getAllPlaylists
{
    //playlist is an instance variable
     playlist = [[NSMutableArray alloc] init]; //memory leak here
    ...
    //some code here which populates the playlist array
    [playlist addObject: object1];
    ...
     return playlist;
}

The array allocation step of playlist is causing a memory leak. In such a scenario where can i release this array? Or can i avoid allocation n initialization of playlist here by doing something else? Any help will be greatly appreciated!!

Answer 1

2 solutions:

Use autorelease:

- (NSMutableArray*)getAllPlaylists
{
    playlist = [[NSMutableArray alloc] init];
    ...
    return [playlist autorelease];
}

or instead of using [[NSMutableArray alloc] init] to create your NSMutableArray object, use [NSMutableArray array] which is equivalent to [[[NSMutableArray alloc] init] autorelease]:

- (NSMutableArray*)getAllPlaylists
{
    playlist = [NSMutableArray array];
    ...
    return playlist;
}

Answer 2

You should autorelease newly created objects that you want to return that are not owned by the object (local variables, not instance variables).

playlist = [[[NSMutableArray alloc] init] autorelease];

Alternatively, you can use the convenience method to do that more easily:

playlist = [NSMutableArray array];

For items the object owns (instance variables), you should make sure you release the old value first and implement a dealloc method that also releases the value.

- (NSMutableArray*)getAllPlaylists {
    [playlist release];
    playlist = [[NSMutableArray alloc] init];
    return playlist;
}

- (void)dealloc {
    [playlist release];
    [super dealloc];
}

For more info, see the memory management guide.