Question

I’m beginning to get my head round all the memory management stuff, but I’m a bit puzzled by the use of properties with arrays. If I declare the property in the interface like so –

@property (nonatomic,retain) NSMutableArray *myArray;

then synthesize it in the implementation, do I need to alloc it when I create the array? Like so –

self.myArray = [[NSMutableArray alloc] init];

or does this result in an extra retain count? Should I just do –

self.myArray = [NSMutableArray array];

and let the setter do the retaining?

Many thanks to anyone who can clarify this for me!

Answer 1

In both cases you are letting the setter retain your instance.

In this case you are overretaining:

self.myArray = [[NSMutableArray alloc] init];

The setter does and the alloc message sent.

This can be fixed with:

self.myArray = [[[NSMutableArray alloc] init] autorelease];

or

NSMutableArray *newInstance = [[NSMutableArray alloc] init];
self.myArray = newInstance;
[newInstance release];

This is fine

self.myArray = [NSMutableArray array];

however not every class has a convenience class method to return an autoreleased instance.

Have a look at the Memory Management Programming Guide / Object Ownership and Disposal, this will give you a good understanding about when the retain counts increases and when you should release.