NsMutable array retain count

Question

i used the instruments to find leaks in my iphone app and i found that i have leak in this line in my code

tableViewController.dataSource = [[NSMutableArray alloc] initWithArray:[subjects_dic allKeys]];

the property dataSource defined as retain. is this a mistake ?!

Answer 1

Break it up:

NSMutableArray *mutArray = [[NSMutableArray alloc] initWithArray:[subjects_dic allKeys]];
[tableViewController setDataSource:mutArray];
[mutArray release];

It's the same pattern you use for creating, pushing, and releasing Views from the Navigation Controller.

Answer 2

If you specify retain in your property declaration, then anything you assign to that property will be retained.

So in your example, you have two options:

1. Instead of creating a new array with the alloc/init approach, you can simply use [NSMutableArray arrayWithArray:[subjects_dic allKeys]];

2. Release the property once after setting it. This option isn't as good an idea, as it may cause a crash if the property's memory management is changed in the future and this release is forgotten about.

I'd recommend option 1.

Answer 3

Another alternative:

// mutableCopy implicitly retains the array returned by allKeys
NSMutableArray *mutArray = [[subjects_dic allKeys] mutableCopy];
[tableViewController setDataSource:mutArray]; // @property dataSource retains mutArray
[mutArray release];