Question

I try to understand the memory management in ObjectiveC and still some things are a misery for me.
I’ve got an instance variable:

    NSMutableArray *postResultsArray;

when a button is clicked in the UI I create new array:

self.postResultsArray = [NSMutableArray array];

then I add some objects to the array and when the whole operation is done I would like to release the array:

[self.postResultsArray release];

(I assume that all the objects stoed in the array will be released along with the array).
The problem appears when I click the button again and in the code I want to create the array again with:

self.postResultsArray = [NSMutableArray array];

I get:

[CFArray release]: message sent to deallocated instance 0x3d9e390

Can’t I initialize the same instance variable for the second time? or maybe I should not release it? and if so, why?

Thanks!

Answer 1

Don’t to this:

[self.postResultsArray release];

When you do this, the ivar is still assigned to the old array’s memory address. If you want to release the array, there are two safe ways to do it:

[postResultsArray release];
postResultsArray = nil;

Or

self.postResultsArray = nil;

What’s happening is that the code for setting the postResultsArray looks like this (paraphrase, not exact):

-(void)setPostResultsArray:(NSMutableArray *)newArray {
    [array retain];
    [postResultsArray release]; // this is what's causing the the deallocation message in your log
    postResultsArray = array;
}