Question

I have a problem with my code that for the life of me I can’t figure out, not even with all previous threads here on SO.
I’m pulling data from a JSON source and putting it in an NSDictionary as stated in tutorials and on SO. When profiling the app, I notice a memory leak caused by this NSDictionary but releasing it at the end of this function crashes the app. Any suggestions?
(By the way: I’m new to Obj-C and programming in general, so this code is mostly cherrypicked from various sources.)

- (void)fetchedData:(NSData *)responseData {
    //parse JSON for empty return
    if([responseData length] != 0){

        NSError* error = nil;
        //Convert JSON data to Obj-C
        NSDictionary* allShotData = [NSJSONSerialization JSONObjectWithData:responseData options:kNilOptions error:&error];

        NSString *player = [[allShotData objectForKey:@"player"] objectForKey:@"name"];
        NSString *shotDribbblePage = [allShotData objectForKey:@"url"];

        NSString *shotTitle = [allShotData objectForKey:@"title"];
        NSURL *imageURL = [NSURL URLWithString:[allShotData objectForKey:@"image_url"]];
        shotPageURL = [shotDribbblePage retain];


        //***********************
        //  Setup a-sync loading of shot
        //***********************

        NSOperationQueue *queue = [NSOperationQueue new];
        NSInvocationOperation *operation = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(loadImage:) object:imageURL];   
        [queue addOperation:operation]; 
        [operation release];
        [queue release];
    }
    else{
        airballCount++;
        if (airballCount <= 20) {
            [self getDribbbleData];
        }
        else{
            NSLog(@"Too many airballs. Bailing out");
            [self showNoConnectionModal];
        }
    }
}

Answer 1

Here:

shotPageURL = [shotDribbblePage retain];

you should probably use the accessor:

self.shotPageURL = shotDribbblePage;

I should really emphasize that you should use your accessors everywhere since they do your ref counting for you (exception: not in initializers and dealloc). As beryllium also notes, you could do your ref counting manually if there is no accessor. That takes the basic form:

[shotPageURL release];
shotPageURL = [shotDribbblePage retain];

If it’s the contents of the returned dictionary that are leaking, then it’s how you have used/referenced the contents when read (over-retain).

If you’re using your class in a concurrent context, then you will usually need a lock.

If you’re loading a UIImage or otherwise interacting with UIKit objects from a secondary thread — that’s not good.