Question

I have a ViewController defined as follows:

@interface SectionController : UITableViewController {
   NSMutableArray *sections;
}
- (void) LoadSections;

When LoadSection is call it makes a call to NSURLConnection to load a url which in turn calls

    - (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    NSString *responseString = [[NSString alloc] initWithData:responseData encoding:NSUTF8StringEncoding];

    [connection release];
    [responseData release];

    NSDictionary *results = [responseString JSONValue];
    NSMutableArray *jSections = [results objectForKey:@"Items"];
    sections = [NSMutableArray array];

    for (NSArray* jSection in jSections)
    {
        Section* section = [Section alloc];
        section.Id = [jSection objectForKey:@"Id"];
        section.Description = [jSection objectForKey:@"Description"];
        section.Image = [jSection objectForKey:@"Image"];
        section.Parent = [jSection objectForKey:@"Parent"];
        section.ProductCount = [jSection objectForKey:@"ProductCount"];
        [sections addObject:section];
        [section release];
    }

    [jSections release];
    [results release];

    [delegate sectionsLoaded];

    [self.view reloadData];
}

The data parses correctly and I now have sections filled with many items.

Calling [self.view reloadData] forces a callback to the delegate method cellForRowAtIndexPath which should then present the data into the cell however its at this point that sections is now nil again.

Can someone please point out my mistake? I must admit I am a newbie to objective c and it probably a pointer issue. What is need to do is retain the value of sections after calling reloadData.

Many thanks.

Answer 1

Seeing the new code the problem is obvious:

sections = [NSMutableArray array];

should become

[sections release];
sections = [[NSMutableArray alloc] init];

note that the array does not become again “nil”, is instead deallocated and you get an invalid reference, which might (should) generate a crash on dereferencing.

I suggest you to read some articles on reference counted memory management as it might be not obvious if you are new to Objective-C, and often leads to mistake (i.e: autorelease is not magic at all)