Question

I have a problem with leaking custom cells.

In my overridden UITableViewController, I have,

- (UITableViewCell *)tableView:(UITableView *) tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
     TwitterTweetTableCell *cell = nil;

     // Obtain the cell...

    cell = [[TwitterTweetTableCell alloc]
            initWithTable:tableView
                andTweet:[[self getTimeline] objectAtIndex:indexPath.row]];

    return [cell autorelease];
}

And in the corresponding overridden UITableViewCell class,

- (TwitterTweetTableCell *) initWithTable:(UITableView *) tableView
    andTweet:(NSDictionary *) tweet
{

    tweetCell = nil;

    // ************************************************************************************
    // The identifier used in the following dequeue is the one set in the corresponding nib
    // ************************************************************************************

    tweetCell = (TwitterTweetTableCell *)
        [tableView dequeueReusableCellWithIdentifier:@"tweetCell"]; // <-- set this in NIB

    if (tweetCell)
    {
        NSLog(@"tweetCell: Reuse!");
    }

    if(!tweetCell)
    {
        NSArray *topLevelObjects = [[NSBundle mainBundle]
                loadNibNamed:@"TwitterTweetTableCell" owner:nil options:nil];

        for(id currentObject in topLevelObjects)
        {
            if([currentObject isKindOfClass:[TwitterTweetTableCell class]])
            {
                tweetCell = (TwitterTweetTableCell *)currentObject;

                break;
            }
        }

        // yadda, yadda, yadda

        [tweetCell retain];
    }

    return tweetCell;
}

There is a corresponding NIB for the custom cell (TwitterTweetTableCell), and as noted in the code, the Identifier for the cell is set to ‘tweetCell’ in there.

The code works fine except, according to Instruments, it leaks cells 🙁

I believe I’m correct in returning the cell with a retainCount of 1 (it’s a return from an alloc and, anyway, if I don’t it crashes with a zombie). As the code shows, I then autorelease it before finally handing it off to the table controller.

Thoughts on why this leaks would be appreciated.

Answer 1

The problem here is that in cellForRowAtIndexPath: you are allocating memory for a new instance of your custom cell, but in the initializer for your custom cell, you never actually use that memory you allocate, since you don’t return self, and instead return a reusable existing cell or instantiate a new one from a nib.

Since you’re initWithTable:andTweet: method isn’t really an initializer, you should just change it to being a convenience method that returns autoreleased instances instead. Change the method signature,

+ (TwitterTweetTableCell *) cellWithTable:(UITableView *) tableView
andTweet:(NSDictionary *) tweet

make it autorelease its return value,

return [tweetCell autorelease];

and then make a slightly different call to it in cellForRowAtIndexPath: and you’ll be all set:

return [TwitterTweetTableCell cellWithTable:tableView
                                   andTweet:[[self getTimeline] objectAtIndex:indexPath.row]];