When do custom table view cells dealloc?

Question

I was under the impression that table view cells never got dealloced until the app crash because you are able to resuse them. But when I was profiling my table view, I realized that something was calling dealloc on my custom cell. What exactly dealloc's custom cells and can I stop it?

Answer 1

Using the common "reuse" pattern:

- (UITableViewCell *)tableView:(UITableView *)tv cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    static NSString *cellId = @"Foo";
    UITableViewCell *cell = [tv dequeueReusableCellWithIdentifier:cellId];
    if (!cell) {
        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellId]
                autorelease];
    }
    // update the cell content
    return cell;
}

The table view creates as many cells as required to fill the its frame height.
When disappearing from screen they are removed from the view and put in the reuse queue, thus not deallocated.

All the cells are dealloc'd when the tableView is dealloc'd and some cells may be dealloc'd when you number of rows changes (say you had 20 cells before and only 2 after update).

You might be tempted to get rid of cells reuse but you would lose all the magic done behind to keep a low memory footprint and to have a smooth scrolling experience.