Question

I’m really frustrated at this point. Dequeueing a reusable cell with identifier is always returning null.

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{
    static NSString *CellIdentifier = @"Cell";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if(cell == nil) {
        NSLog(@"INIT");
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
    }
    return cell;
}

What am i doing wrong here? Thanks.

Answer 1

You’re doing everything right, everything is working as it should. iOS will create enough new cells to fill the screen (plus one). It will start reusing these cells only when your UITableView contains more rows than can fit on one screen and then the user scrolls.

You’ll find that if you have a datasource will say, 100 items in it and then scroll, you’ll only have your log message show probably 11 times (depends on how many cells fit on your screen) instead of 100 as iOS will start recycling cells as you scroll.

With large lists, it would use too much memory to create new views for every possible row in a UITableView. The alternative would be to allocate new views for rows as you scroll. However, this would create a performance bottleneck that would cause laggy scrolling in any UITableView.

Apple mention the performance bottleneck in their documentation on UITableViews.

Reuse cells. – Object allocation has a performance cost, especially if the allocation has to happen repeatedly over a short period—say, when the user scrolls a table view. If you reuse cells instead of allocating new ones, you greatly enhance table view performance.