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POUITableViewCell bad performance with AutoLayout
 

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    <p>I'm somewhat stuck with this one… any help is very appreciated. I've already spent lots of time debugging this.</p> <p>I've got <code>UITableView</code> with data source provided by <code>NSFetchedResultsController</code>. In a separate view controller I insert new records to the CoreData using <code>[NSEntityDescription insertNewObjectForEntityForName:inManagedObjectContext:]</code>, save the managed object context and dismiss that controller. Very standard stuff.</p> <p>The changes in managed object context are then received by <code>NSFetchedResultsController</code>:</p> <pre><code>- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller { [self.tableView beginUpdates]; } - (void)controllerDidChangeContent:(NSFetchedResultsController *)controller { [self.tableView endUpdates]; } - (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath { switch (type) { case NSFetchedResultsChangeInsert: [self.tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationNone]; break; case NSFetchedResultsChangeDelete: [self.tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone]; break; case NSFetchedResultsChangeUpdate: [self.tableView reloadRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone]; break; case NSFetchedResultsChangeMove: [self.tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone]; [self.tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationNone]; break; } } </code></pre> <p>And this is where the problem appears — it takes too long(about 3-4 seconds on an iPhone 4) to do that. And it seems like the time is spent calculating layout for the cells.</p> <p>I've stripped everything from the cell(including custom subclass) and left it with just <code>UILabel</code>, but nothing changed. Then I've changed the style of the cell to Basic(or anything except Custom) and the problem disappeared — new cells are added instantaneously.</p> <p>I've doubled checked and <code>NSFetchedResultsControllerDelegate</code> callbacks are called only once. If I ignore them and do <code>[UITableView reloadSections:withRowAnimation:]</code>, nothing changes — it is still very slow.</p> <p>It seems to me like Auto Layout is disabled for the default cell styles, which makes them very fast. But if that is the case — why does everything loads quickly when I push the <code>UITableViewController</code>?</p> <p>Here's the call trace for that problem: <img src="https://i.stack.imgur.com/z2hCd.png" alt="stack trace"></p> <p>So the question is — what is going on here? Why are cells being rendered so slowly?</p> <p><strong>UPDATE 1</strong></p> <p>I've built a very simple demo app that illustrates the problem I'm having. here's the source — <a href="https://github.com/antstorm/UITableViewCellPerformanceProblem" rel="noreferrer">https://github.com/antstorm/UITableViewCellPerformanceProblem</a></p> <p>Try adding at least a screenful of cells to feel the performance problems.</p> <p>Also note that adding a row directly ("Insert now!" button) is not causing any slowness.</p>
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    1. USAnthony Dmitriyev
    1. USAnthony Dmitriyev
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    1. COJust to confirm - you ARE assigning your custom cells a unique identifier and dequeueing them instead of re-creating, correct?
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    2. COand what auto-layout rules are specified on the cell?
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    3. COYes, I am assigning a unique identifier and dequeueing cells using `[UITableView dequeueReusableCellWithIdentifier:forIndexPath:]`.
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      1. USAnthony Dmitriyev
 

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