How come the completion block for this CATransaction never fires?
[CATransaction begin];
[CATransaction setCompletionBlock:^{
// table animation has finished
NSLog(@"why does this section never execute?");
}];
[self.tableView beginUpdates];
[self.tableView reloadRowsAtIndexPaths:@[[NSIndexPath indexPathForRow:self.currentFeedItems.count inSection:0]] withRowAnimation:UITableViewRowAnimationFade];
[self.tableView endUpdates];
[CATransaction commit];
The tableview animation works, but the completion block is never executed. The Apple documentation says that the completion block is guaranteed to execute.
Oh boy, this was so obscure I'm actually amazed I found the problem.
The cell that was being reloaded contains a UIActivityIndicatorView, which worked fine. When the cell reloads it implicitly redraws the table cell and a startAnimating call happens within that process in the table cell. Somehow that startAnimating call interferes with the CATransaction completion block.
When I wrap the startAnimating call in a dispatch_async block, the problem goes away: