Delay in presenting a modal view controller

Question

I have a tab bar based app. There are navigation controllers in all 5 tabs with instances of custom view controller setup properly as root view controllers. This loads just

Answer 1

I have also had this strange delay when presenting from tableView:didSelectRowAtIndexPath: looks like an Apple bug.

This solution seems to work well though.

CFRunLoopWakeUp(CFRunLoopGetCurrent()); // Fixes a bug where the main thread may be asleep, especially when using UITableViewCellSelectionStyleNone

Answer 2

It seems calling presentViewController:animated:completion from within tableView:didSelectRowAtIndexPath: is problematic. It's difficult to find anything that stands out when using the Time Profiler in Instruments, also. Sometimes my modal view comes up in less than a second and other times it takes 4s or even 9s.

I think it's related to the underlying UIPresentationController and layout, which is one of the few things I see when selecting the region of time between tapping on a row and seeing the modal presentation in the Time Profiler.

A Radar exists describing this issue: http://openradar.appspot.com/19563577

The workaround is simple but unsatisfying: delay the presentation slightly to avoid whatever contentious behavior is causing the slowdown.

dispatch_async(dispatch_get_main_queue(), ^{
   [self presentViewController:nav animated:YES completion:nil];
});

Answer 3

The common problem with this behaviour is as follows:

one sets selectionStyle = .none for a cell in the tableView (it seems that it doesn't depend on UITableViewController subclassing as was written at http://openradar.appspot.com/19563577) and uses at the delegate method

override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath)

animating deselect

tableView.deselectRow(at: indexPath, animated: true)

which implies animation for non-animating cell.

In this case the subsequent view controller presentation has a delay.

There are some workaround solutions including dispatch_async on main thread, but it is better not to call deselectRow even without animation on unselectable cells in your code.