Slow performance for presentViewController - depends on complexity of presentING controller?

Question

I am presenting a view controller:

SCAAboutController2 *controller = [[SCAAboutController2 alloc] initWithNibName:nil bundle:nil];
UINavigationController *navCon         


        

Answer 1

Your app is unresponsive because of several add and remove operation on a set. If you do any heavy processing on main thread the app gets block and becomes unresponsive.

Short ans is you have a loop which is adding objects in a set and its doing that on the main thread which is making your app slow.

If you look at your instruments the view loading buttons and rendering is pretty fast. initWithFrame , viewDidLoad is taking less than 4% of overall of time. The majority of the time is taken by NSISVairable release and retain which is done around 500 times. So you are doing something with your collection object and probably its in a loop. retain and release takes time and should not be done on main thread.

Simple solution is :

dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
  // do all the heavy lifting here in background thread. 
}

Why does the following code does not improve anything :

dispatch_async(dispatch_get_main_queue(), ^{
        SCAAboutController2 *controller = [[SCAAboutController2 alloc] initWithNibName:nil bundle:nil];
        UINavigationController *navController = [[UINavigationController alloc] initWithRootViewController:controller];
        [self presentViewController:navController animated:YES completion:nil];
    });

because you are already doing this stuff in main thread and you need to call main_queue on in background thread. You should not do any UI stuff on background thread.