show activity indicator while loading ViewController
<p>I have a ViewController that takes time to load its views.  When I run Instruments, I see from the home screen, if I tap on the icon that pushes that view controller onto the stack, it's half laying out the views, and half getting the data for the views.  I tried adding an activity indicator to display on the home screen over the button when the button is pressed to push the LongRunningViewController onto the stack.  So I basically do this:</p>

<pre><code>- (IBAction)puzzleView:(id)sender {
    dispatch_async(dispatch_get_main_queue(), ^{
        [self.activityIndicator startAnimating];
    });

    PuzzleViewController *detailViewController = [[[PuzzleViewController alloc] init] autorelease];
    [self.navigationController pushViewController:detailViewController animated:YES];
    [self.activityIndicator stopAnimating];
}
</code></pre>

<p>The home screen lags while pressing the button, and then loads the view.  I'm trying to show the activity indicator while the other screen is preparing to be pushed (or at least that's the way I think it works).  The activity indicator does not show however.  I'm wondering if this can be done?  Or do other apps push their ViewController, and then on that screen, they have the activity indicators showing the loading of their different resources?</p>
