Question

I’m looking for a technique to progressively load in the contents of a UIViewController to make an app feel “snappier”. I noticed this issue when pushing a viewcontroller onto the stack there’s a noticeable delay while waiting for it to push in. The UIViewController’s View has some complex subviews with transparency. I’m wondering if I create them after viewDidAppear and ‘fade’ them in, then the transition will appear much smoother.

I noticed a similar effect in Apple’s Trailers app. When tapping a movie in that app the detail view pushes in and the contents load after the fact. Granted part of that delay is because they are downloading the details before showing them, but it seems like they always fadein that large image whether it’s been downloaded already or not.

Has anyone had much success with this or with improving UIViewController loads in general.

Answer 1

Before you start making changes in an effort to improve performance, use Instruments to profile your app and find out where the problem really is. Is it in drawing the complex subviews? Is it in loading the data? The only way to know is to measure.

There’s no reason you couldn’t do as you propose — have the view controller create/load its main view and then add the complex subviews afterward. Your view controller can add and remove subviews at will. Will that make the app feel snappier? It might — it’s similar to the default image strategy Apple built into iOS, where the OS loads a picture of your interface to make the device seem responsive, and then substitutes the real interface once that’s ready. On the other hand, if the user still has to wait for the complex subviews to be created before the view is useful, seeing the rest of the view might not help much.

Another possibility (again, after measuring) might be to create the views before the user needs them. This runs counter to the lazy initialization that iOS apps commonly use to conserve memory and power, but if you know that you’re going to need the views and you can expect a lull in user activity before they’re needed, it could be a good way to increase the app’s apparent speed. All you need to do to get a view controller to create/load its view is to access its view property.