Multiple Views within one XIB - iPhone SDK

Answer 1

It's a question of memory optimization and loading times. If you put all your views in one XIB, then when your application launches, it has to load the entire XIB into memory and construct all of the objects for all of the controls, and this takes a non-trivial amount of time.

If instead you separate your views into separate XIBs, then your app will start up much faster, because only the XIB containing the initial view will be loaded, and it will also use less memory at first. Then, when the view changes, you can load the XIB containing the new view lazily. This will incur a minor hitch when opening a view for the first time. If you're really trying to optimize memory use, you can also unload the previous view when switching views, but I wouldn't recommend this, as this will incur a hitch every time you switch views, instead of just the first time you switch to any given view.

Answer 2

Following up on the previous answer, there are some times when you would like to load multiple views at the same time. Here's an example: You are displaying a report with multiple pages and you're going to use a UIScrollView to manage them. When the user is done browsing the report, he will close the report which will dismiss the view.

Create a UIScrollView in a XIB along with a UIView for each page you need. Since the UIViews are part of the XIB, they will be loaded into memory together, all at once, when the report is opened. Create two UIViewControllers and use them to display the page being viewed and the one being scrolled to. As the user moves through the pages, re-use the UIViewController on the page being scrolled away from to hold the page being scrolled to.

This will ensure great performance while the user is flipping through the pages. It loads all the pages at once up front into memory. I only uses two UIViewControllers, and it just changes which views are in them and moves them around.

This also has the great benefit of having all of the pages in one XIB. It makes it easier to edit, and quicker to load than separate XIB's. You just have to make sure you have the memory to load all the pages at once. If it's static content (such as in my case) it's a great way to go.

If you're looking for a good example of how to do this, I found this resource to be an excellent starting point:

http://cocoawithlove.com/2009/01/multiple-virtual-pages-in-uiscrollview.html