Switch views and retain data

badnewsbeers · 12-09-2011, 01:54 PM

Hi,
I'm writing a procedure based application where the user navigates through a set of views and makes changes on them (toggle switches, buttons, etc). All is well and good, except when the user navigates backwards through the views and then tries to move forward again - all the views are reset.

I am wondering if there is a way to set up my software such that anytime a user leaves a view, all of its data is retained until either the user returns to that view and modifies it or the procedure is complete and the data saved.

Thanks in advance!

BrianSlick · 12-09-2011, 01:58 PM

Nope, not possible. Pay no attention to every single app ever made.

badnewsbeers · 12-09-2011, 02:02 PM

If you could point me in the right direction, that would be fantastic.

BrianSlick · 12-09-2011, 02:03 PM

Google for "iphone sdk how to save data?"

badnewsbeers · 12-09-2011, 02:16 PM

Perhaps I wasn't very clear. I'm more concerned with the state of the objects on the screen. For example, if the user were to flip a few toggle switches, move a few screens, realize they made an error, and then go back to the beginning, I'd like those toggles to remain in the state they were in. Perhaps I just have a misunderstanding of MVC but I'm not sure how to make this happen. Basically I'd like a way to prevent the views from popping off the stack as the user backtracks through the application. If you're saying the same thing as me then I apologize and will keep looking.

BrianSlick · 12-09-2011, 02:18 PM

Do you have an M somewhere in this equation?

badnewsbeers · 12-09-2011, 02:21 PM

Not specifically defined, I was doing it within the views. Assuming this is the wrong way to approach things. Back to the books.

BrianSlick · 12-09-2011, 02:22 PM

You can't rely on views for storage. Off-screen views are routinely unloaded to free up memory. Capture whatever information needs to be saved when the view goes off screen. Restore it when the view comes back on screen.

Duncan C · 12-09-2011, 02:39 PM

Quote:

Originally Posted by badnewsbeers

Not specifically defined, I was doing it within the views. Assuming this is the wrong way to approach things. Back to the books.

Here's what to do:

Set up a data container singleton. At launch, create all your view controllers and save pointers to them in the singleton. That will cause you view controllers to stick around. When you need to push a view controller, fetch the existing view controller from the singleton and push it.

In each view controller's viewDidLoad method, set all the view settings the way you want them to be, using the view controller's instance variables, or a separate model object, if you have it separated out.

Make your view controllers respond to a low memory warning by releasing everything they can reproduce.

Your view controllers will stick around for the life of your application. Their views could be unloaded at any point when they are not frontmost, which is why you write code in your viewDidLoad that completely sets up your views.

badnewsbeers · 12-09-2011, 03:41 PM

Thanks very much guys, I appreciate it. That's exactly what I'll do.