How to save/restore view state in iOS?

Question

I'm using the ECSlidingViewController to create a slide out menu (like Facebook).

I have this storyboard:

As you can see, I have a navigation controller. I have a major problem though, that even the official demo created by the user who made that controller didn't implement: it doesn't save the state of the view controller when changing views and then coming back .

So, for example, the orange view will always be the first view when I open the app, it gets viewDidLoad . Then I switch to my green view (the second one), and click the button. It changes the background color of that view to red. Then if I go back to my first view, and then back to the second one, the background color of the latter is green again. I want it to stay red.

This is my code to switch views (in MenuViewController ):

(void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    // Get identifier from selected
    NSString *identifier = [NSString stringWithFormat:@"%@", [self.menu objectAtIndex:indexPath.row]];

    // Add the selected view to the top view
    UIViewController *newTopVC = [self.storyboard instantiateViewControllerWithIdentifier:identifier];

    // Present it 
    [self.slidingViewController anchorTopViewOffScreenTo:ECRight animations:nil onComplete:^{        
        CGRect frame = self.slidingViewController.topViewController.view.frame;
        self.slidingViewController.topViewController = newTopVC;
        self.slidingViewController.topViewController.view.frame = frame;
        [self.slidingViewController resetTopView];

    }];
}

As you can see, it's always instantiating a new VC every time. I want it to save the VC, create the new one if it's not created, then show that one. If the user goes back to a view that has already been created, it should just restore the saved view, not create a new one.

I have put the Init View Controller in a Navigation Controller, now how can I implement this save/restore mechanism for my views? I'd like it to work with 2,3,4, etc....as many views as possible.

Thanks.

Answer 1

When you go "back" you essentially pop the viewcontroller from the navigationstack. At that point there are no more references to that viewcontroller and it get's deallocated and as a result you loose all your changes.

You can handle this a couple of ways:

1) Keep a reference to red/green viewcontroller alive in the parent viewcontroller (the one that is presenting) and use that instead of instantiating a new one. This is not very memory friendly but can be used if used sparingly.

in the interface put:

@property (nonatomic, strong) UIViewController* myGreenController;

then change instantiation to

if (!self.myGreenController)
{
   self.myGreenController = [self.storyboard instantiateViewControllerWithIdentifier:identifier];
}
...
self.slidingViewController.topViewController = self.myGreenController;

2) Ideally implement a delegate pattern to pass state back to the parent viewcontroller (something like How do I set up a simple delegate to communicate between two view controllers? ). Then next time when you need the viewController you set the state before presenting it.