UIPageViewController and saving the state of the UIViewControllers - ios

Question

I am pretty new to UIPageViewControllers. I have setup one that can page through different types of UIViewControllers.
I have noticed that when I scroll back to a previous one all the data and states are reset (i.e. I previously changed the UIViewController background color and it has reset back to default). I am using restoration IDs from the story board to initiate these controllers.
If I am using these shouldn't it save the state of the controller?
Code for changing controllers:
#pragma mark - UIPageViewControllerDataSource
- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerBeforeViewController:(UIViewController *)viewController
{
//This is nice and avoids having to use a counter
NSString *vcRestorationID = viewController.restorationIdentifier;
NSUInteger index = [self.controllerRestorationIDs indexOfObject:vcRestorationID];
if (index == 0) {
return nil;
}
return [self viewControllerAtIndex:index - 1];
}
- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController
{
NSString *vcRestorationID = viewController.restorationIdentifier;
NSUInteger index = [self.controllerRestorationIDs indexOfObject:vcRestorationID];
//Don't allow it to go forward if there is one at the end
if (index == self.controllerRestorationIDs.count - 1) {
return nil;
}
return [self viewControllerAtIndex:index + 1];
}
#pragma mark - Private Methods
- (UIViewController *)viewControllerAtIndex:(NSUInteger)index
{
// Only process a valid index request.
if (index >= self.controllerRestorationIDs.count) {
return nil;
}
// Create a new view controller.
BaseContentViewController *contentViewController = (BaseContentViewController *)[self.storyboard instantiateViewControllerWithIdentifier:self.controllerRestorationIDs[index]];
// Set any data needed by the VC here
contentViewController.rootViewController = self;
return contentViewController;
}
Is there a way to do this so the state is saved and the controllers aren't reloaded every time?

Answer 1

This behavior happens because you instanciate a new view controller each time you access it.
To solve this :
you can cache the view controllers : store them in a global mutable array of your page view controller, and check each time the page view controller asks its data source for a view controller, add it to the global array or retrieve it if it's already in there.
use class variables instead of instance variables for the properties you change in the view controllers.
The first solution is volatile : whenever the pageVC is deallocated, you'll lose the modification made to the view controllers. The second one is more sure.