Scroll between UIViewControllers without losing last state - ios

Question

I have ten different UIViewControllers with each containing a right and left button. The right arrow will bring the next controller in front while the left one will bring the previous one. I need to navigate between controllers without losing the last state. But every time, the right arrow is pressed, a new controller comes forward. I have tried pushController and presentController. I want to freely navigate between controllers without losing the state. Can you guide how to do it?

Answer 1

Questions like this are very broad, Cocoa Touch provides numerous mechanisms for managing view controllers. I suggest reading Apple's View Controller Programming Guide for iOS and in particular the Presenting View Controllers from Other View Controllers and Coordinating Efforts Between View Controllers sections.
That being said, here are two approaches to managing the flow of a number of UIViewControllers while keeping each alive so that all of their state (UI & underlying data) persist for the duration of their use. The key to both of these approaches is that a master view controller orchestrates the switching in and out of all of the UIViewControllers that need to be presented.
UINavigationController
Imagine your 10 view controllers 1 though 10. This approach is appropriate if the user is always presented view controller number 1 first and can only navigate sequentially forward and backwards through them i.e. the user cannot navigate between 1 and 10 directly:
A UINavigationController specialises in managing the navigation of hierarchical content. Although we may not think of our 10 view controllers as hierarchical conceptually, using a UINavigationController allows us to leverage its existing functionality for sequential navigation. In this model, each view controller is resposible for holding the reference to the following view controller in the sequence, presenting it and implementing its delegate callback to know when to dismiss it:
Code
MYPresentationViewController.h
#class MYPresentationViewController;
// The MYPresentationViewControllerDelegate allows the presenting view controller to know when the presented view controller (next highest in the presentation stack) has been dismissed.
#protocol MYPresentationViewControllerDelegate <NSObject>
- (void)viewControllerDidFinish:(MYPresentationViewController *)viewController;
#end
#interface MYPresentationViewController : UIViewController <MYPresentationViewControllerDelegate>
// The next view controller in the sequence.
#property (strong, nonatomic) MYPresentationViewController *nextViewController;
// The delegate responsible for showing and dismissing this view controller.
#property (assign) id<MYPresentationViewControllerDelegate> delegate;
#end
MYPresentationViewController.m
#import "MYPresentationViewController.h"
#implementation MYPresentationViewController
#pragma mark - Custom Property Assessors
// Returns the next view controller in the sequence. Creates and configures it if it doesn't already exist.
- (MYPresentationViewController *)nextViewController
{
if (_nextViewController == nil)
{
_nextViewController = [[MYPresentationViewController alloc] initWithNibName:#"MYPresentationViewController" bundle:nil];
_nextViewController.delegate = self;
}
return _nextViewController;
}
#pragma mark - UI Control Event Handlers
- (IBAction)leftButtonPressed:(UIButton *)sender
{
// Tell the delegate this view controller is ready to be dismissed.
[self.delegate viewControllerDidFinish:self];
}
- (IBAction)rightButtonPressed:(UIButton *)sender
{
// Present the next view controller.
[self.navigationController pushViewController:self.nextViewController animated:YES];
}
#pragma mark - MYPresentationViewControllerDelegate
- (void)viewControllerDidFinish:(MYPresentationViewController *)viewController
{
// Dismiss the next view controller to return to this one.
[self.navigationController popViewControllerAnimated:YES];
}
#end
Custom Master Controller
Imagine your 10 view controllers 1 though 10. This approach is appropriate if the user can be presented with a view controller that isn't at either end (1 or 10) first and/or the user can navigate between 1 and 10 directly allowing for a cyclical navigation:
Writing our own 'master controller' that overseers and facilites the switching in and out of all of the UIViewControllers that need to be presented allows us to implement the navigation in any way we want. In this model, the master view controller is responsible for handling the references to all of the view controllers being presented, presenting them and implementing their delegate callbacks:
Code
MYMasterViewController.h
#import "MYPresentationViewController.h"
#interface MYMasterViewController : UIViewController <MYPresentationViewControllerDelegate>
// The collection of view controllers to be presented.
#property (strong, nonatomic) NSArray *allViewControllers;
#end
MYMasterViewController.m
#import "MYMasterViewController.h"
#implementation MYMasterViewController
...
// Create 10 view controllers;
- (void)createViewControllers
{
NSMutableArray *allViewControllers = [NSMutableArray arrayWithCapacity:10];
// Create our 10 view controllers.
for (int i = 0; i < 10; i++)
{
MYPresentationViewController *viewController = [[MYPresentationViewController alloc] initWithNibName:#"MYPresentationViewController" bundle:nil];
viewController.delegate = self;
viewController.index = i;
[allViewControllers addObject:viewController];
}
self.allViewControllers = allViewControllers;
}
// Display first view controller, could be any in the sequence.
- (void)displayViewController
{
MYPresentationViewController *firstViewController = [self.allViewControllers objectAtIndex:0];
[self presentViewController:firstViewController animated:NO completion:nil];
}
#pragma mark - MYPresentationViewControllerDelegate
- (void)viewController:(MYPresentationViewController *)viewController didDismissWithButton:(kButtonPressed)button
{
[self dismissViewControllerAnimated:NO completion:nil];
// Determine the next view controller to display.
NSInteger index = viewController.index;
index += button == kButtonPressedLeft ? -1 : 1;
if (index < 0) {
index = self.allViewControllers.count - 1;
}
else if (index >= self.allViewControllers.count) {
index = 0;
}
MYPresentationViewController *nextViewController = [self.allViewControllers objectAtIndex:index];
[self presentViewController:nextViewController animated:NO completion:nil];
}
#end
MYPresentationViewController.h
#class MYPresentationViewController;
// Enumeration used to give a more descriptive code association with the presentation view controller's navigation button options.
typedef enum {
kButtonPressedLeft,
kButtonPressedRight,
} kButtonPressed;
// The MYPresentationViewControllerDelegate allows the presenting view controller to know when the presented view controller has been dismissed and with what button i.e. (left or right).
#protocol MYPresentationViewControllerDelegate <NSObject>
- (void)viewController:(MYPresentationViewController *)viewController didDismissWithButton:(kButtonPressed)button;
#end
#interface MYPresentationViewController : UIViewController
// The index of this view controller in relation to 10.
#property (assign) NSInteger index;
// The delegate responsible for showing and dismissing this view controller.
#property (assign) id<MYPresentationViewControllerDelegate> delegate;
#end
MYPresentationViewController.m
#import "MYPresentationViewController.h"
#implementation MYPresentationViewController
#pragma mark - UI Control Event Handlers
- (IBAction)leftButtonPressed:(UIButton *)sender
{
// Tell the delegate this view controller is ready to be dismissed.
[self.delegate viewController:self didDismissWithButton:kButtonPressedLeft];
}
- (IBAction)rightButtonPressed:(UIButton *)sender
{
// Tell the delegate this view controller is ready to be dismissed.
[self.delegate viewController:self didDismissWithButton:kButtonPressedRight];
}
#end

Answer 2

You need to maintain a stack of view controllers, similar to what UINavigationController does. When you move to the right, instead of creating a new view controller to present, you just get the next view controller in the array and present it
Then to maintain state each view controller should be responsible for managing its own state, and since you are not creating new controllers each time the state will be the same after a view has been removed and then presented again.
e.g. instead of
UIViewController *controller = //new view controller
[self presentViewController:controller];
you should do
UIViewController *controller = [self.controllers nextViewController];
[self presentNextController:controller];