Amending UINavigationController viewControllers stack before animation - ios

Question

I have an app where you can customize products to varying degrees. In some cases the options are split to two views, while in some other cases the first step isn't necessary.
What I would like is to treat all products the same and push the first customization step view controller to the navigation controller stack, let that view controller decide whether or not this step is necessary. If it is not necessary I want it to apply some default options to the product and immediately skip (before the transition animation) to step 2 while not allowing the user to back up to the first step.
The normal UINavigationController.viewControllers stack may look like this when at step 2:
[ListView (root)] -> [CustomizeStep1] -> [CustomizeStep2]
But I want it to apply the default values to the product and amend the view controller stack so that:
[ListView (root)] -> [CustomizeStep1]
----- becomes -----
[ListView (root)] -> [CustomizeStep2]
What I've tried is to use code like this in the CustomizeStep1 view controller:
- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
if (shouldSkipToStep2) {
UINavigationController *navController = self.navigationController;
// Move directly to step 2
UIStoryboard *storyboardLoader = [UIStoryboard storyboardWithName:#"Main" bundle:nil];
UIViewController *customizeStep2VC = [storyboardLoader instantiateViewControllerWithIdentifier:#"customizeStep2"];
// Replace current view contoller
NSMutableArray *viewHierarchy = [NSMutableArray arrayWithArray:navController.viewControllers];
[viewHierarchy removeObject:self];
[viewHierarchy addObject:customizeVC];
// Apply new viewController stack
[navController setViewControllers:viewHierarchy animated:NO];
}
}
If I take a look at the navigation controller's viewControllers array after this has been set, everything looks as expected.
What happens in iOS 7
When doing this, the entire functionality of the UINavigationController breaks. The CustomizeStep1 view controller still animates in but is nonfunctional. Tapping the back button still shows CustomizeStep1. Trying to interact with the view controller crashes the app. (It works as expected if the view controller is displayed without the sliding transition, though.)
What happens in iOS 8
The CustomizeStep1 view controller still animates in, but immediately after the transition ends it snaps over to show CustomizeStep2. Other than that it works as intended.
So, my question is if there is a better place to add the code to amend the view controller stack on the navigation controller?
I obviously need to wait until the view controller has been added to the navigation controller, otherwise I can't replace the view controller in the stack. However, I need to be able to cancel the transition animation so that I can animate in CustomizeStep2 instead.
I appreciate if this is impossible, just wanted to check if anyone knows a good way around this.
Edit:
How I would like it to ideally appear to the user

Answer 1

Instead of viewWillAppear:, use viewDidAppear: which is called after the animation finishes.
You could have a boolean on your view controller denoting whether it is filled in or not:
#interface ViewControllerOne : UIViewController
#property (nonatomic, assign, getter = isInitiallyFilledIn) BOOL initiallyFilledIn;
#end
Then, when it is initially filled in, just denote this boolean value.
ViewControllerOne *viewController = [[ViewControllerOne alloc] init];
[viewController setInitiallyFilledIn:YES];
Now, in viewDidAppear:, check this boolean value and check whether that method has been launched before. If it hasn't been launched before (to allow editing) and it is initially filled in, push the next controller!
#interface ViewControllerOne
#property (nonatomic, assign) BOOL hasCheckedFillInStatusBefore;
#end
#implementation ViewControllerOne
-(void)viewDidAppear:(BOOL)animated {
[super viewDidAppear:animated];
if ([self isInitiallyFilledIn] && ![self hasCheckedFillInStatusBefore]) {
// push the next view controller
}
[self setHasCheckedFillInStatusBefore:YES];
}
#end
Alternatively, if you want to display the two view controllers at the same time, you could alter the navigation stack:
// create instances of ViewControllerOne and ViewControllerTwo
NSMutableArray *viewControllers = [[[self navigationController] viewControllers] mutableCopy];
[viewControllers addObjectsFromArray:#[viewControllerOne, viewControllerTwo]];
[[self navigationController] setViewControllers:viewControllers animated:YES];
Note, the ViewControllerOne will not have viewDidLoad called so if you do any setup in that method (such as a back button title or the view controller title), you will either have to manually invoke that method before setting the view controllers or move that setup to the initializer.