CATransition also animating the navigationBar

Question

I want to make a custom animation to pop my navigation controller. I only want to animate the view, not the navigationBar. With this code I animate both, the view and the navigationBar. How can I only animate the view??

CATransition* transition = [CATransition animation];
transition.duration = 0.3;
transition.type = kCATransitionFade;
transition.subtype = kCATransitionFromTop;

[self.navigationController.view.layer addAnimation:transition forKey:kCATransition];
[self.navigationController popViewControllerAnimated:NO];

this code is fired when a custom back button added inside the navigationcontroller bar is pressed.

Answer 1

Here is a code that does custom animation both for back button and when you call popRootViewController: method.

It's a class that extends UINavigationViewController which by itself contradicts Apple's docs also it assigns private variable using KVO, which might stop working as soon as engineers change UINavigationController class so use it a t your own risk.

#import "MyNavigationController.h"

@interface MyNavigationController () <UINavigationBarDelegate> {
    // Flag that we will use to avoid collisions between navgiation bar
    // when we call popViewControllerAnimated: method directly
    BOOL _isPopping;
}
- (UIViewController *)myPopViewControllerAniamted:(BOOL)animated;
@end

@implementation MyNavigationController

- (id)init
{
    self = [super init];
    if (!self) return nil;
    // We can't intercept delegation of the original navigation bar,
    // we have to replace it with our own, by assigning new instance to
    // the private _navigationBar vairable
    UINavigationBar *navigationBar = [[UINavigationBar alloc] init];
    navigationBar.delegate = self;
    [self setValue:navigationBar forKey:@"_navigationBar"];

    return self;
}

// This is the delegate method called when you're about to pop navigation item
- (BOOL)navigationBar:(UINavigationBar *)navigationBar shouldPopItem:(UINavigationItem *)item
{
// If we're in the process of popping items we don't want to reenter
    if (!_isPopping) {
        [self myPopViewControllerAniamted:YES];
    }
    return YES;
}

// Similarly we have to override popToRootViewControllerAnimated:
// The only difference would be that we use not previous view as a
// target for the transfition, but the very first view
- (UIViewController *)popViewControllerAnimated:(BOOL)animated
{
    return [self myPopViewControllerAniamted:animated];
}

// Our custom popping method
- (UIViewController *)myPopViewControllerAniamted:(BOOL)animated
{
    _isPopping = YES;
    // If we got here, we have at least two view controllers in the stack
    UIViewController *currentViewController = self.topViewController;
    if (animated && self.viewControllers.count > 1) {
        UIView *currentView = currentViewController.view;
        UIViewController *previousViewController = [self.viewControllers objectAtIndex:self.viewControllers.count - 2];
        UIView *previousView = previousViewController.view;
        previousView.alpha = 0.0;
        [currentView.superview insertSubview:previousView belowSubview:currentView];
        // I use UIView just for the sake of the simplicity of this example
        // In case of core animation you will have to deal with delegates
        // to trigger view controller popping when animation finishes
        [UIView animateWithDuration:0.33 delay:0.0 options:UIViewAnimationOptionCurveEaseInOut animations:^{
            currentView.alpha = 0.0;
            previousView.alpha = 1.0;
        } completion:^(BOOL finished) {
            [super popViewControllerAnimated:NO];
            _isPopping = NO;
        }];
    } else {
        [super popViewControllerAnimated:NO];
        _isPopping = NO;
    }
    return currentViewController;
}

@end

Once again, it was done purely as exercise of what is possible, I would highly recommend reading UIViewController guide, probably Container View Controller can satisfy you needs as a designated way of customizing view controller behaviour.

Hope it helps!