How to be alerted when uiviewcontroller is pushed / popped from navigation stack

Question

I need to do certain things when my view controller is both pushed or popped from the navigation stack, but don't want to use viewillappear / viewdidappear or viewwilldisappear / viewdiddisappear since those cover cases besides when the view controller is pushed / popped. Is the correct way to go about this to use the navigationcontroller delegate and the navigationController:didShowViewController:animated: and navigationController:willShowViewController:animated: ? If not, how is the best way to go about this?

score 8 · Accepted Answer · edited May 23 '17 at 11:52

To find out when it's pushed, you can use the

UINavigationControllerDelegate

and implement

- (void)navigationController:(UINavigationController *)navigationController 
      willShowViewController:(UIViewController *)viewController
                    animated:(BOOL)animated

This method will fire whenever the viewcontroller is pushed into the navigation stack, and whenever the viewcontroller on top of it is popped off, thus revealing it again. So you have to use a flag to figure out if it's been initialized yet, if it hasn't means it just was pushed.

To find out when it's been popped, use this answer:

viewWillDisappear: Determine whether view controller is being popped or is showing a sub-view controller

score 6 · Answer 2 · answered Jan 11 '12 at 08:26

You can try UINavigationController delegate methods it calls when object push or pop from navigation controller stack.

- (void)navigationController:(UINavigationController *)navigationController willShowViewController:(UIViewController *)viewController animated:(BOOL)animated;
- (void)navigationController:(UINavigationController *)navigationController didShowViewController:(UIViewController *)viewController animated:(BOOL)animated;

score 3 · Answer 3 · edited Oct 09 '16 at 12:57

3

Here's an example to detect when a view controller is being pushed onto the navigation stack by overriding -viewWillAppear: and popped by overriding -viewWillDisappear:

-(void) viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
    if (self.isMovingToParentViewController) {
        NSLog(@"view controller being pushed");        
    }
}

-(void) viewWillDisappear:(BOOL)animated {
[super viewWillDisappear:animated];
    if (self.isMovingFromParentViewController) {
        NSLog(@"view controller being popped");
    }
}

edited Oct 09 '16 at 12:57

Cœur

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answered May 12 '15 at 00:56

MobileDev

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1

`Overriding` is a much better word. – 0xC0DED00D Mar 11 '16 at 23:16

Mike M · Answer 4 · 2014-09-23T15:10:19.733

You can always create a simple subclass of the UINavigationController and wrap its superclass's methods so that you set a flag before calling them:

ActionNavigationController.h

#import <UIKit/UIKit.h>

@interface ActionNavigationController : UINavigationController
@property (nonatomic, readonly) BOOL pushing;
@end

ActionNavigationController.m

#import "ActionNavigationController.h"

@implementation ActionNavigationController
@synthesize pushing = _pushing;

-(void)pushViewController:(UIViewController *)viewController 
                 animated:(BOOL)animated {
    _pushing = YES;
    [super pushViewController:viewController animated:animated];
}

- (UIViewController *)popViewControllerAnimated:(BOOL)animated {
    _pushing = NO;
    return [super popViewControllerAnimated:animated];
}
- (NSArray *)popToViewController:(UIViewController *)viewController 
                        animated:(BOOL)animated {
    _pushing = NO;
    return [super popToViewController:viewController animated:animated];
}
- (NSArray *)popToRootViewControllerAnimated:(BOOL)animated {
    _pushing = NO;
    return [super popToRootViewControllerAnimated:animated];
}

@end

As pushing will evaluate to NO event if nothing is happening, this code is expected to be accessed from the UINavigationControllerDelegate.

score 1 · Answer 5 · answered Dec 19 '17 at 02:31

Be careful to use

- (void)navigationController:(UINavigationController *)navigationController 
  willShowViewController:(UIViewController *)viewController
                animated:(BOOL)animated

If user swipe from edge into right for popping view controller(and not actually pop it), it will invoke above delegate's function but not below function

- (void)navigationController:(UINavigationController *)navigationController 
   didShowViewController:(UIViewController *)viewController 
                animated:(BOOL)animated;

Please refer to https://gist.github.com/nonamelive/9334458

score 0 · Answer 6 · answered Apr 03 '16 at 22:04

You can do something like that in willShowViewController

func navigationController(navigationController: UINavigationController, willShowViewController viewController: UIViewController, animated: Bool) {
    if self.navigationController!.viewControllers.contains(self){
        print ("push")
    } else {
        print ("pop")
    }
}

score 0 · Answer 7 · answered Sep 30 '19 at 06:48

(void)navigationController:(UINavigationController *)navigationController willShowViewController:(UIViewController *)viewController animated:(BOOL)animated;
(void)navigationController:(UINavigationController *)navigationController didShowViewController:(UIViewController *)viewController animated:(BOOL)animated;

these delegate functions arent invoked on iOS13 devices (compiled with Xcode 11). Is this a bug for now?

malhal · Answer 8 · 2019-10-07T12:47:14.447

0

It's bad practice to set the delegate to something inside the navigation controller's hierarchy, instead observe the notifications:

UINavigationControllerWillShowViewControllerNotification

UINavigationControllerDidShowViewControllerNotification

And the userInfo object contains the "NextVisible" and "LastVisible" view controllers. However using isMoving in appearance methods is probably the best way.

edited Oct 07 '19 at 12:47

answered Oct 05 '19 at 22:24

malhal

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How to be alerted when uiviewcontroller is pushed / popped from navigation stack

8 Answers8