Detecting when the back button is pressed on a navbar

Question

I need to perform some actions when the back button return to previous screen  return to parent-view  button is pressed on a Navbar   Is there some method I can implement to catch the event and fire off some actions to pause and save data before the screen disappears

User · Answer

Those who claim that this doesn t work are mistaken  override func viewWillDisappear   animated  Bool        super viewWillDisappear animated      if self isMovingFromParent           print  quot we are being popped quot            That works fine  So what is causing the widespread myth that it doesn   t  The problem seems to be due to an incorrect implementation of a different method  namely that the implementation of willMove toParent   forgot to call super  If you implement willMove toParent   without calling super  then self isMovingFromParent will be false and the use of viewWillDisappear will appear to fail  It didn t fail  you broke it  NOTE  The real problem is usually the second view controller detecting that the first view controller was popped  Please see also the more general discussion here  Unified UIViewController  quot became frontmost quot  detection  EDIT A comment suggests that this should be viewDidDisappear rather than viewWillDisappear

User · Answer

SWIFT   finaly found solution   method we were looking for is  willShowViewController  which is delegate method of UINavigationController    IMPORT UINavigationControllerDelegate    class PushedController  UIViewController  UINavigationControllerDelegate        override func viewDidLoad               set delegate to current class  self          navigationController  delegate   self            func navigationController navigationController  UINavigationController  willShowViewController viewController  UIViewController  animated  Bool              MyViewController shoud be the name of your parent Class         if var myViewController   viewController as  MyViewController                 YOUR STUFF

User · Answer

While viewWillAppear   and viewDidDisappear   are called when the back button is tapped  they are also called at other times  See end of answer for more on that   Using UIViewController parent  Detecting the back button is better done when the VC is removed from it s parent  the NavigationController  with the help of willMoveToParentViewController     OR didMoveToParentViewController    If parent is nil  the view controller is being popped off the navigation stack and dismissed  If parent is not nil  it is being added to the stack and presented       Objective-C - void willMoveToParentViewController  UIViewController   parent         super willMoveToParentViewController parent       if   parent             The back button was pressed or interactive gesture used              Swift override func willMove toParent parent  UIViewController         super willMove toParent  parent      if parent    nil              The back button was pressed or interactive gesture used           Swap out willMove for didMove and check self parent to do work after the view controller is dismissed   Stopping the dismiss  Do note  checking the parent doesn t allow you to  pause  the transition if you need to do some sort of async save  To do that you could implement the following  Only downside here is you lose the fancy iOS styled animated back button  Also be careful here with the interactive swipe gesture  Use the following to handle this case   var backButton   UIBarButtonItem   override func viewDidLoad         super viewDidLoad            Disable the swipe to make sure you get your chance to save      self navigationController  interactivePopGestureRecognizer enabled   false          Replace the default back button     self navigationItem setHidesBackButton true  animated  false      self backButton   UIBarButtonItem title   Back   style  UIBarButtonItemStyle Plain  target  self  action   goBack       self navigationItem leftBarButtonItem   backButton       Then handle the button selection func goBack            Here we just remove the back button  you could also disabled it or better yet show an activityIndicator     self navigationItem leftBarButtonItem   nil     someData saveInBackground    success  error  - gt  Void in         if success               self navigationController  popViewControllerAnimated true                 Don t forget to re-enable the interactive gesture             self navigationController  interactivePopGestureRecognizer enabled   true                   else               self navigationItem leftBarButtonItem   self backButton                Handle the error                       More on view will did appear  If you didn t get the viewWillAppear viewDidDisappear issue  Let s run through an example  Say you have three view controllers    ListVC  A table view of things DetailVC  Details about a thing SettingsVC  Some options for a thing   Lets follow the calls on the detailVC as you go from the listVC to settingsVC and back to listVC  List   Detail  push detailVC  Detail viewDidAppear  lt - appear Detail   Settings  push settingsVC  Detail viewDidDisappear  lt - disappear  And as we go back    Settings   Detail  pop settingsVC   Detail viewDidAppear  lt - appear Detail   List  pop detailVC  Detail viewDidDisappear  lt - disappear  Notice that viewDidDisappear is called multiple times  not only when going back  but also when going forward  For a quick operation that may be desired  but for a more complex operation like a network call to save  it may not

User · Answer

UPDATE  According to some comments  the solution in the original answer does not seem to work under certain scenarios in iOS 8   I can t verify that that is actually the case without further details   For those of you however in that situation there s an alternative  Detecting when a view controller is being popped is possible by overriding willMove toParentViewController    The basic idea is that a view controller is being popped when parent is nil   Check out  Implementing a Container View Controller  for further details     Since iOS 5 I ve found that the easiest way of dealing with this situation is using the new method -  BOOL isMovingFromParentViewController   -  void viewWillDisappear  BOOL animated      super viewWillDisappear animated      if  self isMovingFromParentViewController           Do your stuff here         -  BOOL isMovingFromParentViewController makes sense when you are pushing and popping controllers in a navigation stack   However  if you are presenting modal view controllers you should use -  BOOL isBeingDismissed instead   -  void viewWillDisappear  BOOL animated      super viewWillDisappear animated      if  self isBeingDismissed           Do your stuff here         As noted in this question  you could combine both properties   -  void viewWillDisappear  BOOL animated      super viewWillDisappear animated      if  self isMovingFromParentViewController    self isBeingDismissed           Do your stuff here         Other solutions rely on the existence of a UINavigationBar  Instead like my approach more because it decouples the required tasks to perform from the action that triggered the event  i e  pressing a back button

User · Answer

7ynk3r s answer was really close to what I did use in the end but it needed some tweaks   -  BOOL navigationBar  UINavigationBar   navigationBar shouldPopItem  UINavigationItem   item        UIViewController  topViewController   self topViewController      BOOL wasBackButtonClicked   topViewController navigationItem    item       if  wasBackButtonClicked            if   topViewController respondsToSelector  selector navBackButtonPressed                     if user did press back on the view controller where you handle the navBackButtonPressed              topViewController performSelector  selector navBackButtonPressed                return NO            else                  if user did press back but you are not on the view controller that can handle the navBackButtonPressed              self popViewControllerAnimated YES               return YES                  else              when you call popViewController programmatically you do not want to pop it twice         return YES

User · Answer

You can use the back button callback  like this   -  BOOL  navigationShouldPopOnBackButton        self backAction       return NO     -  void  backAction          your code goes here        show confirmation alert  for example                for swift version you can do something like in global scope  extension UIViewController         objc func navigationShouldPopOnBackButton   - gt  Bool        return true          extension UINavigationController  UINavigationBarDelegate        public func navigationBar   navigationBar  UINavigationBar  shouldPop item  UINavigationItem  - gt  Bool             return self topViewController  navigationShouldPopOnBackButton      true           Below one you put in the viewcontroller where you want to control back button action   override func navigationShouldPopOnBackButton   - gt  Bool       self backAction    Your action you want to perform       return true

User · Answer

I ve playing  or fighting  with this problem for two days  IMO the best approach is just to create an extension class and a protocol  like this     protocol UINavigationControllerBackButtonDelegate  lt NSObject gt         Indicates that the back button was pressed     If this message is implemented the pop logic must be manually handled      -  void backButtonPressed   end   interface UINavigationController BackButtonHandler   end   implementation UINavigationController BackButtonHandler  -  BOOL navigationBar  UINavigationBar   navigationBar shouldPopItem  UINavigationItem   item       UIViewController  topViewController   self topViewController      BOOL wasBackButtonClicked   topViewController navigationItem    item      SEL backButtonPressedSel    selector backButtonPressed       if  wasBackButtonClicked  amp  amp   topViewController respondsToSelector backButtonPressedSel              topViewController performSelector backButtonPressedSel           return NO            else            self popViewControllerAnimated YES           return YES           end   This works because UINavigationController will receive a call to navigationBar shouldPopItem  every time a view controller is popped  There we detect if back was pressed or not  any other button   The only thing you have to do is implement the protocol in the view controller where back is pressed    Remember to manually pop the view controller inside backButtonPressedSel  if everything is ok   If you already have subclassed UINavigationViewController and implemented navigationBar shouldPopItem  don t worry  this won t interfere with it   You may also be interested in disable the back gesture   if   self navigationController respondsToSelector  selector interactivePopGestureRecognizer          self navigationController interactivePopGestureRecognizer enabled   NO

User · Answer

As purrrminator says  the answer by elitalon is not completely right  since your stuff would be executed even when popping the controller programmatically   The solution I have found so far is not very nice  but it works for me  Besides what elitalon said  I also check whether I m popping programmatically or not   -  void viewWillDisappear  BOOL animated      super viewWillDisappear animated      if   self isMovingFromParentViewController    self isBeingDismissed         amp  amp   self isPoppingProgrammatically           Do your stuff here         You have to add that property to your controller and set it to YES before popping programmatically   self isPoppingProgrammatically   YES   self navigationController popViewControllerAnimated YES     Thanks for your help

User · Answer

For the record  I think this is more of what he was looking for         UIBarButtonItem  l backButton     UIBarButtonItem alloc  initWithBarButtonSystemItem UIBarButtonSystemItemRewind target self action  selector backToRootView          self navigationItem leftBarButtonItem   l backButton        -  void  backToRootView  id sender               Perform some custom code           self navigationController popToRootViewControllerAnimated YES

User · Answer

self navigationController isMovingFromParentViewController is not working anymore on iOS8 and 9 I use    - void  viewWillDisappear  BOOL animated        super viewWillDisappear animated       if  self navigationController topViewController    self                   Is Popping

User · Answer

I have solved this problem by adding a UIControl to the navigationBar on the left side    UIControl  leftBarItemControl     UIControl alloc  initWithFrame CGRectMake 0  0  90  44     leftBarItemControl addTarget self action  selector onLeftItemClick   forControlEvents UIControlEventTouchUpInside   self leftItemControl   leftBarItemControl   self navigationController navigationBar addSubview leftBarItemControl    self navigationController navigationBar bringSubviewToFront leftBarItemControl     And you need to remember to remove it when view will disappear   -  void  viewWillDisappear  BOOL animated        super viewWillDisappear animated       if  self leftItemControl             self leftItemControl removeFromSuperview                 That s all

User · Answer

For Swift with a UINavigationController   override func viewWillDisappear animated  Bool        super viewWillDisappear animated      if self navigationController  topViewController    self           print  back button tapped

User · Answer

First Method  -  void didMoveToParentViewController  UIViewController   parent       if    parent isEqual self parentViewController              NSLog   Back pressed              Second Method  - void  viewWillDisappear  BOOL animated       if   self navigationController viewControllers indexOfObject self   NSNotFound              back button was pressed   We know this is true because self is no longer           in the navigation stack               super viewWillDisappear animated

User · Answer

The best way is to use the UINavigationController delegate methods  -  void navigationController  UINavigationController   navigationController willShowViewController  UIViewController   viewController animated  BOOL animated   Using this you can know what controller is showing the UINavigationController   if   viewController isKindOfClass  HomeController class          NSLog   Show home controller

User · Answer

You should check out the UINavigationBarDelegate Protocol  In this case you might want to use the navigationBar shouldPopItem  method

User · Answer

As Coli88 said  you should check the UINavigationBarDelegate protocol    In a more general way  you can also use the -  void viewWillDisapear  BOOL animated to perform custom work when the view retained by the currently visible view controller is about to disappear  Unfortunately  this would cover bother the push and the pop cases

User · Answer

This works for me in iOS 9 3 x with Swift   override func didMoveToParentViewController parent  UIViewController         super didMoveToParentViewController parent       if parent    self navigationController  parentViewController           print  Back tapped             Unlike other solutions here  this doesn t seem to trigger unexpectedly

[iphone] Detecting when the 'back' button is pressed on a navbar

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