Setting action for back button in navigation controller

Question

I m trying to overwrite the default action of the back button in a navigation controller  I ve provided a target an action on the custom button   The odd thing is when assigning it though the backbutton attribute it doesn t pay attention to them and it just pops the current view and goes back to the root   UIBarButtonItem  backButton     UIBarButtonItem alloc                                     initWithTitle    Servers                                     style UIBarButtonItemStylePlain                                    target self                                    action  selector home    self navigationItem backBarButtonItem   backButton    As soon as I set it through the leftBarButtonItem on the navigationItem it calls my action  however then the button looks like a plain round one instead of the arrowed back one   self navigationItem leftBarButtonItem   backButton    How can I get it to call my custom action before going back to the root view   Is there a way to overwrite the default back action  or is there a method that is always called when leaving a view  viewDidUnload doesn t do that

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Swift version of  onegray s answer  protocol RequestsNavigationPopVerification       var confirmationTitle  String   get       var confirmationMessage  String   get      extension RequestsNavigationPopVerification where Self  UIViewController       var confirmationTitle  String           return  Go back              var confirmationMessage  String           return  Are you sure            final class NavigationController  UINavigationController        func navigationBar navigationBar  UINavigationBar  shouldPopItem item  UINavigationItem  - gt  Bool            guard let requestsPopConfirm   topViewController as  RequestsNavigationPopVerification else               popViewControllerAnimated true              return true                    let alertController   UIAlertController title  requestsPopConfirm confirmationTitle  message  requestsPopConfirm confirmationMessage  preferredStyle   Alert           alertController addAction UIAlertAction title   Cancel   style   Cancel      in             dispatch async dispatch get main queue                      let dimmed   navigationBar subviews flatMap    0 alpha  lt  1    0   nil                   UIView animateWithDuration 0 25                        dimmed forEach    0 alpha   1                                                return                     alertController addAction UIAlertAction title   Go back   style   Default      in             dispatch async dispatch get main queue                      self popViewControllerAnimated true                                     presentViewController alertController  animated  true  completion  nil           return false           Now in any controller  just conform to RequestsNavigationPopVerification and this behaviour is adopted by default

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onegray s solution is not safe According to the official documents by Apple https   developer apple com library ios documentation Cocoa Conceptual ProgrammingWithObjectiveC CustomizingExistingClasses CustomizingExistingClasses html  we should avoid doing that    If the name of a method declared in a category is the same as a method in the original class  or a method in another category on the same class  or even a superclass   the behavior is undefined as to which method implementation is used at runtime  This is less likely to be an issue if you   re using categories with your own classes  but can cause problems when using categories to add methods to standard Cocoa or Cocoa Touch classes

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Try putting this into the view controller where you want to detect the press   - 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

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By using the target and action variables that you are currently leaving  nil   you should be able to wire your save-dialogs in so that they are called when the button is  selected   Watch out  this may get triggered at strange moments   I agree mostly with Amagrammer  but I don t think it would be that hard to make the button with the arrow custom  I would just rename the back button  take a screen shot  photoshop the button size needed  and have that be the image on the top of your button

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Found new way to do it    Objective-C  -  void didMoveToParentViewController  UIViewController   parent      if  parent    NULL            NSLog   Back Pressed              Swift  override func didMoveToParentViewController parent  UIViewController         if parent    nil           println  Back Pressed

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The answer from  William is correct however  if the user starts a swipe-to-go-back gesture the viewWillDisappear method is called and even self won t be in the navigation stack  that is  self navigationController viewControllers won t contain self   even if the swipe is not completed and the view controller is not actually popped  Thus  the solution would be to    Disable the swipe-to-go-back gesture in viewDidAppear and only allow using the back button  by using   if   self navigationController respondsToSelector  selector interactivePopGestureRecognizer          self navigationController interactivePopGestureRecognizer enabled   NO     Or simply use viewDidDisappear instead  as follows   -  void viewDidDisappear  BOOL animated        super viewDidDisappear animated       if    self navigationController viewControllers containsObject self                    back button was pressed or the the swipe-to-go-back gesture was            completed  We know this is true because self is no longer            in the navigation stack

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For a form that requires user input like this  I would recommend invoking it as a  modal  instead of part of your navigation stack  That way they have to take care of business on the form  then you can validate it and dismiss it using a custom button  You can even design a nav bar that looks the same as the rest of your app but gives you more control

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Easiest way   You can use the UINavigationController s delegate methods  The method willShowViewController is called when the back button of your VC is pressed do whatever you want when back btn pressed  -  void navigationController  UINavigationController   navigationController willShowViewController  UIViewController   viewController animated  BOOL animated

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You can try accessing the NavigationBars Right Button item and set its selector property   heres a reference UIBarButtonItem reference  another thing if this doenst work that will def work is  set the right button item of the nav bar to a custom UIBarButtonItem that you create and set its selector   hope this helps

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Unlike Amagrammer said  it s possible  You have to subclass your navigationController  I explained everything here  including example code

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It isn t possible to do directly  There are a couple alternatives    Create your own custom UIBarButtonItem that validates on tap and pops if the test passes Validate the form field contents using a UITextField delegate method  such as -textFieldShouldReturn   which is called after the Return or Done button is pressed on the keyboard   The downside of the first option is that the left-pointing-arrow style of the back button cannot be accessed from a custom bar button  So you have to use an image or go with a regular style button   The second option is nice because you get the text field back in the delegate method  so you can target your validation logic to the specific text field sent to the delegate call-back method

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Swift Version    of https   stackoverflow com a 19132881 826435   In your view controller you just conform to a protocol and perform whatever action you need   extension MyViewController  NavigationControllerBackButtonDelegate       func shouldPopOnBackButtonPress   - gt  Bool           performSomeActionOnThePressOfABackButton           return false           Then create a class  say NavigationController BackButton  and just copy-paste the code below   protocol NavigationControllerBackButtonDelegate       func shouldPopOnBackButtonPress   - gt  Bool    extension UINavigationController       public func navigationBar   navigationBar  UINavigationBar  shouldPop item  UINavigationItem  - gt  Bool              Prevents from a synchronization issue of popping too many navigation items            and not enough view controllers or viceversa from unusual tapping         if viewControllers count  lt  navigationBar items  count               return true                       Check if we have a view controller that wants to respond to being popped         var shouldPop   true         if let viewController   topViewController as  NavigationControllerBackButtonDelegate               shouldPop   viewController shouldPopOnBackButtonPress                      if  shouldPop                DispatchQueue main async                   self popViewController animated  true                          else                  Prevent the back button from staying in an disabled state             for view in navigationBar subviews                   if view alpha  lt  1 0                       UIView animate withDuration  0 25  animations                            view alpha   1 0                                                                            return false

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This approach worked for me  but the  Back  button will not have the   lt   sign    -  void viewDidLoad        super viewDidLoad        UIBarButtonItem  backNavButton     UIBarButtonItem alloc  initWithTitle   Back                                                                        style UIBarButtonItemStyleBordered                                                                      target self                                                                      action  selector backButtonClicked        self navigationItem leftBarButtonItem   backNavButton     - void backButtonClicked          Do something        AppDelegate  delegate    AppDelegate    UIApplication sharedApplication  delegate        delegate navController popViewControllerAnimated YES

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I ve implemented UIViewController-BackButtonHandler extension  It does not need to subclass anything  just put it into your project and override navigationShouldPopOnBackButton method in UIViewController class   - BOOL  navigationShouldPopOnBackButton       if needsShowConfirmation               Show confirmation alert                        return NO     Ignore  Back  button this time           return YES     Process  Back  button click and Pop view controler     Download sample app

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Here s my Swift solution  In your subclass of UIViewController  override the navigationShouldPopOnBackButton method    extension UIViewController       func navigationShouldPopOnBackButton   - gt  Bool           return true          extension UINavigationController        func navigationBar navigationBar  UINavigationBar  shouldPopItem item  UINavigationItem  - gt  Bool           if let vc   self topViewController               if vc navigationShouldPopOnBackButton                     self popViewControllerAnimated true                else                   for it in navigationBar subviews                       let view   it as  UIView                     if view alpha  lt  1 0                            UIView  animateWithDuration 0 25  animations       - gt  Void in                             view alpha   1 0                                                                                     return false                                 return true

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Found a solution which retains the back button style as well  Add the following method to your view controller   - void  overrideBack       UIButton  transparentButton     UIButton alloc  init        transparentButton setFrame CGRectMake 0 0  50  40         transparentButton setBackgroundColor  UIColor clearColor         transparentButton addTarget self action  selector backAction   forControlEvents UIControlEventTouchUpInside        self navigationController navigationBar addSubview transparentButton         Now provide a functionality as needed in the following method   - void backAction  UIBarButtonItem   sender         Your functionality     All it does is to cover the back button with a transparent button

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Using Swift   override func viewWillDisappear animated  Bool        super viewWillDisappear animated      if self navigationController  topViewController    self           print  back button tapped

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The solution I have found so far is not very nice  but it works for me  Taking this answer  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

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At least in Xcode 5  there is a simple and pretty good  not perfect  solution   In IB  drag a Bar Button Item off the Utilities pane and drop it on the left side of the Navigation Bar where the Back button would be  Set the label to  Back    You will have a functioning button that you can tie to your IBAction and close your viewController   I m doing some work and then triggering an unwind segue and it works perfectly   What isn t ideal is that this button does not get the  lt  arrow and does not carry forward the previous VCs title  but I think this can be managed   For my purposes  I set the new Back button to be a  Done  button so it s purpose is clear   You also end up with two Back buttons in the IB navigator  but it is easy enough to label it for clarity

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Overriding navigationBar   navigationBar shouldPop   This is not a good idea  even if it works  for me it generated random crashes on navigating back  I advise you to just override the back button by removing the default backButton from navigationItem and creating a custom back button like below   override func viewDidLoad       super viewDidLoad          navigationItem leftBarButton    init title   quot Go Back quot         action   selector myCutsomBackAction                                                         Building on previous responses with UIAlert in Swift5 in a Asynchronous way  protocol NavigationControllerBackButtonDelegate       func shouldPopOnBackButtonPress   completion   escaping  Bool  - gt         extension UINavigationController  UINavigationBarDelegate       public func navigationBar   navigationBar  UINavigationBar  shouldPop item  UINavigationItem  - gt  Bool                  if viewControllers count  lt  navigationBar items  count               return true                               Check if we have a view controller that wants to respond to being popped                  if let viewController   topViewController as  NavigationControllerBackButtonDelegate                            viewController shouldPopOnBackButtonPress   shouldPop in                 if  shouldPop                            on confirm   gt  pop                     DispatchQueue main async                           self popViewController animated  true                                          else                           on cancel   gt  do nothing                                                 return false   gt  so navigator will cancel the popBack                 until user confirm or cancel             return false          else              DispatchQueue main async                   self popViewController animated  true                                  return true            On your controller  extension MyController  NavigationControllerBackButtonDelegate            func shouldPopOnBackButtonPress   completion   escaping  Bool  - gt                     let msg    quot message quot                       show UIAlert         alertAttention msg  msg  actions                              init title   quot Continuer quot   style   destructive  handler      in                 completion true                               init title   quot Annuler quot   style   cancel  handler      in                 completion false

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To intercept the Back button  simply cover it with a transparent UIControl and intercept the touches    interface MyViewController   UIViewController       UIControl    backCover      BOOL        inhibitBackButtonBOOL     end   implementation MyViewController - void viewDidAppear  BOOL animated        super viewDidAppear animated           Cover the back button  cannot do this in viewWillAppear -- too soon      if   backCover    nil             backCover     UIControl alloc  initWithFrame CGRectMake  0  0  80  44     if TARGET IPHONE SIMULATOR            show the cover for testing         backCover backgroundColor    UIColor colorWithRed 1 0 green 0 0 blue 0 0 alpha 0 15    endif          backCover addTarget self action  selector backCoverAction  forControlEvents UIControlEventTouchDown           UINavigationBar  navBar   self navigationController navigationBar           navBar addSubview backCover            - void viewWillDisappear  BOOL animated        super viewWillDisappear animated         backCover removeFromSuperview       backCover   nil     -  void backCoverAction       if   inhibitBackButtonBOOL             NSLog   Back button aborted               notify the user why          else            self navigationController popViewControllerAnimated YES       Back           end

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Use isMovingFromParentViewController  override func viewWillDisappear animated  Bool        super viewWillDisappear true       if self isMovingFromParentViewController              current viewController is removed from parent            do some work

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Swift  override func viewWillDisappear animated  Bool        let viewControllers   self navigationController  viewControllers      if indexOfArray viewControllers   searchObject  self     nil              do something           super viewWillDisappear animated     func indexOfArray array  AnyObject   searchObject  AnyObject - gt  Int        for  index  value  in enumerate array            if value as UIViewController    searchObject as UIViewController               return index                     return nil

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I don t believe this is possible  easily  The only way I believe to get around this is to make your own back button arrow image to place up there  It was frustrating for me at first but I see why  for consistency s sake  it was left out    You can get close  without the arrow  by creating a regular button and hiding the default back button   self navigationItem leftBarButtonItem      UIBarButtonItem alloc  initWithTitle   Servers  style UIBarButtonItemStyleDone target nil action nil  autorelease   self navigationItem hidesBackButton   YES

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There s an easier way by just subclassing the delegate method of the UINavigationBar and override the ShouldPopItemmethod

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This technique allows you to change the text of the  back  button without affecting the title of any of the view controllers or seeing the back button text change during the animation   Add this to the init method in the calling view controller   UIBarButtonItem  temporaryBarButtonItem     UIBarButtonItem alloc  init      temporaryBarButtonItem title     Back   self navigationItem backBarButtonItem   temporaryBarButtonItem   temporaryBarButtonItem release

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Swift 4 iOS 11 3 Version  This builds on the answer from kgaidis from https   stackoverflow com a 34343418 4316579 I am not sure when the extension stopped working  but at the time of this writing  Swift 4   it appears that the extension will no longer be executed unless you declare UINavigationBarDelegate conformity as described below  Hope this helps people that are wondering why their extension no longer works  extension UINavigationController  UINavigationBarDelegate       public func navigationBar   navigationBar  UINavigationBar  shouldPop item  UINavigationItem  - gt  Bool

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For some threading reasons  the solution mentionned by  HansPinckaers wasn t right for me  but I found a very easier way to catch a touch on the back button  and I wanna pin this down here in case this could avoid hours of deceptions for someone else  The trick is really easy   just add a transparent UIButton as a subview to your UINavigationBar  and set your selectors for him as if it was the real button  Here s an example using Monotouch and C   but the translation to objective-c shouldn t be too hard to find   public class Test   UIViewController       public override void ViewDidLoad             UIButton b   new UIButton new RectangleF 0  0  60  44      width must be adapted to label contained in button         b BackgroundColor   UIColor Clear    making the background invisible         b Title   string Empty     and no need to write anything         b TouchDown    delegate               Console WriteLine  caught                 if  true     check what you want here                 NavigationController PopViewControllerAnimated true      and then we pop if we want                    NavigationController NavigationBar AddSubview button      insert the button to the nav bar           Fun fact   for testing purposes and to find good dimensions for my fake button  I set its background color to blue    And it shows behind the back button  Anyway  it still catches any touch targetting the original button

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Here is Swift 3 version of  oneway s answer for catching navigation bar back button event before it gets fired  As UINavigationBarDelegate cannot be used for UIViewController  you need to create a delegate that will be triggered when navigationBar shouldPop is called    objc public protocol BackButtonDelegate          objc optional func navigationShouldPopOnBackButton   - gt  Bool     extension UINavigationController  UINavigationBarDelegate         public func navigationBar   navigationBar  UINavigationBar  shouldPop item  UINavigationItem  - gt  Bool            if viewControllers count  lt   navigationBar items  count                                 return true                    var shouldPop   true         let vc   self topViewController          if vc responds to   selector vc navigationShouldPopOnBackButton                 shouldPop   vc navigationShouldPopOnBackButton                      if shouldPop               DispatchQueue main async                   self popViewController animated  true                          else               for subView in navigationBar subviews                   if 0  lt  subView alpha  amp  amp  subView alpha  lt  1                        UIView animate withDuration  0 25  animations                            subView alpha   1                                                                           return false           And then  in your view controller add the delegate function   class BaseVC  UIViewController  BackButtonDelegate       func navigationShouldPopOnBackButton   - gt  Bool           if                   return true           else               return false                             I ve realised that we often want to add an alert controller for users to decide whether they wanna go back  If so  you can always return false in navigationShouldPopOnBackButton   function and close your view controller by doing something like this   func navigationShouldPopOnBackButton   - gt  Bool        let alert   UIAlertController title   Warning                                             message   Do you want to quit                                              preferredStyle   alert              alert addAction UIAlertAction title   Yes   style   default  handler    UIAlertAction in self yes                  alert addAction UIAlertAction title   No   style   cancel  handler    UIAlertAction in self no                  present alert  animated  true  completion  nil        return false    func yes          print  yes        DispatchQueue main async                   self navigationController  popViewController animated  true               func no         print  no

[ios] Setting action for back button in navigation controller

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