modal View controllers - how to display and dismiss

Question

I m breaking my head for the last one week on how to solve the issue with showing and dismissing multiple view controllers  I have created a sample project and pasting the code directly from the project  I have 3 view controllers with their corresponding  xib files  MainViewController  VC1 and VC2  I have two buttons on the main view controller   -  IBAction VC1Pressed  UIButton   sender       VC1  vc1     VC1 alloc  initWithNibName   VC1  bundle nil        vc1 setModalTransitionStyle UIModalTransitionStyleFlipHorizontal        self presentViewController vc1 animated YES completion nil       This opens VC1 with no issues  In VC1  I have another button that should open VC2 while at the same time dismiss VC1   -  IBAction buttonPressedFromVC1  UIButton   sender       VC2  vc2     VC2 alloc  initWithNibName   VC2  bundle nil        vc2 setModalTransitionStyle UIModalTransitionStyleFlipHorizontal        self presentViewController vc2 animated YES completion nil        self dismissViewControllerAnimated YES completion nil        This shows a warning  Attempt to dismiss from view controller  lt VC1  0x715e460 gt  while a presentation or dismiss is in progress    -  IBAction buttonPressedFromVC2  UIButton   sender        self dismissViewControllerAnimated YES completion nil        This is going back to VC1     I want it go back to the main view controller while at the same time VC1 should have been removed from memory for good  VC1 should only show up when I click on the VC1 button on the main controller   The other button on the Main view controller should also be able to display VC2 directly bypassing VC1 and should come back to the main controller when a button is clicked on VC2  There is no long running code  loops or any timers  Just bare bone calls to view controllers

User · Answer

I have solved the issue by using UINavigationController when presenting. In MainVC, when presenting VC1

let vc1 = VC1()
let navigationVC = UINavigationController(rootViewController: vc1)
self.present(navigationVC, animated: true, completion: nil)

In VC1, when I would like to show VC2 and dismiss VC1 in same time (just one animation), I can have a push animation by

let vc2 = VC2()
self.navigationController?.setViewControllers([vc2], animated: true)

And in VC2, when close the view controller, as usual we can use:

self.dismiss(animated: true, completion: nil)

User · Answer

This line   self dismissViewControllerAnimated YES completion nil    isn t sending a message to itself  it s actually sending a message to its presenting VC  asking it to do the dismissing  When you present a VC  you create a relationship between the presenting VC and the presented one  So you should not destroy the presenting VC while it is presenting  the presented VC can t send that dismiss message back      As you re not really taking account of it you are leaving the app in a confused state  See my answer Dismissing a Presented View Controller in which I recommend this method is more clearly written   self presentingViewController dismissViewControllerAnimated YES completion nil    In your case  you need to ensure that all of the controlling is done in mainVC   You should use a delegate to send the correct message back to MainViewController from ViewController1  so that mainVC can dismiss VC1 and then present VC2  In VC2 VC1 add a protocol in your  h file above the  interface   protocol ViewController1Protocol  lt NSObject gt       -  void dismissAndPresentVC2    end  and lower down in the same file in the  interface section declare a property to hold the delegate pointer   property  nonatomic weak  id  lt ViewController1Protocol gt  delegate   In the VC1  m file  the dismiss button method should call the delegate method -  IBAction buttonPressedFromVC1  UIButton   sender        self delegate dissmissAndPresentVC2     Now in mainVC  set it as VC1 s delegate when creating VC1  -  IBAction present1  id sender       ViewController1  vc     ViewController1 alloc  initWithNibName   quot ViewController1 quot  bundle nil       vc delegate   self       self present vc      and implement the delegate method  -  void dismissAndPresent2        self dismissViewControllerAnimated NO completion             self present2 nil              present2  can be the same method as  your VC2Pressed  button IBAction method  Note that it is called from the completion block to ensure that VC2 is not presented until VC1 is fully dismissed  You are now moving from VC1- gt VCMain- gt VC2 so you will probably want only one of the transitions to be animated  update In your comments you express surprise at the complexity required to achieve a seemingly simple thing  I assure you  this delegation pattern is so central to much of Objective-C and Cocoa  and this example is about the most simple you can get  that you really should make the effort to get comfortable with it  In Apple s View Controller Programming Guide they have this to say   Dismissing a Presented View Controller When it comes time to dismiss a presented view controller  the preferred approach is to let the presenting view controller dismiss it  In other words  whenever possible  the same view controller that presented the view controller should also take responsibility for dismissing it  Although there are several techniques for notifying the presenting view controller that its presented view controller should be dismissed  the preferred technique is delegation  For more information  see    Using Delegation to Communicate with Other Controllers      If you really think through what you want to achieve  and how you are going about it  you will realise that messaging your MainViewController to do all of the work is the only logical way out given that you don t want to use a NavigationController  If you do use a NavController  in effect you are  delegating   even if not explicitly  to the navController to do all of the work  There needs to be some object that keeps a central track of what s going on with your VC navigation  and you need some method of communicating with it  whatever you do  In practice Apple s advice is a little extreme    in normal cases  you don t need to make a dedicated delegate and method  you can rely on  self presentingViewController  dismissViewControllerAnimated  - it s when in cases like yours that you want your dismissing to have other effects on remote objects that you need to take care  Here is something you could imagine to work without all the delegate hassle    -  IBAction dismiss  id sender         self presentingViewController  dismissViewControllerAnimated YES                                                          completion             self presentingViewController performSelector  selector presentVC2                                                withObject nil               After asking the presenting controller to dismiss us  we have a completion block which calls a method in the presentingViewController to invoke VC2  No delegate needed   A big selling point of blocks is that they reduce the need for delegates in these circumstances   However in this case there are a few things getting in the way     in VC1 you don t know that mainVC implements the method present2 - you can end up with difficult-to-debug errors or crashes  Delegates help you to avoid this  once VC1 is dismissed  it s not really around to execute the completion block    or is it  Does self presentingViewController mean anything any more  You don t know  neither do I     with a delegate  you don t have this uncertainty  When I try to run this method  it just hangs with no warning or errors   So please    take the time to learn delegation  update2 In your comment you have managed to make it work by using this in VC2 s dismiss button handler    self view window rootViewController dismissViewControllerAnimated YES completion nil     This is certainly much simpler  but it leaves you with a number of issues  Tight coupling You are hard-wiring your viewController structure together  For example  if you were to insert a new viewController before mainVC  your required behaviour would break  you would navigate to the prior one   In VC1 you have also had to  import VC2  Therefore you have quite a lot of inter-dependencies  which breaks OOP MVC objectives  Using delegates  neither VC1 nor VC2 need to know anything about mainVC or it s antecedents so we keep everything loosely-coupled and modular  Memory VC1 has not gone away  you still hold two pointers to it   mainVC s presentedViewController property VC2 s presentingViewController property  You can test this by logging  and also just by doing this from VC2  self dismissViewControllerAnimated YES completion nil     It still works  still gets you back to VC1  That seems to me like a memory leak  The clue to this is in the warning you are getting here   self presentViewController vc2 animated YES completion nil    self dismissViewControllerAnimated YES completion nil       Attempt to dismiss from view controller  lt VC1  0x715e460 gt      while a presentation or dismiss is in progress   The logic breaks down  as you are attempting to dismiss the presenting VC of which VC2 is the presented VC  The second message doesn t really get executed - well perhaps some stuff happens  but you are still left with two pointers to an object you thought you had got rid of   edit - I ve checked this and it s not so bad  both objects do go away when you get back to mainVC  That s a rather long-winded way of saying - please  use delegates  If it helps  I made another brief description of the pattern here  Is passing a controller in a construtor always a bad practice  update 3 If you really want to avoid delegates  this could be the best way out  In VC1   self presentViewController VC2                    animated YES                  completion nil    But don t dismiss anything    as we ascertained  it doesn t really happen anyway  In VC2   self presentingViewController presentingViewController      dismissViewControllerAnimated YES                        completion nil    As we  know  we haven t dismissed VC1  we can reach back through VC1 to MainVC  MainVC dismisses VC1  Because VC1 has gone  it s presented VC2 goes with it  so you are back at MainVC in a clean state  It s still highly coupled  as VC1 needs to know about VC2  and VC2 needs to know that it was arrived at via MainVC- gt VC1  but it s the best you re going to get without a bit of explicit delegation

User · Answer

I wanted this   MapVC is a Map in full screen    When I press a button  it opens PopupVC  not in full screen  above the map   When I press a button in PopupVC  it returns to MapVC  and then I want to execute viewDidAppear   I did this   MapVC m  in the button action  a segue programmatically  and set delegate  -  void  buttonMapAction     PopupVC  popvc    self storyboard instantiateViewControllerWithIdentifier   popup       popvc delegate   self      self presentViewController popvc animated YES completion nil      -  void dismissAndPresentMap      self dismissViewControllerAnimated NO completion        NSLog   dismissAndPresentMap          When returns of the other view I call viewDidAppear but you can call to other functions      self viewDidAppear YES             PopupVC h  before  interface  add the protocol   protocol PopupVCProtocol  lt NSObject gt  -  void dismissAndPresentMap   end   after  interface  a new property   property  nonatomic weak  id  lt PopupVCProtocol gt  delegate    PopupVC m    -  void  buttonPopupAction      jump to dismissAndPresentMap on Map view    self delegate dismissAndPresentMap

User · Answer

Example in Swift   picturing the foundry s explanation above and the Apple s documentation    Basing on the Apple s documentation and the foundry s explanation above  correcting some errors   presentViewController version using delegate design pattern    ViewController swift  import UIKit  protocol ViewControllerProtocol       func dismissViewController1AndPresentViewController2      class ViewController  UIViewController  ViewControllerProtocol         IBAction func goToViewController1BtnPressed sender  UIButton            let vc1  ViewController1   self storyboard  instantiateViewControllerWithIdentifier  VC1   as ViewController1         vc1 delegate   self         vc1 modalTransitionStyle   UIModalTransitionStyle FlipHorizontal         self presentViewController vc1  animated  true  completion  nil             func dismissViewController1AndPresentViewController2             self dismissViewControllerAnimated false  completion       - gt  Void in             let vc2  ViewController2   self storyboard  instantiateViewControllerWithIdentifier  VC2   as ViewController2             self presentViewController vc2  animated  true  completion  nil                        ViewController1 swift  import UIKit  class ViewController1  UIViewController        var delegate  protocol lt ViewControllerProtocol gt         IBAction func goToViewController2 sender  UIButton            self delegate dismissViewController1AndPresentViewController2              ViewController2 swift  import UIKit  class ViewController2  UIViewController         Basing on the foundry s explanation above  correcting some errors   pushViewController version using delegate design pattern    ViewController swift  import UIKit  protocol ViewControllerProtocol       func popViewController1AndPushViewController2      class ViewController  UIViewController  ViewControllerProtocol         IBAction func goToViewController1BtnPressed sender  UIButton            let vc1  ViewController1   self storyboard  instantiateViewControllerWithIdentifier  VC1   as ViewController1         vc1 delegate   self         self navigationController  pushViewController vc1  animated  true             func popViewController1AndPushViewController2             self navigationController  popViewControllerAnimated false          let vc2  ViewController2   self storyboard  instantiateViewControllerWithIdentifier  VC2   as ViewController2         self navigationController  pushViewController vc2  animated  true             ViewController1 swift  import UIKit  class ViewController1  UIViewController        var delegate  protocol lt ViewControllerProtocol gt         IBAction func goToViewController2 sender  UIButton            self delegate popViewController1AndPushViewController2              ViewController2 swift  import UIKit  class ViewController2  UIViewController

User · Answer

Radu Simionescu - awesome work  and below Your solution for Swift lovers    IBAction func showSecondControlerAndCloseCurrentOne sender  UIButton        let secondViewController   storyboard  instantiateViewControllerWithIdentifier  ConrollerStoryboardID   as UIViewControllerClass    change it as You need it     var presentingVC   self presentingViewController     self dismissViewControllerAnimated false  completion       - gt  Void   in         presentingVC  presentViewController secondViewController  animated  true  completion  nil

User · Answer

I think you misunderstood some core concepts about iOS modal view controllers. When you dismiss VC1, any presented view controllers by VC1 are dismissed as well. Apple intended for modal view controllers to flow in a stacked manner - in your case VC2 is presented by VC1. You are dismissing VC1 as soon as you present VC2 from VC1 so it is a total mess. To achieve what you want, buttonPressedFromVC1 should have the mainVC present VC2 immediately after VC1 dismisses itself. And I think this can be achieved without delegates. Something along the lines:

UIViewController presentingVC = [self presentingViewController];
[self dismissViewControllerAnimated:YES completion:
 ^{
    [presentingVC presentViewController:vc2 animated:YES completion:nil];
 }];

Note that self.presentingViewController is stored in some other variable, because after vc1 dismisses itself, you shouldn't make any references to it.

[ios] modal View controllers - how to display and dismiss

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