Dismissing a Presented View Controller

Question

I have a theoretic question  Now I m reading Apple s ViewController guide   They wrote       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    But I can t explain  why I have to create a protocol in presented VC and add delegate varible  create delegate method in presenting VC for dismissing presented VC  instead of a simple call in presented view controller method    self dismissViewControllerAnimated NO completion nil     Why is the first choice better  Why does Apple recommend it

User · Answer

I like this one           viewController navigationController  presentingViewController                viewController presentingViewController                viewController  dismiss animated  true

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Swift 3 0   Dismiss View Controller in swift   self navigationController  popViewController animated  true  dismiss animated  true  completion  nil

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try this    self dismissViewControllerAnimated true completion nil

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One point is that this is a good coding approach  It satisfies many OOP principles  eg   SRP  Separation of concerns etc    So  the view controller presenting the view should be the one dismissing it    Like  a real estate company who gives a house on rent should be the authority to take it back

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Swift  let rootViewController UIViewController    UIApplication shared keyWindow  rootViewController            if  rootViewController presentedViewController    nil                rootViewController dismiss animated  true  completion                      completion block

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In my experience  it comes in handy when you need to dismiss it from any ViewController you want and perform different tasks for each viewcontroller that dismisses it  Any viewController that adopts the protocol can dismiss the view in it s own way   ipad vs iphone  or passing different data when dismissing from different views  calling different methods when dismissing  etc     Edit   So  to clarify  if all you ever want to do is dismiss the view  I see no need to setup the delegate protocol  If you need to do different things after you dismiss it from different presenting view controllers  It would be your best way to go using the delegate

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In addition to Michael Enriquez s answer  I can think of one other reason why this may be a good way to protect yourself from an undetermined state   Say ViewControllerA presents ViewControllerB modally  But  since you may not have written the code for ViewControllerA you aren t aware of the lifecycle of ViewControllerA  It may dismiss 5 seconds  say  after presenting your view controller  ViewControllerB   In this case  if you were simply using dismissViewController from ViewControllerB to dismiss itself  you would end up in an undefined state--perhaps not a crash or a black screen but an undefined state from your point of view   If  instead  you were using the delegate pattern  you would be aware of the state of ViewControllerB and you can program for a case like the one I described

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I think Apple are covering their backs a little here for a potentially kludgy piece of API       self dismissViewControllerAnimated NO completion nil    Is actually a bit of a fiddle  Although you can - legitimately - call this on the presented view controller  all it does is forward the message on to the presenting view controller  If you want to do anything over and above just dismissing the VC  you will need to know this  and you need to treat it much the same way as a delegate method - as that s pretty much what it is  a baked-in somewhat inflexible delegate method    Perhaps they ve come across loads of bad code by people not really understanding how this is put together  hence their caution    But of course  if all you need to do is dismiss the thing  go ahead   My own approach is a compromise  at least it reminds me what is going on       self presentingViewController  dismissViewControllerAnimated NO completion nil     Swift     self presentingViewController  dismiss animated  false  completion nil

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This is for view controller reusability   Your view controller shouldn t care if it is being presented as a modal  pushed on a navigation controller  or whatever  If your view controller dismisses itself  then you re assuming it is being presented modally  You won t be able to push that view controller onto a navigation controller   By implementing a protocol  you let the parent view controller decide how it should be presented pushed and dismissed popped

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Quote from View Controller Programming Guide   How View Controllers Present Other View Controllers       Each view controller in a chain of presented view controllers has   pointers to the other objects surrounding it in the chain  In other   words  a presented view controller that presents another view   controller has valid objects in both its presentingViewController and   presentedViewController properties  You can use these relationships to   trace through the chain of view controllers as needed  For example  if   the user cancels the current operation  you can remove all objects in   the chain by dismissing the first presented view controller    Dismissing a view controller dismisses not only that view controller   but also any view controllers it presented    So on one hand it makes for a nice balanced design  good de-coupling  etc    But on the other hand it s very practical  because you can quickly get back to a certain point in navigation    Although  I personally would rather use unwinding segues than try to traverse backwards the presenting view controllers tree  which is what Apple talks about in this chapter where the quote is from

User · Answer

This is a lot of baloney   Delegation is fine when it is needed but if it makes the code more complex -- and it does -- then there needs to be a reason for it   I m sure Apple has its reasons   But it is clearer and more concise to simply have the presented VC do the dismiss unless there is a true reason for doing otherwise and no one here as of today has presented one that I can see     Protocols are excellent when they re needed but object oriented design was never about having modules communicating unnecessarily with each other     Tom Love  co-developer of Objective C  once commented that Objective C was  elegant    small    crisp  and  well-defined   when comparing with C      Easy for him to say   Delegation is a useful feature that seems to have been over-used  just because   and while I like working in the language  I dread the idea of felling compelled to use unnecessary syntax to make things more complex than they have to be

User · Answer

If you are using modal use view dismiss    self dismissViewControllerAnimated NO completion nil

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Updated for Swift 3 I came here just wanting to dismiss the current  presented  View Controller  I m making this answer for anyone coming here with the same purpose  Navigation Controller If you are using a navigation controller  then it is quite easy  Go back to the previous view controller     Swift self navigationController  popViewController animated  true      Objective-C  self navigationController popViewControllerAnimated YES    Go back to the root view controller     Swift self navigationController  popToRootViewController animated  true      Objective-C  self navigationController popToRootViewControllerAnimated YES     Thanks to this answer for the Objective-C   Modal View Controller When a View Controller is presented modally  you can dismiss it  from the second view controller  by calling    Swift self dismiss animated  true  completion  nil      Objective-C  self dismissViewControllerAnimated YES completion nil    The documentation says   The presenting view controller is responsible for dismissing the view controller it presented  If you call this method on the presented view controller itself  UIKit asks the presenting view controller to handle the dismissal   So it works for the presented view controller to call it on itself  Here is a full example  Delegates The OP s question was about the complexity of using delegates to dismiss a view   This Objective-C answer goes into it quite a bit  Here is a Swift example   To this point I have not needed to use delegates since I usually have a navigation controller or modal view controllers  but if I do need to use the delegate pattern in the future  I will add an update

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You can Close your super view window  self view superview  window  close

[iphone] Dismissing a Presented View Controller

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