Unwinding a segue to a programmatically specified unwindSegue (without Storyboard) - ios

I still don't have an answer after viewing many answers to a similar question eg. https://stackoverflow.com/questions/12509422/how-to-perform-unwind-segue-programmatically
I would like to try to restate what "programmatically" means to the question I'm posing.
All the solutions show using a storyboard and connecting the view controllers "exit" with an unwind method defined in some view controller. This works but isn't programmatically, but rather directly connecting through use by the Xcode tool. Sure the prepare method is programmatically involved in the final steps.
My challenge is that I'm using Cocoapods as a reusable library, and the storyboard has no way to know about users of this library. So they cannot connect to an unwind method, as there isn't one yet.
I want to use the language generic capabilities to specify the unwind method, programmatically (Swift or Objective-C).
The unwind method might also be in another bundle, further complicating things.
Note: Creating a placeholder unwind would be ok, assuming the value of the view controller name can be changed programmatically through the UIStoryboardSegue object (which has an unwindAction).
Thanks for any insight.
UPDATE ANSWER (it won't let me answer)
First, my answer involves clarifying the original question, in particular the "without storboard" statement. This was meant to "unwind" to a ViewController that wasn't specified via the storyboard, in particular a new user of this library. My answer shows I can do this, but a storyboard is still required (just not for this new ViewController).
My question did state that a placeholder unwind could be created via a storyboard.
Note: Creating a placeholder unwind would be ok, assuming the value of the view controller name can be changed programmatically through the UIStoryboardSegue object (which has an unwindAction).
So my answer can call code that wasn't specified via the Xcode user interface (which is the UI process of connecting to a named unwind though dragging to the 'exit').
I was under the (wrong) assumption this was connecting to my unwind method (eg. unwindFromHelp), much like connecting a button to an IBAction in code. Instead it connects dynamically to anything matching that name in the runtime hierarchy.
The key insight to the answer is from What are Unwind segues for and how do you use them? where #shawkinaw states:
In other words, think of the unwind action as describing where the segue is coming from, rather than where it is going to.
This also means there can be many implementations of the same unwind method name! At runtime, the ViewController hierarchy keeps track of the unwind methods it's encountered along the way, and calling the Segue Unwind will unwind to the first one it finds.
Based on that new understanding, my quest to call an unwind method in some future ViewController is possible by creating a placeholder unwind that is manually added through the Xcode exit approach. That operation shows all the unwind methods available at that time.
So the solution involves using the storyboard, and a (potentially) unused ViewController, where an unwind method is defined. Then the exit of the desired ViewController connects through Xcode to that unwind.
A future user can also define this same unwind method in new code (eg. unwindFromHelp) and if the ViewHierarchy runtime stack is such that no other unwind is matched, their code is executed. Thus this delegation approach achieves my original question, where the future user must provide an implementation for the delegation (which here is an unwind method name, eg. unwindFromHelp).
I wrote a sample that shows how this can be accomplished and the unwind returns to different ViewControllers based on how it got there: github UnwindExample
An example flow diagram is based on the
A or B calling Help idea.

Related

Is there a way to create an unwind segue programatically?

I want to extend the view controller to have an unwind segue.
I know how to create an unwind segue via the storyboard but I do not want to create an unwind segue for every view controller.
I already know how to do this, what I am asking for is how to do this programatically:
Thanks.
Please read comments

You can't. An unwind segue can be created only from Interface Builder, but can be triggered programatically. It least for now.
Technical Note TN2298 - Using Unwind Segues
There is no direct indication of the fact that it is forbidden, but the document describes only the one way to create unwind segue. Well, I've never heard or seen the solution to create unwind segue programatically too.

Is there any way to create and use an unwind segue programmatically?

I have a series of three view controllers, the first two of which are wrapped in a UINavigationController, and are managed by the default Main.storyboard file. Let's call them A and B, respectively. I have more view controllers throughout the file, each instantiated and managed separately, though I am working on moving them into all-code solutions. The aforementioned third view controller I have already in code (C) is one that at various times is instantiated and presented by B.
A and B have a normal segue relationship setup in Interface Builder and called via code. I do the same with C from B, via code (instantiate and presentViewController(_:)). There are a few cases where an action in C invalidates B's raison d'être, and thus I must dismiss both.
So far, I have been calling dismissViewControllerAnimated(_:) from C, and then checking in B's viewDidAppear(_:) whether it should be dismissed, and dismissing it the same way if so. During this process, the user is thrown back though the VC hierarchy, watching as empty views fly back to whence they came, leaving time for them to experiment with controls that no longer work, and may crash the app. This is a rather disconcerting user experience that I wish to do away with. I could simply disable everything, but that's a lot of controls that I'd rather not mess with if I can avoid it...
I understand that IB supports "unwind segues," which can dismiss an entire VC hierarchy simultaneously, though those only seem to handle view controllers in the storyboard. Is there any way to get this behavior (dismiss everything to A) programmatically, without having to revert much of the work I've already done, considering that part of my hierarchy is contained in a UINavigationController?
UPDATE:
So, I got the dismissal to work properly, by passing a reference to the presenting view, and calling its dismiss segue before leaving. That approach came with its own issues and navigation controller weirdness, but with some tweaking it might be usable.
Honestly, it would be much easier to remove the feature entirely at this point, as it's mostly a convenience.
For the sake of science, I'm going to keep at it until I decide ether way, and answer back here for anyone googling this way.
UPDATE:
Ew... It seems this code was older than I thought. I actually have two navigation controllers, to support a custom modal animation into and out of B, with a custom unwind segue there (there you go). In order to get the animation I want, I may as well toss C into the storyboard and make a custom unwind segue.
If I don't care about animation, simply disabling animation on the custom unwind got both B and C to vanish promptly, and together. Trouble is, it's a bit jolting for my taste...
vacawama's suggestion actually makes a lot of sense, and serves me right for not checking the documentation! UIViewController already keeps a reference to its presentingViewController. Going back by two is a pinch, simply climbing back that hierarchy and dismissing the one I want. Works like a charm, without animation doesn't happen at all...
Gonna post an answer here soon with what I've found thus far.

So, science prevails, and a solution is found.
It's really a pain to do if you don't like writing custom segues and animators. Gonna do that eventually, but for now it's more profitable to just not enable the feature at all. (Thank goodness it's easy to toggle on my end).
I found that running my dismiss segue (I use a custom one) on B, then dismissing C did the trick, so long as I didn't use animations for either. Nothing unexpected there at all!
Further, I could get the same effect in one line (animation doesn't matter, so neither does custom segue) by running:
presentingViewController?.presentingViewController?.dismissViewControllerAnimated(true, completion: nil)
from C's equivalent of goAllTheWayBack().
Gross, but it got the job done. A bit more tweaking, like actually using the storyboard (ugh) for its unwind segue and writing a custom animator, it'd look fancier than a pig in a blanket!
I'd about declare this horse good and dead. Thanks all!

Have you tried Atomic Object's approach
TL;DR
use IB and ctrl-drag 'C' view controller (yellow) to 'Exit',
select 'prepareForUnwind',
give the unwind segue an identifier,
then you can perform the unwind programmatically and it will skip 'B' view controller.

Change segue endpoint using Storyboard

How do you change the endpoint of an existing segue using storyboard?
Obviously I can delete and re-create the segue but this adds a potential for "operator error". Eg if I accidentally mistype the segue's identifier, the code will later crash.
Storyboard doesn't seem to offer this really simple functionality. Can't drag the segue to somewhere else, can't see any config items that refer to its endpoint. Or am I missing something obvious?

Yes, you can't change endpoints of existing segue. You have to create new one. You can't drag and drop endpoint to some viewcontroller to other.
And there is no need of it also.
For example, let's assume scenario like : You have one view controller called A, and you have given segue from A to another Viewcontroller B and segue name is segueToB. Now you have another viewcontroller say C and now you want to give segue from A to this C then make Another segue. no need to delete segueToB. Create segueToC which points A to C. Now when you want to go from A to B then perform segueToB segue. When you want to go from A to C then perform segueToC segue. Likewise you can make multiple segue. There is no need to change endpoint or delete segue and change identifier everytime.

Differences between presentViewController and performSegueWithIdentifier

This is a kinda conceptual question (not trying to solve a particular problem but to understand things better) that I encountered.
IBOutlets in view controllers are "forcedly unwrapped" variables by default and I don't know exactly why but it tells me that iOS expects each one of them to be initialized when the VC is called.
I have a view controller A and two other ones B and C. I have a click listener to a custom button of mine in A that depending a certain variable, decides after the click if B or C are going to be called.
I tried implementing this with presentViewController but for some reason my program crashed in runtime because of non-initialized outlets in either B or C.
However, I named by segues and tried the same thing with performSegueWithIdentifier and it just worked.
I wanna know, what are all the differences between them and is everything I told I know correct?
Thanks in advance

How to safely try to perform segue in Swift while ignoring/handling manually possible exceptions?

I'm trying to make a custom view controller for use in my projects, that has possible 3 segues from it. But those are not mandatory.
When view controller loads i'm calling a method "trySegues()" that should try to perform all 3 of those segues. Segues are custom, so each successful call will be handled and registered in my code.
In Objective-C i would do that using "#try - #catch" so all the successful calls will go forward, while if one of those segues is not set, it'll raise an exception, but it will be handled by me manually so it won't break the execution of the program.
Is there a way to do the same in Swift?
Using Optionals to simulate an exception won't work, since the performSegueWithIdentifier function returns no value.

In no imaginable way is #try-#catch-ing a performSegueWithIdentifier: the appropriate approach to this challenge. Not in Objective-C. Not in Swift.
Segues can't (or shouldn't) exist independently of storyboards. After all, if you were try to instantiate a segue, the class name is UIStoryboardSegue. The fact that this class even exists publicly is not so that you can instantiate it and add it at run time. It exists so that you can subclass the segue, choose your subclass on the storyboard, and set up a segue with custom behavior:
In Objective-C and Swift, exceptions are reserved for truly exceptional behavior. Behavior which can be prevented at development time. We should not be relying on #try-#catch blocks during run-time by the time we've released our app. We should have fixed our app so that there's nothing to #catch.
So with this said, the only way that performSegueWithIdentifier: can throw an exception is if the segue identifier we gave it does not exist. The only reason the segue shouldn't exist is because we made a typo somewhere.
The segues are hooked up and defined at compile time. There is no public mechanism for checking whether or not a particular segue exists because we just shouldn't be doing this at all.
Now, with all that said, if we want to dynamically push or modally present a particular view controller at run time, and we can't know at compile time what view controller it will be (or from what view controller we're getting to it from), then we shouldn't be presenting it via a segue.
Instead, we should be using one of the presentation options the UIViewController class defines.
Your options are:
presentViewController(_:animated:completion:)
showViewController(_:sender:)
showDetailViewController(_:sender:)
And in place of an unwind segue, you'd want something like this:
dismissViewControllerAnimated(_:completion:)

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