I'm new to iOS dev and am not entirely sure on Storyboards/Segues/Pushing and Popping.
So in my app I have a navigation controller with 5 view controllers leading from one to another.
When it reaches the last view controller i have a segue to the first and I have a few tasks listed in the prepareForSegue method.
Out of curiosity I decided to check what happens to the [self.navigationController.viewControllers count]. I found that it keeps growing and growing which doesn't 'feel' correct.
Am i handling going back to the first screen correctly? The prepareForSegue method is useful as it allows me to send some data back to the first segue. Is it possible to maybe say when you go back clear all views on that navigation controller?
Thanks
You can use an unwind segue. Here's a good tutorial:
pragmaticstudio.com/blog/2013/2/5/unwind-segues
Make sure to create the unwind action method before you wire it up in the storyboard otherwise it won't show up when you drag to 'Exit'. That was the most confusing part for me when I first set one up. The tutorial does it in the correct order so if you follow it you should be fine.
Also, here's a sample I put together showing how to transfer data back in an unwind segue. It uses a modally presented view controller but the technique is the same:
github.com/soleares/AddToTableView
No, you should never go backwards with a segue (other than an unwind). Segues ALWAYS instantiate new controllers, so you're not actually going back to the first controller, you're just creating a new instance, which gets added to the stack. So either go back with an unwind segue or use popToViewController:animated:. Using an unwind segue will allow you to use prepareForSegue, and it does cause all the controllers in between to be deallocated (if you have no other strong pointers to them).
Related
I have been searching all over the web but I can't seem to find the answer to this.
Currently i am using presentViewController to start new ViewControllers, but on certain view controllers i do not dismiss it and call over it. I currently am not using any navigation controllers or anything like that.
I am just worried that if I call the same viewController again via presentViewController, that the same viewController would have 2 running instances.
Is it possible? Or does the iOS framework automatically reuse the idle viewController?
If so, how do i remove the idle view controllers?
Thank you! (I was holding back my question and tried to find it all over the web, so if you can point me in the right direction, it would be very helpful thanks!)
iOS will not reuse your view controller, you can easily check it yourself by printing your view controller in viewDidLoad, you will notice first that viewDidLoad is called every time, and next that all objects have different addresses.
Unless you create thousand of them, or the navigation of your app doesn’t let you come back to an “idle” view controller, I would not say this is an issue though.
I don’t see any clean way to remove a view controller from the memory without calling “dismiss”. You could try to:
- “refresh” your view with new data.
- use something like UIPageViewController if the workflow of your app allows this kind of behaviour.
- rework the navigation so you can dismiss the view before calling another one
Good luck
From an initial ViewController I've modally presented a second ViewController using a ShowDetail segue in the storyboard and a performSegueWithIdentifier: method call. The problem is when I dismiss this modal ViewController with the method dismissViewControllerAnimated: the initial ViewController is reinstantiated calling the viewDidLoad again.
I've tried using a Push segue instead of the Show Detail and the initial ViewController keeps allocated in the background as it should.
What might be going on? The initial ViewController never even calls the memory warning method.
Have you tried unwindSegues?
***** Long explanation ahead, skip to solution if you want the quick way *****
First of all, if it is a ShowDetail, it is not a modal view. Do try to see which is your case.
Modal segues can carry information backwards, but are a bit more complicated than push ones.
If you are modally presenting it, you should use Present Modally instead of a ShowDetail.
A modal presentation will always take the top view position in the stack, and Show Detail does as well, depending in how your views are set. For instance, if you have a detail view in stack, IT will be replaced rather than the stack top view.
Try choosing up to a specific segue, I particularly recommend modal assuming you need more than simple pushes (Or the Show would have closed the problem, being the equivalent to the previous deprecated push. If you only need something simple, Show is the way)
Now we've cleared this, what probably is happening is that the view is being removes since Show Detail replaces views instead of pushing them, and it has to perform init again.
***** Solution: *****
The solution then should be not to lose the view when replacing, and reinitializing it, what dismissViewControllerAnimated: does. If you use unwind segues, though, the view should be replaced BUT retained by ARC.
The following link has the best explanation all over the net about how to use it:
What are Unwind segues for and how do you use them?
I have a category on UIViewController that deals with errors coming from my networking layer. If I get an authentication error in response to a network call, I want to perform an unwind segue which takes me back to my LoginViewController.
However, I don't want to have to add the appropriate unwind segue to every single view controller in my Storyboard. Can I simply declare the unwind segue in the UITabBarController that is at the "top" of my view controller navigation, and then say
[self.tabBarController performSegueWithIdentifier:#"UnwindToLoginSegueIdentifier" sender:self]
... from inside my UIViewController+ErrorHandling category?
No, you can't do that. The unwind segue has to come from the controller you're unwinding from, and all segues need to be connected from a particular instance in the storyboard. The login view controller really should be one that's presented modally, not be one of the tabs, since you only need it briefly, then it should go away. If you set up your app that way, you can present and dismiss it from any controller (present it without animation from the controller in the first tab, if that's what you want the user to see when the app launches). You'll still have to have code in every controller to do that, unless you make a common base controller with that functionality that all the other controllers inherit from.
The app I'm working on will need to implement a workflow to allow users to enter information in a form. Instead of using a scroll view, I'm planning to break it up into a bunch of separate view controllers, which will be managed by a navigation controller. I started by laying out all the form fragments in a storyboard, and began connecting all the push and unwind segues for the different parts of the form.
My question is, how is using all these push and unwind segues any better than simply using the pushViewController and popToViewController methods of my navigation controller, and skipping the storyboard altogether? Is there any difference in terms of memory management or performance? Wouldn't simply using push and pop be better practice in terms of design and maintainability? I can't find anything in the docs that addresses this.
There's basically no difference in terms of what they do. The one thing that's good about using unwinds, is that you can pass data back to the controller you're unwinding to. If you use the pop methods, then you have to create a delegate protocol to do this. But a lot of this is subjective. You can use which ever is more comfortable for you. I like using the storyboard because it makes it easy to see the relationships between the controllers. Using storyboards can be a problem (so I've heard anyway) when you are working in a large team, so that's another consideration.
This is a great question.
In my 1st iOS project I followed the tutorials online and used storyboard segues etc. In my 2nd iOS project, I scrapped that and just push and pop view controllers.
I actually find it cleaner because with the storyboard way, you have to call performSegueWithIdentifier, and then you can prep the receiving view controller by sync'ing up with prepareForSegue. Why do this when you can just prep a view controller and push it all in one place?
Additionally, it decouples view controllers with transitions. It opens everything up and allows for more versatility..and more rapid development.
So my take on the matter is to just push and pop view controllers. Maybe somebody will make me look dumb but I've had much success just using this method.
For this case
(NAV_A --root view controller -- VC1) -- modally presents -- (NAV_B -- root view controller -- VC2 -- push -- VC3)
If you do pop at VC3 you will always reach VC2, ie view controller just below it.
With unwind you can do what you did above plus , jump back to VC1 in one go.
Unwind can take you back to any point in the view controller hierarchy that you want but not pop.
I created a storyboard for my app which contains the following:
Initial view controller on my storyboard is a Tab Bar Controller (let's call it myTabCtrlr)
myTabCtrlr has forward segues pointing to several other controllers:
a. First segue points to a custom UIViewController (let's call it vc1) on which I create an interactive UIView (let's call it popview1) which is initially hidden. There's a button (let's call it showPopView1) on vc1's view which when clicked would show popview1
b. Second segue points to a navigation controller, which embeds a view controller with 3 buttons, each pointing to an (end) controller.
c. Third segue points to another navigation controller with a similar setup as (b)
On several of these (end) controllers, there's a button similar to vc1's showPopView1 that when tapped, I'd like to switch back to vc1 and programmatically bring up popview1, which I'm doing as follows (but it's not working):
myTabCtrlr.selectedIndex = 0;
//I get a handle to vc1 then
vc1.popview1.hidden = NO;
When I do that, it goes back to the first tab and shows vc1 view (which is good) but it does not show popview1. I tried many different ways to do it but no luck.
Note that if I'm actually on vc1 and I tap the showPopView1 button, then popview1 comes up normally.
Does anybody know why that is the case? This only started after I transitioned to using storyboard. thanks.
After spending hours looking at various ways to solve this problem, and focusing on reverse segues and similar methods, I was able to solve it using a totally different method.. I wanted to share this with others so nobody has to waste so much of their time (although I noticed slow response to my post. Maybe I didn't make the subject attractive enough :)..
It's a really simple solution, but quite effective. I used a Singleton pattern object. When coming from the rest of the tabs, I set a flag in the singleton that vc1 checks in its viewWillAppear method, shows popview1, and immediately resets the flag.. works like a charm!