I am presenting a view controller like this:
UINavigationController * PlacesNC = [storyboard instantiateViewControllerWithIdentifier:#"PlacesNavigationController"];
[self presentViewController:PlacesNC animated:YES completion:nil];
Once I am at the final view controller that is presented using the navigation view controller, how can I remove the initial view controller from memory?
Edit
In my application it is possible to present multiple UIViewControllers in this fashion. I will try to give a representation of what my stack might look like.
____ modal vc 5 * current view controller
____ modal vc 4
____ modal vc 3
____ modal vc 2
____ modal vc 1
____ root view controller
So if I have a stack like this, how can I remove vc 1,2,3 and maybe even 4 so that I can release the memory these other view controllers are using up? This may not be the correct to allow such a stack as this, but this is what I have now, and I just need a temporary fix as the iPhone 4 cannot handle the amount of memory used in a stack like this. So until I can come up with an alternate way to present my view controllers I just need to be able to remove some of them from the stack.
You cannot, and you don't want to. It is still in the view controller hierarchy, as I show in this diagram (DrillViewController is presented, but RootViewController is still there, "behind" it):
Presenting a view controller does not destroy the presented view controller, nor should it; if it did, you would not be able to dismiss the presented view controller and find the presenting view controller still sitting there.
Moreover, in iOS 8 it is perfectly possible to present a view controller and show the presented view controller's view in front of the presenting view controller's view, which remains visible behind it. That, for example, is how a UIAlertController presentation works. Clearly it would be a disaster if the presenting view controller ceased to exist in that situation.
Now, it may be that what you really mean is: My view controller has a property that uses a lot of memory. I don't need to hang on to that when my view controller is not frontmost. So I'd like to release it when I present another view controller. In that case, just manage the memory manually: set that property to nil on viewDidDisappear:, and recover its value (somehow) on viewWillAppear: when the presented view controller is dismissed.
One final suggestion: Perhaps the real problem is that a presented view controller was just the wrong type of hierarchical arrangement to start with. Perhaps what you really want to do is replace your original view controller in the view controller with the new view controller - because you are never coming back to it and don't need it any longer. That is perfectly possible, but of course you'll need to set up a different hierarchy architecture.
Related
I'm trying to present a view controller that will be kept displayed above everything, regardless of the currently presented view controller, so it will be kept as displayed even if the view controller behind it will get dismissed, or starts to present another view controller.
I know how to find the topmost view controller (for example as suggested here) but in this case presenting over this view controller will make the new view controller depends on the hierarchy of the parent controller, which I try to avoid.
Present the view from the rearmost view, the window. But give it a high z index so that it shows up in front of everything else.
Recently, I've been reading about the concepts behind dismissing and presenting View Controller. I've been able to pick up on the ideas of dismissing the previous View Controller from the destination View Controller but I can't find an answer to a few questions that have been on my mind for quite a bit.
Scenario 1: I have a login page and after the user enters their credentials, it performs a segue to another View Controller. Is it necessary to dismiss the login page afterwards or is there no reason to?
Scenario 2: I have two normal View Controllers (VC1 and VC2). If I perform a segue to VC2, will I need to dismiss VC1?
I'm mainly confused regarding the idea of when it is necessary to dismiss View Controllers and when it is not necessary to do so.
I'd appreciate it if anybody could help clear these questions up for me.
Scenario 1: After performing a segue, it switches between your view controllers [ automatically dismisses the current ViewController and presents a new one ].
So, there's no reason to dismiss the login page.
Scenario 2: No you don't need to dismiss VC1.
1) When you go from login controller to second controller you just need to present the second controller and no need to dismiss first because if you are using navigation controller as a part of your segue all the view controllers are arranged in form of a stack . So second comes on top and first goes below it.Now if you need to got from second to first you can either dismiss your controller or pop your controller.When you dismiss a controller it is not popped from stack instead just moves behind and let the first controller come on top and when you pop a controller it removes itself from stack as well.
2) Same goes for your second question no need to dismiss first when you go from first to second controller.
If there is a view controller which in most cases will be used only once (like login or settings etc.) — and especially if, after you’re done with it, it makes sense to return to the view controller you were on before — the best is to present it modally and dismiss it when you’re done. The rest of your view controllers stay in memory after the user can no longer see them, and this is expected behavior given the way Apple has created the methods for presenting and dismissing view controllers.
It is my understanding that in the Android world, this is not the case -- the default there is that when a new view controller is presented, the old one really does goes away.
As you know once user has signed in, log in screen not opens until user log out. So you should remove log in view controller from stack, it should not keep in memory. For this task, do not directly perform segue, you should change root view controller. There are lot of answers on stackoverflow for How to change root view controller?
On my main view in a NavigationController I have a button that brings up a new view modally to submit a post. I have a button to dismiss this view which brings the user back to the main view, however if the users proceeds to make a post, I want it to dismiss the view and proceed to a show the post in the Navigation controller.
The ideal effect would have the standard navigation controller's back button on the top that can bring the user back to the main view when they have finished looking at their post.
I have tried several different methods, but I tend to get an error stating "Warning: Attempt to present (The View I Want to Show) whose view is not in the window hierarchy!
Thanks for any info!
Yes, it's possible. This is the best way I've found to structure the app to allow this functionality.
RootViewController
UINavigationViewController
ContentViewController (your current "main" view controller)
You're basically going to create a new RootViewController that is going to contain your current UINavigationController as a child. I usually setup the window.rootViewController programmatically in the AppDelegate. I would also keep a global reference to it.
Have a look at Apple's documentation on this. Basically, the RootViewController code would look like this:
[self addChildViewController:navController];
navController.view.frame = self.view.bounds
[self.view addSubview:self.navController.view];
[navController didMoveToParentViewController:self];
Now, whenever you need to present a modal view controller, present it from the RootViewController, instead of the current/top view controller on the UINavigationBar. This allows you to manipulate the UINavigtaionController independently and you won't get the error you're seeing.
So present the modal view controller from the RootViewController, this covers the UINavigationController and its content (top view controller). Make any changes you need to the UINavigationController stack (push, pop, etc...) with no animation. When you're done dismiss the modal view controller (with animation) and it will show you're adjusted UINavigationController.
Hopefully, this all makes sense. It's kind of complex and hard to explain in text. :p
If you don't want to setup a RootViewController, you might want to try presenting the modal view controller from the UINavigationController, as that might have the same effect. From the view controller just do self.parentViewController.present.
The main thing you're trying to avoid is presenting a modal from a view controller and then removing that view controller (pop) before the modal is dismissed. The view controller that presents the view controller is responsible for dismissing it.
I finally got it all working (I'm still new to Swift) and the two comments on the question were very helpful. The most helpful of all was the top answer here's example on github.
Similar question
Is there a way to present two view controllers at once? My scenario is the following:
From my root view controller (View 0), I want to modally present a view (View 1), and when dismissing that view, a new view (View 2) should be beneath it.
The view hierarchy would look like so:
- View 1
- View 2
- View 0 (root)
I tried presenting it without animations in -viewDidAppear in View 1. This does not seem to be called until the presentation animation is finished, though. And presenting it before -viewDidAppear wouldn't work since the view is not yet in the window hierarchy.
Are there any acceptable ways of doing this?
Presenting a UIViewController while another UIViewController is presenting is not possible without stability issues. As a user experience concern, I think that approach would also not be the best. They should know what to expect when they dismiss a view controller.
If you aren't hard set on using presentViewController: and you have a UINavigationController, instances of that class have a method setViewControllers:animated: that allow you push two UIViewControllers onto a stack. The user would be able to see what they get when they go back (the back item).
Otherwise, you can present on VC, and immediately on success present the other. That's the safest option of doing what you want.
In my app I am queueing some local notifications, when they fire I must present a modal view. The trouble is I have numerous view controllers any one of which could currently be active and thus the one that needs to present the modal view controller. How can I determine which one is currently in use?
I am setting a navigation controller as the windows root view controller, and this can push any number of other view controllers, some of them themselves may also be currently presenting another view controller modally.
This must work on iOS 4 and 5.
I have a lot of view controllers so would like to avoid putting code in each of them to each check if they are currently the top one.
You can look at the navigation controller's topViewController property to find out which controller is at the top of the stack. This will be the one whose view is displayed.
Since you may also be presenting a modal view controller, you'll probably be more interested in the visibleViewController property, which will give you the controller for the current view whether its presented modally or pushed onto the navigation stack.
Create a variable that stores a pointer to the ViewController that was most recently pushed. Every time you push a new ViewController, update this variable. Then you'll always know which one is on the top!