My app consists of two views. The first one is a GMSMapView and the second one is used to connect to a Bluetooth device that sends coordinates.
After the Bluetooth device is connected, I use a delegate to send the information back to the map view and move a marker around. To transition between views I was previously using segues, this didn't stop the Bluetooth view controller and the data made its way like I wished to the map view.
I ran into the problem of my map view being reinitiated so I decided to use a navigation controller. Now I use a push segue to get to my second view, and pop to come back to the same instance of the first one. Great, that worked! The issue I have now is that popping the second view seems to stop it completely from running in the background like it used to. Is there a way to keep it running in the background like it did before?
What I'm currently using to pop the second view is
self.navigationController?.popViewControllerAnimated(true)
Any idea would be appreciated! Thanks!
A popped view controller does not "stop running". It is returned to you, and if you don't retain it, it is completely destroyed.
If you don't want that to happen, retain it when it is returned. You are currently ignoring the returned view controller:
self.navigationController?.popViewControllerAnimated(true)
Instead, keep a reference to it:
self.mySecondViewController =
self.navigationController?.popViewControllerAnimated(true)
Be warned, however, that this is a very unusual architecture. You will not be able to use the storyboard segue to push again, because it will push a different copy. It would be better to abandon your navigation controller architecture entirely, as it is completely unsuited to the idea of a view controller persisting after it is popped. If you want an architecture where two view controllers persist simultaneously, you would be better off using a UITabBarController — or, even better, reorganize your app completely. The notion that you need the view controller to persist after being popped is a "bad smell": it means that you have put the functionality in the wrong place. Put the functionality in a place that does persist, rather than forcing the view controller to persist in some artificial way.
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
I got some serious problems understanding the viewcontroller stack.
When will my app use a stack to save the previous viewcontrollers? Only if I use a navigation viewcontroller or anytime I use normal viewcontrollers and segue modally between them?
So I was just wondering if I use some sort of chained routine for example, like going from vc 1 to vc 2 and from vc 2 back to vc 1. No navigation controller, just modal segues, no unwinding.
Does my app got performance issues because of a stack (which will grow everytime I go around) or doesn't it make any difference?
----updated
So basicly this is my problem. If I went through the routine of the app, the views get stacked everytime I do a transtition.
UINavigationController will retain any controller you push onto it's navigation stack until you pop it back off.
Any UIViewController will retain a controller it presents modally until that child controller is dismissed.
In either case every controller will at a minimum consume some memory until you remove it. Apps which construct ever expanding stacks of controllers are likely to encounter a number of issues including:
you will eventually run out of memory, how fast depends on how much memory each controller uses.
you may see unexpected side effects if many controllers in the background react to the same event.
users may become confused if they change state in an instance of controller 'A', push an instance of controller 'B' on top of it, and then "return" to a second instance of 'A' added to the top of the state. Since they're looking at a new controller and view whatever selection, scroll position, user input, or other state they set on the previous instance may be lost.
developers, including you, may come to dread touching this app.
I suspect that everyone will have a better experience if you view controller management matches whatever visual metaphor you are presenting to the user.
so I am building a simple chat app. I will have a login screen, register and later on a UITableViewController so show the friend list. I'm not sure if I should use a UINavigationController for this or just stick to UIViewControllers. Below are two images for the potential setups.:
and:
I'm just wondering is it generally better practice to use a navigation controller? I am also a little confused about what happens to a view controller when it is popped. Does [self.navigationController popViewControllerAnimated:YES]; keep the view controller in the memory to be accessed again later or is a new one created each time? The same question for [self dismissViewControllerAnimated:YES completion:nil], is this destroying the controller or storing it for use later? Thanks
I'll give you my opinion about when to use a navigation controller.
If your app need to present its content in a hierarchical fashion (Master/detail) is pretty common to use a UINavigationController.
If you need to present some content that is not strictly related with the presenting content you can present it using a new view controller on top of it.
Regarding the memory, as soon as you don't keep any reference to the controllers either presented or pushed once remove (popped / dismissed) you loose any reference to them so no space used in memory
I think you will stick to the UINavigationViewController. Simply because the login and registration are belonged to your user management. From the UX standpoints, it's better to use Modal if the scene you are going to present is somehow irrelevant to the current scene. Therefore, go with UINavigationViewController for your situation.
The second question is related to memory management. It's kind of like the reference counting. If you have something to reference the UIViewController, its reference counting won't drop to zero which mean the system won't clean this up. So, you still have way to get then. If you just simply pop then up or dismiss it without referencing it. The reference counting will become zero and the system will clean it.
Note: If you want to simply display a view controller which doesn't need hierarchical navigation or a navigation bar then you wouldn't need to use a UINavigationController.
But in this case I would still suggest to use UINavigationController for the simple fact that your use case (Login Flow) can be completely addressed using a navigation flow.
In terms of memory there is now difference. Feel free to use any of them in this concern. Although how these views are presented has difference.
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).
I am just looking for a sanity check here.
I have a screen that the user passes through on the way into the main application. That screen can be navigated back to from almost anywhere in the system.
As it stands I am just presenting ViewControllers without using a NavController to manage them (it does not seem applicable for most of my app, since screens are not necessarily sequential or related to one another).
My question is, if I have presented VC1, then navigate to other screens, and finally want to present VC1 again, I am doing something like:
[self presentViewController:[self.storyboard instantiateViewControllerWithIdentifier:#"VC1"] animated:YES completion:nil];
Is this bad form? Am I leaking memory by creating a bunch of VC1 instances or is there some magic that uses the previously created one?
If it is bad form, how do I get back to the original VC1 to reuse it?
Thanks for any input.
I think you pegged it: It's not a great idea to have multiple instances of the same view controller in memory at the same time. Every time you instantiate a new view controller and present it modally, you'll consume more memory.
The most elegant solution is the iOS 6 unwind segue. But most of us would be unwilling to give up on iOS 5 support quite yet.
If you need to support iOS 5, you could contemplate using navigation controller, but hide the navigation bar if you don't like it in your user interface. Then replace modal segues with push segues and now you can do popToRootViewController whenever you want to return to the main view controller.