I have a view controller. It has some data and values in it. Then it presents modally to another view and moves around and some stuff happens. Then at some point, you self.dismissViewController(). Once back at the original view, can I count on the original data being there? Any help is greatly appreciated. Thanks in advance!
They will not be affected unless you specifically write code to do that for you.
For example, if you call a network request in the viewDidLoad() and add the data to some views, labels, etc. Then you leave that ViewController and come back, nothing will change, i.e., the network request will not be called again.
If you do want to change values in the ViewController every time it appears, use the viewDidAppear() delegate method.
for reloading view on dismiss you must use viewWillAppear() because this working every time before rendering view
calling dismissViewController will remove the viewController. If you do not have a strong reference to the view controller stored elsewhere, dismissing it releases the memory associated with it.
If the presented view controller must return data to the presenting view controller, use the delegation design pattern to facilitate the transfer.
So if the data was not modified in the presented controller then it will be the same then you can depend on it
reference: Apple docs
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 am not even sure how to title this question. I will change the title as you might suggest later.
Basically, I have a sliding view controller for my side menu. Login view controller is above the sliding one. So I want data in my sliding view controller to be reloaded when login is complete and I open side view. I have tried to use delegation, but could not figure out how to set sliding view as delegate for login view controller.
What would be the best approach here. I am using ECSlidingViewController for side menu. Maybe there is a way to reload view controller using self.storyboard or something else?
Thank you.
Why don't you update the data when its -viewWillAppear is being called? If the view isn't visible, does it really matter to update its contents? I'm assuming that your slidingviewcontroller does the right thing and shows and hides its views so that viewWill/DidAppear and ...Disappear are all getting called.
If you have to update it, then I wouldn't necessarily use delegation. If the slidingviewcontroller is a persistent object and always available, say via the rootviewcontroller, then declare a method, such as -updateData, and call it directly.
For example:
slidingViewController = self.rootViewController.slidingViewController;
[slidingViewController updateData];
Alternatively, you may have to get the rootViewController from your ApplicationDelegate or window. Depends on where you have slidingViewController and rootViewController stashed away.
Hi all I am doing a course in Udemy, and the code calls for placing code in the viewDidLoad function as shown below:
override func viewDidLoad() {
super.viewDidLoad()
placesArray.append(["name":"Taj Mahal", "lat":"27.175607", "lon":"78.042112"])
}
The array append should only run once, however, when I segue to another viewController and come back, it runs the code to append again. So I now have an array with 2 rows, both of which are Taj Mahal.
I thought that the viewDidLoad function only runs code once?
Is there a way around this?
Thanks.
Addendum:
I am using Swift, so I don't see any alloc and init while creating and launching the viewController. And weird as it sounds, the video tutorial has it working in the viewDidLoad and the trainer is using the storyboard to segue from the initial table view controller to a map view on a view controller and just has a back button on the map view that segue's back to the table view controller via the storyboard as well. - Could be because I have the latest version of the Swift language and the trainer was using an earlier version, (cause I noticed some slight differences in coding earlier) but you never know. Either way whenever he touches the back button it does not run the append code anymore.
I am trying to get in contact with the trainer as some of the suggestions here, though they are good don't seem to work.
I will put the solution in here once I get in contact with the trainer.
The viewDidLoad method is called when your view controller's view finishes loading. The view will load when a view controller's view property is nil and something attempts to access it.
UIViewController *myVC = [[UIViewController alloc] init];
UIView *aView = myVC.view; // this loads myVC's view; viewDidLoad is called when it completes loading.
If the view has unloaded (usually due to memory limitations), it will be called when the view property is next accessed.
Manipulation of data sets should generally not be done within view methods. Consider moving this to the init of the view controller (or to a different "datasource" class).
I suppose you are trying to do data initialisation in viewDidLoad. If there is no other operation on placesArray before viewDidLoad, then instead of append, what about setting the placesArray directly:
placesArray = ["name":"Taj Mahal", "lat":"27.175607", "lon":"78.042112"]
Then even if your view is unloaded for some reasons. Taj Mahal will still be added once only.
viewDidLoad is called whenever the view controller's view property is set. When does this happen? It depends on how the view controller is contained:
UINavigationController
- View Controller views are loaded as they are added to the navigation stack and "unloaded" (although the viewDidUnload method is deprecated) as they are removed.
UITabBarController
- View Controller views are loaded as they are added to the tab bar regardless of whether they are on screen or not. They stay loaded as you change from tab to tab.
Depending on your needs and use case, you can create your own view controller container that does what you need. Checkout the Apple docs on the proper way to do this:
https://developer.apple.com/library/ios/featuredarticles/ViewControllerPGforiPhoneOS/CreatingCustomContainerViewControllers/CreatingCustomContainerViewControllers.html
I'm having a slight problem with iOS. I am passing data back and forth between two view controllers using protocols and manually switching views. My problem is that when I dismiss the top view, viewDidLoad for the bottom view isn't called again. Since I'm sending information from my second view to my first view, I need viewDidLoad to be called so I can handle the information I'm passing. If you have any ideas on how to do this, any help is appreciated. Thank you.
- (void)viewDidLoad {
[super viewDidLoad];
}
Is called exactly once, when the view controller is first loaded into memory. This is where you want to instantiate any instance variables and build any views that live for the entire lifecycle of this view controller.
- (void)viewDidAppear:(BOOL)animated{
[super viewDidAppear:animated];
}
Is called when the view is actually visible, and can be called multiple times during the lifecycle of a View Controller (example when a Modal View Controller is dismissed and the view becomes visible again)
use -(void)viewDidAppear:(BOOL)animated instead of viewDidLoad
I am passing data back and forth between two view controllers using protocols and manually switching views. My problem is that when I dismiss the top view, viewDidLoad for the bottom view isn't called again. Since I'm sending information from my second view to my first view, I need viewDidLoad to be called
No you don't, and the fact that you think you do makes me think something else may be going wrong here.
Consider this: if you are truly passing data back from the second view controller from the first, then the first view controller has the data and can update itself now. It exists, and it has a view. So it should update itself on the spot, as you hand it the data. Then, when you dismiss the second view controller, the first view controller's view will appear - already updated. In effect, dismissing the second view controller merely reveals the first view controller's view, which was there all along, and was updated even though it wasn't showing.