Please help me with this. I have created a simple project with two views as shown. I have attached the images for my storyboard and swift files. So, I read that viewdidload will be executed only once while loading the view into the memory. But, when I make a transition from secondview to the firstview the viewdidload is executing again and so is the print statement in the viewdidload method.
Someone please explain me this.
viewDidLoad is not called once for the Application. It is get called once for that viewController when the view holds memory and loaded.
So as many number of of time you push to the viewController, that many times it will call the viewDidLoad
viewDidLoad() — Called when the view controller’s content view (the top
of its view hierarchy) is created and loaded
viewWillAppear() — Intended for any operations that you want always to
occur before the view becomes visible.
For more info about this look at the link : https://developer.apple.com/library/content/referencelibrary/GettingStarted/DevelopiOSAppsSwift/Lesson4.html
So if the view is already in memory (Like your case), then no need to push again, only need to pop back by this code
self.navigationController?.popViewControllerAnimated(true)
You should not make transition from secondViewController to firstViewController for back. Pop the second view controller by this code to back:
self.navigationController?.popViewControllerAnimated(true)
When you make a transition it makes a new instance from your firstViewController but when you pop the second view controller it dismiss your secondViewController and shows your last viewed viewController again.
Or
in the case that you are not using navigationController you should use below code to dismiss your secondViewController
self.dismissViewControllerAnimated(true, completion: {});
The main point is that you should not use new transition for back.
The simplest way:
1.First embed your ViewController in NavigationController
2.Call to this (instead of create segue for backing)
navigationController?.popToRootViewController(animated: true)
viewDidLoad will be called only once
Related
Throughout my app I use a navigation controller to push and pop my view controllers. When I pop from one ViewController, I check to see if I can reload the data in the previous one with this:
_ = self.navigationController?.popViewController(animated: true)
if let previousViewController = self.navigationController?.viewControllers.last as? AnimalsVC {
previousViewController.tableView.reloadData()
}
This works every time, but now I need to do the same with another view, but it's not apart of the navigation controller because I modally present (instead of pushing it to the navigation controller). Now there's no way I can access the previous ViewController like before and I can not figure out how to access the previous ViewController.
How can I access the previous ViewController to reload the tableview like the example code without accessing the navigation controller?
I know this is possible with notifications, but I prefer not to use that method if possible!
First of all, It's not necessary to access the previous ViewController to reload tableview(or any other func)
I recommend you to use Delegate to achieve the same feature.
Holding a reference to the previous viewController in the way you mentioned will make your app very hard to maintain when your app gets more complicated.
You can call tableview.reloadData() in viewWillAppear method in the controller that you present modally
I am using navigation controller. I have pushed two viewcontroller to navigation stack. When I am coming back to viewcontroller1 from viewcontroller2 using back button of navigation bar then viewdidload method of viewcontroller1 is called again.But as much as I know viewdidload is called only once at loading time. So why is this happening? Please tell me.
Thanks!!
-(void)viewDidLoad called only when view controller is loaded
but if you want to call any method then you can write code in
-(void)viewWillAppear
this method called every time when your view is appear.
About viewDidLoad
viewDidLoad: is called every time your view controller's view is loaded, not just the first time. The controller's view can be loaded and unloaded multiple times during the lifespan of the controller and viewDidLoad will be called every time. It may be unloaded whenever it's not on screen, usually if memory is low.
Best practices
Remember not to do view controller initialisation in viewDidLoad. This is a common mistake. For stuff that should only happen once when the view controller is loaded, do it in one of the controller's init methods.
If you're popping/dismissing back to it, viewDidLoad is not generally called, but viewDidAppear will.
The exception to this is in iOS versions prior to 6.0, if you received a memory warning, your view could be unloaded, and it will be reloaded when you pop back.
As you are pushing the viewcontrollers, AFAIK they create a new instance of the view controller they are presenting. When you get back to viewController1 it's viewDidLoad will not be called but the viewController2 viewDidLoad will be called every time you move from viewController1 to viewController2. When you perform pop from viewController2 it is deallocated there itself
I have 3 view controllers with the NSUserDefault bool values for detecting first launch and calling the tutorial func. But, in one of view controllers, it doesn't work as it should:
I have a custom animated segue with VCs
main vc -> img vc
img vc exit -> main vc
main vc -> sett vc
sett vc exit -> main vc
I tried to write println in the viewDidLoad in main vc and I find out that the viewDidLoad method works only when the app opens, all other time when I come back to main vc it doesn't work. (in two other vcs it works every time when I segue to them)
I have no idea how to correct it.
Your question is hard to understand. I try an answer here, and if it doesn't satisfy your needs, please provide more code.
I believe you mix up a didLoad and a didAppear delegate method.
If you want to trigger code every time a view will be shown to the user, use the viewDidAppear delegate-method.
viewDidLoad is called only once, when the view is loaded to memory. If you use a navigationcontroller and segue back to the view (which is already loaded in memory), viewDidLoad will NOT be called again. But viewDidAppear will
in the viewDidLoad method i have this code.
When the application is running its not go to the another viewController, its gives me an error:
Warning: Attempt to present <CompleteCountryViewController: 0x7fb971779be0> on <ViewController: 0x7fb97176f3e0> whose view is not in the window hierarchy!
What can i do, that when the application running its will go to another viewController?
You should not present a view controller in the viewDidLoad method of another controller because you cannot show a view controller (present modally or push) when a transition is already occurring (push, pop, present, dismiss).
My suggestion is that you move the code in your code sample to the viewDidAppear: method. At this point, you know for sure that the transition has completed.
You seem to have a slight misunderstanding of the lifecycle of UIViewController if you want to modally present a view controller inside the viewDidLoad of another one.
viewDidLoad gets called in one view controller after it has been instantiated and its view components have been loaded (thus the name). The view of that view controller is about to be displayed, so it doesn't make much sense to instantiate another view controller at this point and present it on the first one.
Let me give you an example with two view controller A and B.
You instantiate A and its viewDidLoad gets called. So, A is about to be displayed! What you are doing in your code now is to instantiate B at this very point and show it on A. iOS doesn't like that and will give you your error.
I had an issue where I was attempting to present a modal view controller within the viewDidLoad method. The solution for me was to move this call to the viewDidAppear: method.
View controller's view is not in the window's view hierarchy at the point that it has been loaded (when the viewDidLoad message is sent), but it is in the window hierarchy after it has been presented (when the viewDidAppear: message is sent).
I understand that you can use ViewDidLoad to run some code when a view is loaded. However that only happens once. How can I run a method every single time that view is shown. So for example: let says you are currently in ViewController A and you press a UIButton to go to ViewController B. Then you press a button to go back to ViewController A, how would you then re-run the ViewDidLoad code??
I hope my question makes sense. In essence I want to re-run a small method every single time the user is on a particular ViewController.
Thanks for your time, Dan.
viewWillAppear:
Notifies the view controller that its view is about to be added to a
view hierarchy.
or
viewDidAppear:
Notifies the view controller that its view was added to a view
hierarchy.
This answer didn’t help. I found myself in the same situation and the solution is simple.
Create a method with codes you want to be executed every time your view controllerA shows up.
Place your method under viewDidAppear()
Make sure that the modal type of your viewcontrollerB is set to fullscreen (fullscreen removes viewcontrollerA from the stack)
Under viewcontrollerB viewDidLoad()
Set its background other color than clear. White works for me
Dismiss from your viewControllerB and “voila!”
Create an AbstractController that every view controller inherits from that controller, and you override the viewDidLoad method and make it do whatever you want at every view opened.