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).
Related
I have a view controller that is a child view controller of my window's root view controller. That child view controller has a table view and when i select a row it tells the parent view controller to present a view controller modally. The modal view controller, however, never appears. I created a bare bones test view controller that just prints viewDidLoad and viewWillAppear. What I notice is that when I call parentVC.present(testVC, animated:true, completion:nil), viewDidLoad is run, but viewWillAppear is not. viewWillAppear is only then called when I interact with the UI in some way. Whether tapping, panning, scrolling or whatever.
I've spent hours trying to debug this. It doesn't seem like the main queue is blocked and I've reduced the problem to its bare bones. The modally presented view controller's viewWillAppear is simply not called until I interact with the UI again.
What could be causing this symptom?
In comments, you mention that you're instantiating your view controller with
let vc = TestVC()
where TestVC is presumably a (largely empty) UIViewController subclass.
A view controller needs a view created either via either storyboard scene (using instantiateViewController), a NIB or, in very rare cases, a view you create in loadView (which you shouldn’t be confused with viewDidLoad).
I’d suggest creating a storyboard scene (assuming you are using storyboards), give it a storyboard ID, and then use instantiateViewController:
let vc = storyboard.instantiateViewController(withIdentifier: "foo")
But just having a UIViewController subclass called TestVC and instantiating it with TestVC() won’t work.
In our discussion, you said you wanted to do this programmatically with no NIB nor storyboard. If so, use loadView. See https://stackoverflow.com/a/37964249/1271826 for an example.
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 need a loading screen to show while some data is being downloaded from the server. I present a view controller with modal segue without animation. But I don't know how to dismiss the loading screen view controller since dismissViewController function can only be called from inside.
I should be able to dismiss the loading screen view controller from another view controller. Any suggestions?
One option is using NSNotificationCenter. You can post custom notification and listen it in loading view for closing it.
If you are getting the data in parent view then you can close the loading view from parent view also. You can call dismissViewController from parent view using presentingViewController property of UIViewController class.
In your case from parentView you can dismiss the child view using:
[self.presentingViewController dismissViewControllerAnimated:YES completion:nil];
presentingViewController
The view controller that presented this view controller. (read-only)
Declaration
Swift
var presentingViewController: UIViewController? { get }
Objective-C
#property(nonatomic, readonly) UIViewController *presentingViewController
Discussion
When you present a view controller modally (either explicitly or
implicitly) using the presentViewController:animated:completion:
method, the view controller that was presented has this property set
to the view controller that presented it. If the view controller was
not presented modally, but one of its ancestors was, this property
contains the view controller that presented the ancestor. If neither
the current view controller or any of its ancestors were presented
modally, the value in this property is nil. Import Statement
import UIKit Availability
Available in iOS 5.0 and later.
Do you need to show another VC? You could just show a subview, making it visible=true when you start the app, and on the request success or failure callbacks hide it again (depending on the networking framework you are using)
I don't know were you start the request and were you know when it is done, if the loading screen knows when the download is finished you can do one of two things, or you pass the first VC as a delegate (defining a protocol) to the second VC (loading screen), and when you know on the loading screen that the download is finished you call a method on the delegate that will dismiss the loading screen,
Or you can use NSNotificationCenter, register for some kind of events on the first VC and when the process finishes on the loading screen you notify the first VC with this method, to dismiss the loading screen.
If you start the process on the first VC, and you know when it ends also on the first VC I would not understand your question, as you would just dismiss the loading screen and it would work.
Could you give more info? If you'd like I can post some code in order to help you in one of this approaches.
I'm trying to figure out something about the view controller lifecycle, i understand that viewdidload gets called only once.
BUT, I have a situation were i have 2 view controllers, one is the main view controller and another table view controller.
In the main view controller i have 2 buttons, one for the table view and one to some other view.
The main vorw conrtoller viewdidload does happends once but, Whenever i modal to those other view controllers viewdidload gets call each time.
Im using [self presentviewcontroller: self.navigationcpntroller animated:yes completion: nil]
To modal to the other view controllers from my main view controller. And im using nibs.
What am i not understanding here :/
Tnx
viewDidLoad is called for a view controller the first time the view controller's view has been loaded in the view controller's lifecycle.
If you create a new instance of a view controller each time it is presented then you will see viewDidLoad being called once each time it is presented.
If you create a view controller instance and reuse that same instance over and over, then viewDidLoad is only called once (the first time it is presented).
Since it is normal to create new view controller instances each time you need it, viewDidLoad will be called each time you present it.
I have a navigation based application and in the child view I have a button, tapping on which results in calling the popToRootViewController method.
-(IBAction)popToRootViewController
{
[self.navigationController popToRootViewControllerAnimated:YES];
}
This should result in calling the viewWillAppear method of the rootViewController and it is happening in most of the cases. However, occasionally viewDidLoad of rootViewController is called. I am not able to find the reason behind it. Does any one has any idea why viewDidLoad is called sometimes?
On iOS 5 and Earlier, the System May Unload Views When Memory Is Low:
http://developer.apple.com/library/ios/#featuredarticles/ViewControllerPGforiPhoneOS/ViewLoadingandUnloading/ViewLoadingandUnloading.html
viewDidLoad is called once when view controller's view is loaded first time.
viewWillAppear will be called after viewDidLoad method when view controller's view is loaded first time.
Now when ever u push or pop controller in navigationController, the visible controller's viewWillApper method will be called surely.
viewDidLoad, as the name implies, is called just after a view controller has loaded its view. If a view controller is no longer the frontmost controller, it may release its view to save memory (and it used to call viewWillUnload and viewDidUnload which are now deprecated in iOS 6). If this happens, when it comes to front again (or whenever something calls thecontroller.view), it will recreate the view (if is not Nib-based, it will call loadView), and then call viewDidLoad.