A normal answer would be, when the view will appear.
Say I have a UIViewController. Let's call that vc.
Say I want vc to control a view.
so I do vc.view = controlledView;
I expect everytime controlledView is about to appear then [vc viewWillAppear] will be called.
It doesn't.
What's wrong?
Also viewDidLoad is also not called even after I do
[vc view]
Technically, vc.view is already loaded
if you are calling viewWillAppear in any other file , with other View instance then it will never call.
viewWillAppear method calls every time when go to that view and if you leave it and then again come or come-back , it will call again.
please must use 'Super' keyword as.
[super viewWillAppear] in WillAppear method.
According to docs
This method is called before the receiver’s view is about to be added
to a view hierarchy and before any animations are configured for
showing the view. You can override this method to perform custom tasks
associated with displaying the view.
viewWillAppear is always called when your view is about to appear, as name itself suggests.
If a view controller is presented by a view controller inside of a popover, this method is not invoked on the presenting view controller after the presented controller is dismissed.
Life Cycle of view controller goes like this:
When a viewcontroller is allocated and loaded, loadView is called then viewDidLoad is called. You can see the entire flow as in image.
Refer to this image
NOTE: This image is taken from this answer
The right answer is the following.
Did you add the child viewController as the child of the parent child view controller.
viewWillAppear will only be called for the parent view controller (the top screen view controller) unless the other viewController is declared as the child.
Then the parentViewController will pass on viewWillAppear events.
Related
If I wanted to perform some sort of action right after dismissing a modal view controller, where exactly would I put the code? I know it wouldn't be in viewDidLoad because the rootviewcontroller was already loaded into memory (because it was just temporarily hidden by the modal view) and I'm not sure about viewWillAppear or viewDidAppear because of course the view has already been loaded into memory.
ViewWillAppear will be called again in caller view controller when modal is dismissed, so with some logic can be a good place.
Otherwise you can think about implementing a delegate, or if synchronicity is not an option to be considered, you can send a custom NSNotification to be catched by the modal caller.
I understand that viewWillAppear will be called when duh.... when the the view is about to appear.
But how does IOS know that a controller's view is about to appear?
When exactly that and how it is implemented?
For example, does the childController.view check first that window is one of it's super ancestors? Does the view has a pointer to it's controller? How exactly that works? Does everytime a view is added it check whether it's window is it's super ancestor and whether it is the view outlet of a UIViewController?
For example, if I add childcontroller.view but not to a subview of any view that's being called. Will viewWillAppear called?
Does the childController need to be the a child of a parentController so that viewWillAppear of the childController will be called when the parentController's viewWillAppear is called automatically?
The view is loaded by your controller using the - (void)loadView method. This method is implemented to load a blank view or a view from a nib/storyboard. You only need to override it if you really need to create a view hierarchy from scratch.
All of the magic happens when the value of the view property is first requested and the controller detects the value is nil. All of the life cycle method calls are handled by the UIViewController. There is nothing you need to do other than implement the methods if you need them. Remember one thing: There is no guarantee the view has been loaded until the - (void)viewDidLoad method has been called.
Everything I've learned about controllers how they work has come from the View Controller Programming Guide.
How does iOs know?
Does each view has a pointer to it's controller?
What happened?
When we pop a viewController from navigation, does the navigationController arrange which view should be called?
For example:
If I added:
[[BNUtilitiesQuick window] addSubview:[BNUtilitiesQuick searchController].view];
viewWillAppear will be called.
ios does know which viewControler viewwillappear should be called even under cases in the question. There is no way I can think of how they know that without a pointer from view to viewcontroller.
However, window doesn't know the viewController. I am passing the view outlet of the controller not the controller. How can iOs 5 knows that it has to call [[BNUtilitiesQuick searchController] viewWillAppear:YES]
Navigation Controller maintains a stack of view controllers.
Once a view controller is popped, it is removed from the stack, and now the view controller exactly below this is the first view controller.This is how it works.
You can check documentation for more details - http://developer.apple.com/library/ios/#featuredarticles/ViewControllerPGforiPhoneOS/Introduction/Introduction.html#//apple_ref/doc/uid/TP40007457
http://developer.apple.com/library/ios/#documentation/WindowsViews/Conceptual/ViewControllerCatalog/Chapters/NavigationControllers.html#//apple_ref/doc/uid/TP40011313-CH2
I have a bunch of pages I am chaining together and presenting as modal view controllers. THey all have viewDidLoad methods. It seems that when one is loaded though it calls the viewDidLoad methods of ones in the background too. How can I stop this? Thanks!
You can't. The viewDidLoad method will get called when the view is loaded. Asking a view controller for its view loads the view.
Consider moving code into your viewWillAppear:(BOOL)animated method. That way it will only get called before the view is actually shown to the user.
Does the addSubview method actually load the view into the application or not? The reason I am asking is because I have two two views in my application. The application delegate adds the two views as subviews and then brings one of the views up front. Now, I have a print statement in each of the viewDidLoad methods for each view. When I run the application, the application delegate loads the views as subViews and as each view is loaded, I actually see the console print out the statements that I placed in each of the viewDidLoad methods. Is this supposed to be doing this?
viewDidLoad is actually a method of UIViewController, not UIView. It gets called after the view gets loaded into memory (after your init method, but before the awakeFromNib). You'll notice that addSubview: takes a UIView as a parameter, so the view must have been loaded in order for the view to be added to another view. Otherwise you'd be trying to add an imaginary view.
In answer to your question, yes it is supposed to be doing this. viewDidLoad is called long before you addSubview. In fact, if you take out the addSubview: lines, you'll notice that it's still getting called (because you're creating the view's controller).
My understanding is that views are lazily loaded. If your viewcontroller has 10 view, they are not all loaded until you actually try to access them.