I've gotten pretty comfortable using the viewDidLoad method to execute things I want done at the beginning of a view, but reading one of Apple's tutorials they set the data controller for the class in the awakeFromNib method and did nothing in the awakeFromNib. I swapped it and it seemingly worked identically in my app, but I'm not sure if it was better to have it in awakeFromNib or viewDidLoad.
When should I use either one?
awakeFromNib is called when the associated nib file with a class is loaded . Any class that can own a nib can use it. viewDidLoad is used only by view controllers. It is usually called when loading from nib as well but it can also be called by a view created in memory (very rare circumstance.). If you are using controllers, then I would suggest you to use viewDidLoad
For more Refer this Answer
viewDidLoad is associated with the view controller. If you need to initialize another control unarchived from the nib (e.g. UITableViewCell prototype) you cannot overload viewDidLoad, you need to overload awakeFromNib.
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What is the process of a UIViewController birth (which method follows which)?
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I am a new developer, two questions as follows
In controller, why can't I call the awakeFromNib method?
-(void)awakeFromeNib
{
NSLog(#"awakeFromNib");// can't be printed ?
}
Do the methods awakeFromNib and initWithNibName , layoutSubviews have some relations?
When and where should I use them?
- (void)awakeFromNib is only called inside of an object that is being directly loaded from a nib or storyboard. This is usually not a UIViewController.
So, the reason awakeFromNib is not on a view controller is that the view controller is the one that is calling its subviews to awake from the nib as set from the method initWithNibName:bundle:. The layoutSubviews method is also called in a subclass of UIView since a view may have subviews that it needs to layout. If I'm not mistaken, the layoutSubviews on a UIView gets called after awakeFromNib.
Hope this helps!
awakeFromNib is called on the controller after all the connections in it's nib are created and set up.
initWithNibName is the designated initialiser for the class. You call this when you are creating the controller in code.
layoutSubviews is a method that you implement that allows you to give precise layout to subviews.
You should also know about initWithCoder which is the initialiser that is called when the controller is created from a xib file or a storyboard.
Your view controller was likely not awaken from a NIB and instead initialized initWithNibName:bundle:. Only objects that are initialized from a NIB get awakeFromNib.
There is a method that gets called when the view is initialized, either from a NIB or loadView: viewDidLoad
Using viewDidLoad accomplishes pretty much the same thing you'd be expecting from awakeFromNib.
You may be able to use awakeFromNib when your view controller is created from a storyboard, as Abizem suggests, but that will still invoke viewDidLoad immediately afterward.
In my project I am creating UIViewControllers without IB and hence without nib files, so all of the controller content, visible or otherwise, is created programatically in loadView: . Therefore I am essentially "initializing" all my objects in loadView:. Is this the right thing to do? Or should I put all my initialization in initWithNibName:bundle:?
As it is I am creating instances of my UIView subviews in the controller's loadView: like so:
self.mySubView = [[SubView alloc] initWithFrame:aframe];
[self.view addSubView:self.mySubView];
[self.mySubView release];
So I am instantiating several of these subviews using synthesized properties. And as I am not inside an initializer, I am creating these views by calling their accessors as above. But yet, it does feel like this is essentially initialization code and so perhaps I should be calling alloc/ init on my ivars directly and not through accessors, which then leads me to think that I should be doing this in initWithNibName:bundle:.
And if I am right to initialize objects in loadView:, should i really be using an accessor to alloc/ init?
Any thoughts?
At the time initWithNibName:bundle: is called (and here I am assuming you are NOT using a nib file), your view controller's controlled view is not yet created. It get's created the first time self.view is referenced. It is good practice to not do this in the init method. As a result, it follows that it is also good practice to not create your sub views in the init method.
The first time self.view is referenced in any way, the loadView method is automatically called by the view controller. It is your job to programmatically create the controlled view at this time. It is perfectly OK to create your subviews in the loadView method, and if you follow the good practice I suggested, you will need to. But you should only reference self.view in the loadView method for the purpose of assigning the controlled view to it, which means you should only be referencing it exactly once in the loadView method.
You should not be doing this in the loadView method:
[self.view addSubView:self.mySubView];
This is because you are referencing the controlled view while you are in the method that is called to create it. self.view isn't created for you, you have to create it in the 'loadView` method.
Instead, use a local variable to create the controlled view, then assign that local variable to self.view at the end of the loadView method.
simple question,
If you're using a UIStoryboard, will UIViewController call awakeFromNib?
If not, what is the alternative method being called that we should use?
Cheers!
Yes, awakeFromNib will be called when using a UIStoryboard.
While a .storyboard file is a XML document, it will get converted to a set of traditional .nib files when you compile/package your app, so decoding those will be the same as in xib-based projects.
Yes, awakeFromNib is being called.
According to the documentation:
Initializing a View Controller Loaded from a Storyboard When you
create a view controller in a storyboard, the attributes you configure
in Interface Builder are stored in an archive. Later, when the view
controller is instantiated, this archive is loaded into memory and
processed. The result is a set of objects whose attributes match those
you set in Interface Builder. Here’s how that archive is loaded:
If your view controller implements an initWithCoder: method, that
method is called to process the information in the archive. If your
view controller does not implement an initWithCoder: method, your view
controller’s init method is called instead.
After the objects in the archive are loaded, iOS calls the awakeFromNib method on any objects
that implement such a method. You use this method to perform any
configuration steps that require other objects to already be
instantiated.
Yes awakeFromNib will be called when using a UIStoryboard.
I thought that I should never call [super loadView] but something is confusing me.
In description of loadView (UIViewController Class Reference) it is said that "Your custom implementation of this method should not call super.",
but in ZoomingPDFViewer example that they gave, loadView implementation (ZoomingPDFViewerViewController) is calling [super loadView].
I have tried to call it from my loadView method and it works ok, but I just don't understand then what does it mean to not call super.
You definitely should not be calling [super loadView]. I'd say you found a bug in the ZoomingPDFViewer example.
You override loadView when you want to programatically create the view hierarchy for your view controller (not using a xib).
As you pointed out, the docs clearly state that you should not call super.
Your custom implementation of this method should not call super.
I assume this is to avoid loading both from a xib and programatically creating a view as this method is used by the base to load a view from a xib:
If the view controller has an associated nib file, this method loads
the view from the nib file.
Note also that even if during allocation of your UIViewController object you pass nil for the nibNameOrNil parameter that the UIViewController implementation of loadView will try to load any xib with the associated class name in it.
A view controller has an associated nib file if the nibName property
returns a non-nil value, which occurs if the view controller was
instantiated from a storyboard, if you explicitly assigned it a nib
file using the initWithNibName:bundle: method, or if iOS finds a nib
file in the app bundle with a name based on the view controller’s
class name. If the view controller does not have an associated nib
file, this method creates a plain UIView object instead.
The real intent of this method is to give you full control of building the view hierarchy without relying on the built in xib loading mechanism.:
You can override this method in order to create your views manually.
Personally, I override loadView if: 1.) The xib I would make for it is really trivial or 2.) The layout of the control is very dynamic, so creating a xib with a static layout has little benefit.
NSViewController tries to initialize a view from a nib in -loadView. Since your nib name is not set for your controller, it will just give you a self.view = nil; I would assume UIViewController works the same way.
So it should be safe, but you it's completely unnecessary.
If you dont have a view created in your IB, then you should call [super loadView] in your code to give a view to your program.
In case of your custom views, you are suppose to create a view with the interfaz builder, so you dont need to call it.
If you create your ViewController programmatically, you could call super.loadView() instead of self.view = UIView(frame: UIScreen.main.bounds) at the beginning of override func loadView().
However, do NOT call self.view before super.loadView(), since the former will trigger the latter if view did not been loaded.
I don't think it's a good idea to explain Apple's documentation like a robot.
In Programming iOS 4 by Matt Newburg he states:
“To provide a UIViewController with a view manually, implement its
loadView method… You must NOT call super”.
In the iOS 5 Developer's Cookbook by Erica Sadun she states:
“The loadView method allows you to set up the screen and layout any
subviews… Make sure to call [super loadView] whenever you inherit
from a specialized subclass such as UITableViewController or
UITabBarController.”
This, to me at least, is confusing.
Apple is the source of truth and they say NO super call.
If you override this method in order to create your views manually,
you should do so and assign the root view of your hierarchy to the
view property. (The views you create should be unique instances and
should not be shared with any other view controller object.) Your
custom implementation of this method should not call super.
https://developer.apple.com/documentation/uikit/uiviewcontroller/1621454-loadview
[edit]
Another important note scattered around in the UIViewController class reference:
The default loadView method attempts to load the view from the nib
file associated with the view controller (if any).
This is a very old question, but I find that it needs a better answer than the one it got.
Should [super loadView] be called from loadView or not?
It depends. The two sources you cite are talking about different situations, and they're both correct in the context they're describing.
The quote from Neuberg is talking about view controllers that inherit directly from UIViewController. That class has its own implementation of loadView that provides default behavior; specifically, it automatically loads the view hierarchy from a .xib (or storyboard) file that's associated with the view controller. If you call UIViewController's version of that method, the view hierarchy created in that method will either replace your own implementation's view hierarchy, or vice versa. Nine years after this question was posed, the documentation for UIViewController's -loadView method still warns against that:
You can override this method in order to create your views manually. If you choose to do so, assign the root view of your view hierarchy to the view property. The views you create should be unique instances and should not be shared with any other view controller object. Your custom implementation of this method should not call super. [emphasis added]
The quote from Sadun is talking about a different situation, i.e. one in which your view controller is not a direct subclass of UIViewController, but is instead derived from UITableViewController, UITabBarController, etc. Those classes override -loadView themselves and need their versions called. At least in the case of UITableViewController, this is called out in the Overview section:
You may override loadView or any other superclass method, but if you do, be sure to invoke the superclass implementation of the method, usually as the first method call.
So, if you're subclassing UIViewController and providing your own -loadView implementation to generate the controller's views rather than using a .xib or storyboard to provide the views, don't call the superclass's -loadView method. On the other hand, if you're subclassing a class such as UITableView and doing the same thing, check the docs to see whether you need to call that class's -loadView method from your own override.