My iOS 5 project uses storyboards. I have a view whose view controller inherits from a class that in turn inherits from UIViewController. This class belongs to a framework that was written for non-storyboard projects, i.e. it initialises the view by overriding loadView. When my view controller runs, it receives self.view as set up by the super class, thus rendering ineffective the Interface Builder settings for the current view.
While I do have the source code of the framework I'm using, and in theory could edit it to remove the loadView override and relocate the code to viewDidLoad for example, I'm wondering if there is a better way to do this just from my own code. Basically I would need to have my [super loadView] un-overriden, or bypass it by calling my superclass's superclass's (i.e. UIViewController) loadView. Is there any way to achieve this?
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In a project I'm working on, I have a view controller which overrides the loadView() method for setting up the view hierarchy programatically. I was curious if there are requirements regarding what goes in this method versus in viewDidLoad(), or if the latter is redundant when loadView() is already overridden. Is there anything that cannot be done e.g. at the very end of loadView() that should be deferred until viewDidLoad() is called, or is it simply a matter of preference?
EDIT: The initial phrasing of this question was somewhat opinion based. To clarify, I'm interested in whether there is any reference material indicating that there are technical limitations regarding methods that are not able to be used in loadView() that can be used in viewDidLoad().
The documentation for loadView pretty much answers your question:
If you use Interface Builder to create your views and initialize the view controller, you must not override this method.
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.
If you want to perform any additional initialization of your views, do so in the viewDidLoad() method.
In other words, only ever override loadView if you are writing your view controller strictly in code - no nib or storyboard. And then only if you have a reason for the base view of the controller to be something other than a plain old UIView that you get by default. And remember that you must not call super.loadView() in your implementation.
I would use viewDidLoad to create and setup any subviews you wish to add to the base view of the view controller (whether loadView was used or not). Also use viewDidLoad for any other setup that can't be done until the view has been loaded.
Technically, if you override loadView to setup a custom base view, anything you might have put in viewDidLoad can be put in your loadView. But I would still separate the responsibility. Only use loadView (if needed) to create and setup the base view of the controller. Use viewDidLoad to create other subviews as needed and any other controller setup.
Also keep in mind that some view controller initial setup belongs in the initializer. But such code can't make any reference to any views.
I am new to iOS development. So pardon me if this is a very basic thing.
From what I have learnt till now:
UIViewController class resembles somewhat equivalent to an Activity class in Android.
and viewDidLoad/viewWillAppear method to onCreate/onStart method
and viewDidAppear method to onResume method
Please correct me if I am wrong here.
Now, in Android we can monitor which of these methods(including other lifecycle methods) are triggered/called by implementing an Interface (ActivityLifecycleCallbacks) (somewhat resembling a protocol in iOS) which exists in the Application class in any Activity (particularly in a class which extends Application class).
It means that now these methods will be triggered/called whenever there is any navigation from one screen to another in the android app.
How do I do this in iOS using Swift? How do I know which screen(UIViewcontroller) the user is currently in and where he is navigating?
In short I want to write a standalone class which logs which screen(UIViewController) the user is currently in and which one of the lifecycle methods(viewDidLoad, viewWillAppear etc) is being executed?
Someone please help me out.
Edit:- I don't want them to subclass my standalone class instead of UIViewController class.
There are no global events that are fired when the UIViewController lifecycle methods are called. To create those you would need to subclass UIViewController as has been suggested.
You can look at UIApplication.sharedApplication().keyWindow?.rootViewController to get the current root view controller (which is often, but not always the currently active view controller).
You wouldn't typically design an app that depended on some central object tracking the state of view controllers.
The flow of UIViewController methods is pretty well described in the class reference and you can also work it out from the function names -
viewDidLoad called after the view controller instance is loaded (once per instantiation)
viewWillAppear called before this view appears
viewDidAppear called after this view appears
viewWillDisappear called before this view disappears
viewDidDisappear called after this view disappears
Create a view controller subclass and add that implementation in there. Then make sure all the view controllers you create subclass that new class rather than UIViewController itself
I want to break my code into 3 files and them up via addsubview. For ex. i have a masterview, mastreview contains a currentView. CurrentView contains 1 webview and 1 tableview.
Now, i have written all code in one file and it works like a charm. But i want to make it abstract and loosely coupled . So i need a separate file ex. webviewController to implement its delegate and function related to it AND tableviewController to implement its delegate and functions related to it. And add both by addsubview, alloc init in masterview file.
I did it my way,though i was able to addsubview on CurrentView, the problem was my delegate functions are not working properly.
Also, i am confused about tableviewController should inherit UIViewController or UIView or UITableView.
it would be good if anyone can guide or send some link related to it, any example...???
Actually you should have the app crashing if the delegates are not retained somewhere.
If you do link the object with view controller to be it's delegate at Interface Builder, the view controller will be destroyed after it's outlets so you don't care. If you are creating separate class for the delegate, you should care about it's lifecycle, standard classes do not retain their delegates so you have to retain it on the same level where you are retaining the delegated object. Like if you are creating a UITableView subview and you have MyTVDelegate class, you should create the delegate instance, assign it to tableView.delegate and retain as viewController var so that viewController will dealloc both subviews and their delegates when needed.
For the second question, UITableviewController inherits UIViewController as you can see at header files (command+click on UITableviewController), and UITableView inherits UIView. Every viewcontroller should have the root view of UIView and I believe UITableviewController has UITableView as it's root view.
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.