I am programmatically creating a split view controller using the following code when a table view cell is touched:
let rootViewController: UIViewController = RootTableViewController()
let navVC: UINavigationController = UINavigationController(rootViewController: rootViewController)
let detailViewController: UIViewController = DetailTableViewController()
let splitVC: UISplitViewController = UISplitViewController()
splitVC.viewControllers = [navVC, detailViewController]
self.present(splitVC, animated: true, completion: nil)
but when I tap the tableViewCell I get the error: 'fatal error: unexpectedly found nil while unwrapping an Optional value' which appears to be linked to a UITextField (and all UI Elements) on the RootTableViewController. The first failure is in the viewDidLoad of RootViewController after executing the above code when a value is passed to a ui element
Where exactly does this happen? Wheres the error originated? I had a similar issue where I tried to access IBOutlets before they were created by the system which caused my app to crash.
Specifically I had a UI update function which was called after setting a property of the ViewController.
I got around this by checking for nil in the update function and since it was called before viewDidLoad was called the first time, I called the update function in viewDidLoad manually to make sure that when it shows for the first time, everything is correctly updated.
UPDATE
I think I have an idea of whats going on. You created a Storyboard, setup your UI and chose your ViewControllers as the classes of the ViewControllers in the Storyboard.
If you now want to use the ViewControllers, you have to instantiate them via the Storyboard rather than manually initializing them (something like this):
let storyboard = UIStoryboard(name: "MyStoryboardName", bundle: nil)
let controller = storyboard.instantiateViewController(withIdentifier: "someViewController")
You also could use Segues instead of instantiating something at all. Build your complete UI using the Storyboard and then use a Segue to present the SplitViewController.
The last method I can think of is, that if you want to instantiate the ViewControllers manually and still make use of the Storyboard or a nib, you have to do some custom initialization in in the init functions of your ViewControllers (this code is from a custom view I have in a separate .xib):
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
initializeSubviews()
}
override init(frame: CGRect) {
super.init(frame: frame)
initializeSubviews()
}
func initializeSubviews() {
UINib(nibName: "DatePickerKeyboard", bundle: nil).instantiate(withOwner: self, options: nil)
addSubview(view)
view.frame = self.bounds
}
I'm using Swift 3 to override an init method that initializes my Navigation Controller with a rootviewcontroller (and set the rootviewcontroller delegate to self). But, I'm getting the following error:
Incorrect argument label in call (have 'rootViewController:', expected
'coder:')
class NavigationController: UINavigationController, RootViewControllerDelegate {
let rvc = RootViewController()
convenience init() {
self.init(rootViewController: rvc) // Incorrect argument label in call (have 'rootViewController:', expected 'coder:')
self.rvc.delegate = self
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
}
}
Can somebody explain what I'm doing wrong please? I initially tried using
override func init()
but Xcode ultimately had me convert that to
convenience init()
The init(rootViewController:) is defined in UINavigationController, which is the super class of your NavigationController class. Therefore, you should use super instead of self to refer to it:
init() {
super.init(rootViewController: rvc)
self.rvc.delegate = self
}
Since you have one other initializer defined in NavigationController, Xcode thinks that you were trying to call that initializer. That's why it tells you to put coder: as the argument label.
I'm having issue for writing custom init for subclass of UIViewController, basically I want to pass the dependency through the init method for viewController rather than setting property directly like viewControllerB.property = value
So I made a custom init for my viewController and call super designated init
init(meme: Meme?) {
self.meme = meme
super.init(nibName: nil, bundle: nil)
}
The view controller interface resides in storyboard, I've also make the interface for custom class to be my view controller. And Swift requires to call this init method even if you are not doing anything within this method. Otherwise the compiler will complain...
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
}
The problem is when I try to call my custom init with MyViewController(meme: meme) it doesn't init properties in my viewController at all...
I was trying to debug, I found in my viewController, init(coder aDecoder: NSCoder) get called first, then my custom init get called later. However these two init method return different self memory addresses.
I'm suspecting something wrong with the init for my viewController, and it will always return self with the init?(coder aDecoder: NSCoder), which, has no implementation.
Does anyone know how to make custom init for your viewController correctly ?
Note: my viewController's interface is set up in storyboard
here is my viewController code:
class MemeDetailVC : UIViewController {
var meme : Meme!
#IBOutlet weak var editedImage: UIImageView!
// TODO: incorrect init
init(meme: Meme?) {
self.meme = meme
super.init(nibName: nil, bundle: nil)
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
}
override func viewDidLoad() {
/// setup nav title
title = "Detail Meme"
super.viewDidLoad()
}
override func viewWillAppear(animated: Bool) {
super.viewWillAppear(animated)
editedImage = UIImageView(image: meme.editedImage)
}
}
As it was specified in one of the answers above you can not use both and custom init method and storyboard.
But you still can use a static method to instantiate ViewController from a storyboard and perform additional setup on it.
It will look like this:
class MemeDetailVC : UIViewController {
var meme : Meme!
static func makeMemeDetailVC(meme: Meme) -> MemeDetailVC {
let newViewController = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "IdentifierOfYouViewController") as! MemeDetailVC
newViewController.meme = meme
return newViewController
}
}
Don't forget to specify IdentifierOfYouViewController as view controller identifier in your storyboard. You may also need to change the name of the storyboard in the code above.
You can't use a custom initializer when you initialize from a Storyboard, using init?(coder aDecoder: NSCoder) is how Apple designed the storyboard to initialize a controller. However, there are ways to send data to a UIViewController.
Your view controller's name has detail in it, so I suppose that you get there from a different controller. In this case you can use the prepareForSegue method to send data to the detail (This is Swift 3):
override func prepare(for segue: UIStoryboardSegue, sender: AnyObject?) {
if segue.identifier == "identifier" {
if let controller = segue.destinationViewController as? MemeDetailVC {
controller.meme = "Meme"
}
}
}
I just used a property of type String instead of Meme for testing purposes. Also, make sure that you pass in the correct segue identifier ("identifier" was just a placeholder).
As #Caleb Kleveter has pointed out, we can't use a custom initializer while initialising from a Storyboard.
But, we can solve the problem by using factory/class method which instantiate view controller object from Storyboard and return view controller object.
I think this is a pretty cool way.
Note: This is not an exact answer to question rather a workaround to solve the problem.
Make class method, in MemeDetailVC class, as follows:
// Considering your view controller resides in Main.storyboard and it's identifier is set to "MemeDetailVC"
class func `init`(meme: Meme) -> MemeDetailVC? {
let storyboard = UIStoryboard(name: "Main", bundle: nil)
let vc = storyboard.instantiateViewController(withIdentifier: "MemeDetailVC") as? MemeDetailVC
vc?.meme = meme
return vc
}
Usage:
let memeDetailVC = MemeDetailVC.init(meme: Meme())
One way that I've done this is with a convenience initializer.
class MemeDetailVC : UIViewController {
convenience init(meme: Meme) {
self.init()
self.meme = meme
}
}
Then you initialize your MemeDetailVC with let memeDetailVC = MemeDetailVC(theMeme)
Apple's documentation on initializers is pretty good, but my personal favorite is the Ray Wenderlich: Initialization in Depth tutorial series which should give you plenty of explanation/examples on your various init options and the "proper" way to do things.
EDIT: While you can use a convenience initializer on custom view controllers, everyone is correct in stating that you cannot use custom initializers when initializing from the storyboard or through a storyboard segue.
If your interface is set up in the storyboard and you're creating the controller completely programmatically, then a convenience initializer is probably the easiest way to do what you're trying to do since you don't have to deal with the required init with the NSCoder (which I still don't really understand).
If you're getting your view controller via the storyboard though, then you will need to follow #Caleb Kleveter's answer and cast the view controller into your desired subclass then set the property manually.
There were originally a couple of answers, which were cow voted and deleted even though they were basically correct. The answer is, you can't.
When working from a storyboard definition your view controller instances are all archived. So, to init them it's required that init?(coder... be used. The coder is where all the settings / view information comes from.
So, in this case, it's not possible to also call some other init function with a custom parameter. It should either be set as a property when preparing the segue, or you could ditch segues and load the instances directly from the storyboard and configure them (basically a factory pattern using a storyboard).
In all cases you use the SDK required init function and pass additional parameters afterwards.
Swift 5
You can write custom initializer like this ->
class MyFooClass: UIViewController {
var foo: Foo?
init(with foo: Foo) {
self.foo = foo
super.init(nibName: nil, bundle: nil)
}
public required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
self.foo = nil
}
}
UIViewController class conform to NSCoding protocol which is defined as:
public protocol NSCoding {
public func encode(with aCoder: NSCoder)
public init?(coder aDecoder: NSCoder) // NS_DESIGNATED_INITIALIZER
}
So UIViewController has two designated initializer init?(coder aDecoder: NSCoder) and init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: Bundle?).
Storyborad calls init?(coder aDecoder: NSCoder) directly to init UIViewController and UIView,There is no room for you to pass parameters.
One cumbersome workaround is to use an temporary cache:
class TempCache{
static let sharedInstance = TempCache()
var meme: Meme?
}
TempCache.sharedInstance.meme = meme // call this before init your ViewController
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder);
self.meme = TempCache.sharedInstance.meme
}
As of iOS 13 you can initialize the view controller that resides in a storyboard using:
instantiateViewController(identifier:creator:) method on the UIStoryboard instance.
tutorial:
https://sarunw.com/posts/better-dependency-injection-for-storyboards-in-ios13/
Although we can now do custom init for the default controllers in the storyboard using instantiateInitialViewController(creator:) and for segues including relationship and show.
This capability was added in Xcode 11 and the following is an excerpt from the Xcode 11 Release Notes:
A view controller method annotated with the new #IBSegueAction attribute can be used to create a segue’s destination view controller in code, using a custom initializer with any required values. This makes it possible to use view controllers with non-optional initialization requirements in storyboards. Create a connection from a segue to an #IBSegueAction method on its source view controller. On new OS versions that support Segue Actions, that method will be called and the value it returns will be the destinationViewController of the segue object passed to prepareForSegue:sender:. Multiple #IBSegueAction methods may be defined on a single source view controller, which can alleviate the need to check segue identifier strings in prepareForSegue:sender:. (47091566)
An IBSegueAction method takes up to three parameters: a coder, the sender, and the segue’s identifier. The first parameter is required, and the other parameters can be omitted from your method’s signature if desired. The NSCoder must be passed through to the destination view controller’s initializer, to ensure it’s customized with values configured in storyboard. The method returns a view controller that matches the destination controller type defined in the storyboard, or nil to cause a destination controller to be initialized with the standard init(coder:) method. If you know you don’t need to return nil, the return type can be non-optional.
In Swift, add the #IBSegueAction attribute:
#IBSegueAction
func makeDogController(coder: NSCoder, sender: Any?, segueIdentifier: String?) -> ViewController? {
PetController(
coder: coder,
petName: self.selectedPetName, type: .dog
)
}
In Objective-C, add IBSegueAction in front of the return type:
- (IBSegueAction ViewController *)makeDogController:(NSCoder *)coder
sender:(id)sender
segueIdentifier:(NSString *)segueIdentifier
{
return [PetController initWithCoder:coder
petName:self.selectedPetName
type:#"dog"];
}
In XCode 11/iOS13, you can use
instantiateViewController(identifier:creator:)
also without segues:
let vc = UIStoryboard(name: "StoryBoardName", bundle: nil).instantiateViewController(identifier: "YourViewControllerIdentifier", creator: {
(coder) -> YourViewController? in
return YourViewController(coder: coder, customParameter: "whatever")
})
present(vc, animated: true, completion: nil)
Disclaimer: I do not advocate for this and have not thoroughly tested its resilience, but it is a potential solution I discovered while playing around.
Technically, custom initialization can be achieved while preserving the storyboard-configured interface by initializing the view controller twice: the first time via your custom init, and the second time inside loadView() where you take the view from storyboard.
final class CustomViewController: UIViewController {
#IBOutlet private weak var label: UILabel!
#IBOutlet private weak var textField: UITextField!
private let foo: Foo!
init(someParameter: Foo) {
self.foo = someParameter
super.init(nibName: nil, bundle: nil)
}
override func loadView() {
//Only proceed if we are not the storyboard instance
guard self.nibName == nil else { return super.loadView() }
//Initialize from storyboard
let storyboard = UIStoryboard(name: "Main", bundle: nil)
let storyboardInstance = storyboard.instantiateViewController(withIdentifier: "CustomVC") as! CustomViewController
//Remove view from storyboard instance before assigning to us
let storyboardView = storyboardInstance.view
storyboardInstance.view.removeFromSuperview()
storyboardInstance.view = nil
self.view = storyboardView
//Receive outlet references from storyboard instance
self.label = storyboardInstance.label
self.textField = storyboardInstance.textField
}
required init?(coder: NSCoder) {
//Must set all properties intended for custom init to nil here (or make them `var`s)
self.foo = nil
//Storyboard initialization requires the super implementation
super.init(coder: coder)
}
}
Now elsewhere in your app you can call your custom initializer like CustomViewController(someParameter: foo) and still receive the view configuration from storyboard.
I don't consider this a great solution for several reasons:
Object initialization is duplicated, including any pre-init properties
Parameters passed to the custom init must be stored as optional properties
Adds boilerplate which must be maintained as outlets/properties are changed
Perhaps you can accept these tradeoffs, but use at your own risk.
Correct flow is, call the designated initializer which in this case is the init with nibName,
init(tap: UITapGestureRecognizer)
{
// Initialise the variables here
// Call the designated init of ViewController
super.init(nibName: nil, bundle: nil)
// Call your Viewcontroller custom methods here
}
This solution shows a way to have custom initializers but still be able to use Storyboard WITHOUT using the self.init(nib: nil, bundle: nil) function.
To make it possible to use that, let’s first tweak our MemeDetailsVC to also accept an NSCoder instance as part of its custom initializer, and to then delegate that initializer to super.init(coder:), rather than its nibName equivalent:
class MemeDetailVC : UIViewController {
var meme : Meme!
#IBOutlet weak var editedImage: UIImageView!
init?(meme: Meme, coder: NSCoder) {
self.meme = meme
super.init(coder: aDecoder)
}
#available(*, unavailable, renamed: "init(product:coder:)")
required init?(coder: NSCoder) {
fatalError("Invalid way of decoding this class")
}
override func viewDidLoad() {
title = "Detail Meme"
super.viewDidLoad()
}
override func viewWillAppear(animated: Bool) {
super.viewWillAppear(animated)
editedImage = UIImageView(image: meme.editedImage)
}
}
And then, you instantiate & show the View Controller this way:
guard let viewController = storyboard?.instantiateViewController(
identifier: "MemeDetailVC",
creator: { coder in
MemeDetailVC(meme: meme, coder: coder)
}
) else {
fatalError("Failed to create Product Details VC")
}
//Then you do what you want with the view controller.
present(viewController, sender: self)
// View controller is in Main.storyboard and it has identifier set
Class B
class func customInit(carType:String) -> BViewController
{
let storyboard = UIStoryboard(name: "Main", bundle: nil)
let objClassB = storyboard.instantiateViewController(withIdentifier: "BViewController") as? BViewController
print(carType)
return objClassB!
}
Class A
let objB = customInit(carType:"Any String")
navigationController?.pushViewController(objB,animated: true)
So here's my situation. I am using SWRevealViewController and on the rear VC I have some UI elements that need to be updated when a notification comes through. My problem is that the view may not be visible (and thus isn't loaded) when the notification comes through, so obviously the view hasn't had a chance to register its observers. As a workaround, I tried to instantiate the view controller in my AppDelegate before I post the notification, and originally when I tried this, the IBOutlets were nil. Then I found another question (here) that suggested using the initWithCoder method since this is called when the View Controller is instantiated from the storyboard. However, even using this practice my IBOutlets are still nil. Is there a way to accomplish what I'm trying to do here, or not?
AppDelegate Code (in application:didReceiveRemoteNotification):
let storyboard = UIStoryabord(name: "Main", bundle: nil)
let menuVC = storyboard.instantiaveViewControllerWithIdentifier("menuVC")
NSNotificationCenter.defaultCenter.addObserver(menuVC, selector: "updateMessagesBadge:", name: "notificationName", object: nil)
NSNotificationCenter.defaultCenter.postNotification("notificationName", object: nil)
MenuVC Code:
required init?(coder: aDecoder: NSCoder) {
super.init(coder: aDecoder)
//what to do here?
}
func updateMessagesBadge(notification: NSNotification) {
//try to change outlet properties, but outlets are nil
}
I am trying to initialise a subclass of UIViewController called TestController. I have this swift class:
class TestController : UIViewController {
let testString : String
#IBOutlet weak var test: UITextField!
required init(withString string: String) {
self.testString = string
super.init(nibName: nil, bundle: nil)
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}
I also have a nib file called TestController,
inside it is an instance of UIViewController. The file's owner is none (NSObject in grey) and the class of the UIViewController instance in designer is set in the identity inspector to TestController. There is a UITextField instance as outlet.
The problem is the controller is not initialised from the nib (I think), and the textField outlet is nil.
My goal is to allow initialization of controller's instance from nib programmatically, via the custom initialiser. What am I doing wrong?
You have two problems: First, your nib (or xib) is not created properly (you shouldn't see TestController in interface builder). The easiest way to fix this is to recreate it: New File->Cocoa Touch Class->Create Subclass of UIViewController, and don't forget to check Also Create a XIB file
The second problem is that you're not specifying what nib you want to load. You should specify it in nibName parameter of the initializer:
super.init(nibName: "NewlyCreatedXib", bundle: nil)
When you fix both issues, I believe your code will work properly.