在 Swift 中为 UIViewController 定制初始化，在情节串连板中设置接口

我在为 UIViewController 的子类编写自定义 init 时遇到了问题，基本上我想通过 viewController 的 init 方法传递依赖关系，而不是像 viewControllerB.property = value那样直接设置属性

因此，我为 viewController 创建了一个自定义 init，并且调用 super 设定 init

init(meme: Meme?) {
self.meme = meme
super.init(nibName: nil, bundle: nil)
}

视图控制器接口位于情节串连板中，我还将自定义类的接口作为我的视图控制器。Swift 需要调用这个 init 方法，即使您没有在这个方法中做任何事情。否则编译器会抱怨..。

required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
}

问题是，当我尝试用 MyViewController(meme: meme)调用我的自定义 init 时，它根本不会在 viewController 中调用 init 属性..。

我试图调试，我发现在我的 viewController 中，首先调用 init(coder aDecoder: NSCoder)，然后调用我的自定义 init。但是这两个 init 方法返回不同的 self内存地址。

我怀疑 viewController 的 init 出了问题，它总是返回 self和 init?(coder aDecoder: NSCoder)，而 init?(coder aDecoder: NSCoder)没有实现。

有人知道如何正确地为 viewController 定制 init 吗？ 注意: 我的 viewController 的接口是在故事板中设置的

这是我的 viewController 代码:

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)
}


}
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小开

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.

小开

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
}
小开

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).

小开

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.

小开

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.

小开

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())
小开

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
}
}
小开

// 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)
小开

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.

小开

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"];
}
小开

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/

小开

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


}
小开

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)
小开

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)

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