swift what init code to I need to write to add a custom init function in a class that derives from a subclass of UIViewController

Question

My project has a:

class BaseViewController: UIViewController

and a:

class PlayerViewController: BaseViewController

I want to add:

    init(player playerObject: Player)

to PlayerViewController. According to my googling, and experimenting, I seem to need to have the following in place.

class BaseViewController: UIViewController {

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

    override init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: NSBundle?) {
        super.init(nibName: nibNameOrNil, bundle: nibBundleOrNil)
    }
}

and

class PlayerViewController: BaseViewController {


    let player: Player!
  
    init(player playerObject: Player)
    {
        self.player = playerObject
        super.init(nibName: nil, bundle: nil)
    }
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

Does this make sense? (It just seemed like a lot of 'extra' code) The code that most feels superflous is the init(coder:) initializer in PlayerViewController.

However if I comment it out, I get the compile error:

'required' initializer 'init(coder:)' must be provided by subclass of 'BaseViewController'

I guess I don't see why it's needed when it's not called by the init(playerObject:) initializer I want to add.

any insite would be appreciated.

Swift

6.9k

Posted by

zespri

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Answer 1

First, I don't know why the SDK makes 'init?(coder:)' required — presumably there's a good reason, which means you just have to live with it.

Second, you shouldn't need to implement either 'init' in BaseViewController, if all you're doing is calling super. According to the Swift rules, if BaseViewController doesn't declare any designated initializers, it inherits all of them from its superclass (UIViewController).

Third, by the same rule, your custom 'init' in PlayerViewController prevents inheritance of designated controllers from its ancestor classes. This is what you want for 'init(nibName:bundle")', because you don't want that to be available for PlayerViewController. It's also what you apparently want for 'init?(coder:)', but unfortunately there's that 'required' … um … requirement. See above under "live with it". Think of it as a legacy from the bad old Objective-C days.

Posted by

QuinceyMorris

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Answer 2

First, I don't know why the SDK makes
init?(coder:)
required …

This is required so that the object can be deserialised from a nib (or storyboard).

In zespri’s example, attempting to instantiate PlayerViewController from a nib will crash with a fatal error, which may or may not be what they want given that the

player

property is implicitly unwrapped.

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Posted by

eskimo

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swift what init code to I need to write to add a custom init function in a class that derives from a subclass of UIViewController

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