How do you perform optional binding on an optional of optional?

Question

How do you do optional binding on an optional of optional?

For example, assume UIViewController's navigationController property is an optional of optional. Should I use method #1 or method #2, or is there a third way?

Method #1

if let navigationController = viewController.navigationController! {

}

or

Method #2

if let optionalNavigationController = viewController.navigationController {
   let navigationController = optionalNavigationController {

    }
}

Related: [How to unwrap Optional> in Swift 1.2](http://stackoverflow.com/questions/28724946/how-to-unwrap-optionaloptionalt-in-swift-1-2). — Martin R, Aug 06 '15 at 12:17

score 1 · Answer 1 · answered Aug 06 '15 at 12:04

1

There is another solution:

if let stillOptional = viewController.navigationController, let notOptional = stillOptional {
    //use notOptional here
}

answered Aug 06 '15 at 12:04

Dániel Nagy

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Method #1 I listed seems cleaner since it's only one level? – Boon Aug 06 '15 at 12:19
1

@Boon it is cleaner, but if `navigationController` is `nil`, it will crash because of the forced unwrapping. – Dániel Nagy Aug 06 '15 at 12:20

score 0 · Answer 2 · answered Aug 06 '15 at 12:05

0

if let navigationController = viewController?.navigationController

answered Aug 06 '15 at 12:05

oisdk

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Why optional on viewController? – Boon Aug 06 '15 at 12:09
[Optional chaining](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/OptionalChaining.html) – oisdk Aug 06 '15 at 12:11
ViewController is not an optional in this case, why chain it? – Boon Aug 06 '15 at 12:15
Oh, sorry. I was confused. – oisdk Aug 06 '15 at 12:24

score 0 · Answer 3 · answered Aug 06 '15 at 12:08

0

Much more functional-programming solution:

if let a = optionalOfOptional?.map({$0}) {
    println(a)
}

answered Aug 06 '15 at 12:08

rshev

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score 0 · Answer 4 · answered Aug 06 '15 at 12:11

If you know that the view controller has a navigation controller, because you designed it in Interface Builder or created it programmatically, declare a variable

var navigationController : UINavigationController!

and assign the navigation controller in viewDidLoad() as implicit unwrapped optional

navigationController = viewController!.navigationController!

If you don't know, use a normal optional binding as described in the other answers

How do you perform optional binding on an optional of optional?

4 Answers4