Swift - if string is nil. don't add it to the array

I have an Array of Image links -

Array

Image

let alamofireSource = [AlamofireSource(urlString: Img1!)!, AlamofireSource(urlString: Img2!)!,
AlamofireSource(urlString: Img3!)!, AlamofireSource(urlString: Img4!)!]
slideshow.setImageInputs(alamofireSource)


some posts have only one image or two or three, and so on. so, sometimes image 2 (for example) is nil, In that case, I don't want it to be added to the array, is that possible?

3 Answers
3

You can try ( Swift 4 )

let arr = [img1,img2].compactMap{$0}.map{AlamofireSource(urlString:$0)!}


or

let arr = alamofireSource.compactMap{$0}


for Swift 3

let arr = alamofireSource.flatMap{$0}


AlamofireSource(urlString:)

Img1

Img4

so, sometimes image 2 (for example) is nil, In that case, I don't want
it to be added to the array, is that possible?

Yes it is. Although I would go with Sh_Khan's suggestion to use the compactMap method to achieve it, but it would be useless for your current case:

compactMap

Based on your code snippet, I'd assume that alamofireSource of type [AlamofireSource], but not [AlamofireSource?] and that's because you are forcibly unwrap its elements (by adding ! to each of its elements). So far alamofireSource doesn't contain nils (actually it could be more danger than just a declaration, your app might crash!)

alamofireSource

[AlamofireSource]

[AlamofireSource?]

!

alamofireSource

So first of all, I would recommend to remove the ! from alamofireSource:

!

alamofireSource

let alamofireSource = [AlamofireSource(urlString: Img1!),
AlamofireSource(urlString: Img2!),
AlamofireSource(urlString: Img3!),
AlamofireSource(urlString: Img4!)]


which means let it be as [AlamofireSource?], therefore you would gain the benefit of using compactMap(_:):

[AlamofireSource?]

compactMap(_:)

Returns an array containing the non-nil results of calling the given
transformation with each element of this sequence.

As:

let alamofireSourceWihoutNils = alamofireSource.compactMap { $0 }


Assuming you put your Optional url strings into an array, say urlStrings (of type [String?]), you can construct alamofireSource according to (Swift 4):

Optional

urlStrings

[String?]

alamofireSource

let alamofireSource = urlStrings.compactMap { $0.map(AlamofireSource.init) }


Which make use of the map(_:) operator of Optional and compactMap(_:) to unwrap the two-level optionality.

map(_:)

Optional

compactMap(_:)

Details

Your example contains two levels of optionality:

ImgX

String?

img1

img4

CapitalFirstLetter

init?(urlString: String, placeholder: UIImage? = nil)

AlamofireSource

First of all, lets gather the optional image links (imgX) into an array

imgX

let urlStrings = [url1, url2, url3, url4] // [String?]


You can combine the map(_:) operator of Optional with compactMap(_:) to safely unwrap and make use of the .some entires of urlStrings, thereafter collect the successful invocations of the failable initializer of AlamofireSource:

map(_:)

Optional

compactMap(_:)

.some

urlStrings

AlamofireSource

let alamofireSource = urlStrings.compactMap { $0.map(AlamofireSource.init) }

// or, use a named closure argument
let alamofireSource = urlStrings.compactMap { str in str.map(AlamofireSource.init) }


If using Swift 3, replace the compactMap(_:) invocation above with flatMap(_:):

compactMap(_:)

flatMap(_:)

let alamofireSource = urlStrings.flatMap { $0.map(AlamofireSource.init) }

// or, use a named closure argument
let alamofireSource = urlStrings.flatMap { str in str.map(AlamofireSource.init) }


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