Unexpectedly found nil while unwrapping an Optional value - swift

Question

Probably I don't understand clearly Optional values:
class func albumsWithJSON(allResults: NSArray) -> [Album] {
var albums = [Album]()
if allResults.count>0 {
for result in allResults {
var name = result["trackName"] as? String
if name == nil {
name = result["collectionName"] as? String
}
var price = result["formattedPrice"] as? String
if price == nil {
price = result["collectionPrice"] as? String
if price == nil {
var priceFloat: Float? = result["collectionPrice"] as? Float
var nf: NSNumberFormatter = NSNumberFormatter()
nf.maximumFractionDigits = 2;
if priceFloat != nil {
price = "$"+nf.stringFromNumber(priceFloat)
}
}
}
let thumbnailURL = result["artworkUrl60"] as String
let imageURL = result["artworkUrl100"] as String
let artistURL = result["artistViewUrl"] as? String
var itemURL = result["collectionViewUrl"] as? String
if itemURL == nil {
itemURL = result["trackViewUrl"] as? String
}
var newAlbum = Album(name: name!, price: price!, thumbnailImageURL: thumbnailURL, largeImageURL: imageURL, itemURL: itemURL!, artistURL: artistURL!)
albums.append(newAlbum)
}
}
}
At this line I get "unexpectedly found nil while unwrapping an Optional value" error:
var newAlbum = Album(name: name!, price: price!, thumbnailImageURL: thumbnailURL, largeImageURL: imageURL, itemURL: itemURL!, artistURL: artistURL!)
Obviously some informations are missing from JSON, but how can I handle a missing value?

Answer 1

All that error means is that one of the values that you're passing into that function is nil. When you put the ! at the end of those values, it unwraps it. If the value is nil while unwrapping, it throws an exception.
The way to fix this is dependent on how important the values being nil is. If you cannot live with any one of those being nil, then you'll have to check for nil and do something. If you can have them be nil, then you'll want to make sure that the function accepts nil values.
To better understand optionals, you should read the docs: https://developer.apple.com/library/prerelease/mac/documentation/Swift/Conceptual/Swift_Programming_Language/TheBasics.html#//apple_ref/doc/uid/TP40014097-CH5-XID_483