Converting [NSURL] into [String] for NSUserDefaults? - swift

Question

I'm saving images into Parse Data as an array of NSURL's. Once I have them back into my app I would like to convert them to [String] so my app can temporarily store them. Any ideas?
Here is my code....
// Saving like This....
vc.videoImageArry = defaults.setObjectForKey("vidImages)
//Retrieving like This....
vc.vidImageArray = defaults.objectForKey("vidImages") as! [NSURL]

Answer 1

Using NSData
You can convert each NSURL to NSData in order to save it
func save(urls: [NSURL]) {
let urlsData = urls.map { $0.dataRepresentation }
NSUserDefaults.standardUserDefaults().setObject(urlsData, forKey: "urlsData")
}
Later on you can retrieve the NSData array and convert it back to [NSURL]
func load() -> [NSURL]? {
let retrievedData = NSUserDefaults.standardUserDefaults().arrayForKey("urlsData") as? [NSData]
return retrievedData?.map { NSURL(dataRepresentation: $0, relativeToURL: nil) }
}
Using String
Alternatively you can save the urls as String(s)
func save(urls: [NSURL]) {
let urlsData = urls.map { $0.absoluteString }
NSUserDefaults.standardUserDefaults().setObject(urlsData, forKey: "urlsData")
}
func load() -> [NSURL?]? {
let retrievedData = NSUserDefaults.standardUserDefaults().arrayForKey("urlsData") as? [String]
return retrievedData?.map { NSURL(string: $0) }
}
As discussed in the comments below, if data is written to NSUserDefaults exclusively with the save function, we know that every element of the array is a String representing a valid NSURL.
So we can change the return type of load from [NSURL?]? to [NSURL]? using this alternate version of load.
func load() -> [NSURL]? {
let retrievedData = NSUserDefaults.standardUserDefaults().arrayForKey("urlsData") as? [String]
return retrievedData?.flatMap { NSURL(string: $0) }
}

Answer 2

To convert from NSURL to String:
String(url)
To convert from String to NSURL:
NSURL(string: string)
Here's a fully working example that converts an array both ways:
import Cocoa
let urls = [NSURL(string: "http://www.swift.org/")!, NSURL(string: "http://www.apple.com/")!]
let strings = urls.map { String($0) }
let backToUrls = strings.map { NSURL(string: $0)! }
I believe that the above answers your specific question.
Having said that, the line for saving doesn't look right to me. You may want to look further into NSUserDefaults or ask a separate question if you're having difficulty with that line. You would need to paste some more context like lines above and below and exact error messages you're getting if any.