Best Practice using an Array of Strings with NSUserDefault - arrays

Question

I'm having a bit trouble saving an array of strings to userDefaults. I have an Array of strings declaired in a class, with a property observer ment to sync to userDefaults. Furthermore, I want the array to be limited to a maximum of 5 Strings.
let userDefaults = NSUserDefaults.standardUserDefaults()
var suggestions: [String]! {
didSet {
var arrayEnd = suggestions.count
if arrayEnd >= 5 {
arrayEnd = 4
}
let newArray = Array(suggestions[0...arrayEnd])
userDefaults.setObject(newArray, forKey: "suggestions")
userDefaults.synchronize()
}
}
func getSuggestionData() {
if userDefaults.valueForKey("suggestions") != nil {
self.suggestions = userDefaults.valueForKey("suggestions") as? [String]
}
}
override func viewDidLoad() {
super.viewDidLoad()
getSuggestionData()
suggestions.insert("someString", atIndex: 0)
}
}
When i run this i get:
fatal error: unexpectedly found nil while unwrapping an Optional value
on the line where I try to insert a new object to the array.
I have tried following the approach in this thread, but it didn't save anything to the list.
I'm new to swift, and optional-types aren't my strong side, maybe someone know what's wrong?

Answer 1

As reading from user defaults could return nil values, use optional binding to be safe:
func getSuggestionData() {
if let suggestionArray = userDefaults.objectForKey("suggestions") {
self.suggestions = suggestionArray
} else {
self.suggestions = [String]()
}
}
But I'd recommend to use an non-optional variable with a defined default value.
In AppDelegate of your app, override init() or insert the code to register the key/value pair.
override init()
{
let defaults = NSUserDefaults.standardUserDefaults()
let defaultValue = ["suggestions" : [String]()];
defaults.registerDefaults(defaultValue)
super.init()
}
Registering the default keys and values is the way Apple suggests in the documentation.
If no value is written yet, the default value (empty array) is read.
If there is a value, the actual value is read
Instead of the value observer of the variable suggestions implement a method to insert a new value, delete the last one and write the array to disk.
There is no need to use optional binding because the array in user defaults has always a defined state.
let userDefaults = NSUserDefaults.standardUserDefaults()
var suggestions = [String]()
func insertSuggestion(suggestion : String)
{
if suggestions.count == 5 { suggestions.removeLast() }
suggestions.insert(suggestion, atIndex: 0)
userDefaults.setObject(suggestions, forKey: "suggestions")
userDefaults.synchronize()
}
func getSuggestionData() {
suggestions = userDefaults.objectForKey("suggestions") as! [String]
}
override func viewDidLoad() {
super.viewDidLoad()
getSuggestionData()
insertSuggestion("someString")
}
A side note:
never use valueForKey: rather than objectForKey: if you don't need explicitly the key-value-coding method.

Answer 2

Hey Just try like this way.
var suggestions: [String] = Array() {
didSet {
var arrayEnd = suggestions.count
if arrayEnd >= 5 {
arrayEnd = 4
}
if arrayEnd > 0
{
let newArray = Array(suggestions[0...(arrayEnd-1)])
userDefaults.setObject(newArray, forKey: "suggestions")
userDefaults.synchronize()
}
}
}
func getSuggestionData() {
if userDefaults.valueForKey("suggestions") != nil {
self.suggestions = userDefaults.objectForKey("suggestions") as! Array
}
}
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
getSuggestionData()
if self.suggestions.count > 4
{
var str = "\(self.suggestions.count)"
self.suggestions.insert(str, atIndex: self.suggestions.count)
}
}