tested with XCode 7.1.1, Swift 2.1 & iOS 9
You have a few options to save your (array of) custom objects :
- NSUserDefaults : to store app settings, preferences, user defaults :-)
- NSKeyedArchiver : for general data storage
- Core data : for more complex data storage (database like)
I leave Core data out of this discussion, but want to show you why you should better use NSKeyedArchiver over NSUserdefaults.
I've updated your Player class and provided methods for both options. Although both options work, if you compare the 'load & save' methods you'll see that NSKeydArchiver requires less code to handle arrays of custom objects. Also with NSKeyedArchiver you can easily store things into separate files, rather than needing to worry about unique 'key' names for each property.
import UIKit
import Foundation
// a custom class like the one that you want to archive needs to conform to NSCoding, so it can encode and decode itself and its properties when it's asked for by the archiver (NSKeydedArchiver or NSUserDefaults)
// because of that, the class also needs to subclass NSObject
class Player: NSObject, NSCoding {
var name: String = ""
// designated initializer
init(name: String) {
print("designated initializer")
self.name = name
super.init()
}
// MARK: - Conform to NSCoding
func encodeWithCoder(aCoder: NSCoder) {
print("encodeWithCoder")
aCoder.encodeObject(name, forKey: "name")
}
// since we inherit from NSObject, we're not a final class -> therefore this initializer must be declared as 'required'
// it also must be declared as a 'convenience' initializer, because we still have a designated initializer as well
required convenience init?(coder aDecoder: NSCoder) {
print("decodeWithCoder")
guard let unarchivedName = aDecoder.decodeObjectForKey("name") as? String
else {
return nil
}
// now (we must) call the designated initializer
self.init(name: unarchivedName)
}
// MARK: - Archiving & Unarchiving using NSUserDefaults
class func savePlayersToUserDefaults(players: [Player]) {
// first we need to convert our array of custom Player objects to a NSData blob, as NSUserDefaults cannot handle arrays of custom objects. It is limited to NSString, NSNumber, NSDate, NSArray, NSData. There are also some convenience methods like setBool, setInteger, ... but of course no convenience method for a custom object
// note that NSKeyedArchiver will iterate over the 'players' array. So 'encodeWithCoder' will be called for each object in the array (see the print statements)
let dataBlob = NSKeyedArchiver.archivedDataWithRootObject(players)
// now we store the NSData blob in the user defaults
NSUserDefaults.standardUserDefaults().setObject(dataBlob, forKey: "PlayersInUserDefaults")
// make sure we save/sync before loading again
NSUserDefaults.standardUserDefaults().synchronize()
}
class func loadPlayersFromUserDefaults() -> [Player]? {
// now do everything in reverse :
//
// - first get the NSData blob back from the user defaults.
// - then try to convert it to an NSData blob (this is the 'as? NSData' part in the first guard statement)
// - then use the NSKeydedUnarchiver to decode each custom object in the NSData array. This again will generate a call to 'init?(coder aDecoder)' for each element in the array
// - and when that succeeded try to convert this [NSData] array to an [Player]
guard let decodedNSDataBlob = NSUserDefaults.standardUserDefaults().objectForKey("PlayersInUserDefaults") as? NSData,
let loadedPlayersFromUserDefault = NSKeyedUnarchiver.unarchiveObjectWithData(decodedNSDataBlob) as? [Player]
else {
return nil
}
return loadedPlayersFromUserDefault
}
// MARK: - Archivig & Unarchiving using a regular file (using NSKeyedUnarchiver)
private class func getFileURL() -> NSURL {
// construct a URL for a file named 'Players' in the DocumentDirectory
let documentsDirectory = NSFileManager().URLsForDirectory((.DocumentDirectory), inDomains: .UserDomainMask).first!
let archiveURL = documentsDirectory.URLByAppendingPathComponent("Players")
return archiveURL
}
class func savePlayersToDisk(players: [Player]) {
let success = NSKeyedArchiver.archiveRootObject(players, toFile: Player.getFileURL().path!)
if !success {
print("failed to save") // you could return the error here to the caller
}
}
class func loadPlayersFromDisk() -> [Player]? {
return NSKeyedUnarchiver.unarchiveObjectWithFile(Player.getFileURL().path!) as? [Player]
}
}
I've tested this class as follows (single view app, in the viewDidLoad method of the ViewController)
import UIKit
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
// create some data
let player1 = Player(name: "John")
let player2 = Player(name: "Patrick")
let playersArray = [player1, player2]
print("--- NSUserDefaults demo ---")
Player.savePlayersToUserDefaults(playersArray)
if let retreivedPlayers = Player.loadPlayersFromUserDefaults() {
print("loaded \(retreivedPlayers.count) players from NSUserDefaults")
print("\(retreivedPlayers[0].name)")
print("\(retreivedPlayers[1].name)")
} else {
print("failed")
}
print("--- file demo ---")
Player.savePlayersToDisk(playersArray)
if let retreivedPlayers = Player.loadPlayersFromDisk() {
print("loaded \(retreivedPlayers.count) players from disk")
print("\(retreivedPlayers[0].name)")
print("\(retreivedPlayers[1].name)")
} else {
print("failed")
}
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
}
as said above, both methods produce the same result
Also in a real life application you could do better error handling in the, as archiving & unarchiving could fail.
