How can I store an array of custom objects (Goals)

Question

How can I store an array of objects of type Goal which I have created in NSUserDefaults? (in swift)

Here is the code:

func saveGoalList ( newGoalList         


        

Answer 1

For Swift 2.1, your Goal class should look like :

import Foundation

class Goal : NSObject, NSCoding {

    var title: String

    // designated initializer
    init(title: String) {
        self.title = title

        super.init()        // call NSObject's init method
    }

    // MARK: - comply wiht NSCoding protocol

    func encodeWithCoder(aCoder: NSCoder) {
        aCoder.encodeObject(title, forKey: "GoalTitle")
    }

    required convenience init?(coder aDecoder: NSCoder) {
        // decoding could fail, for example when no Blog was saved before calling decode
        guard let unarchivedGoalTitle = aDecoder.decodeObjectForKey("GoalTitle") as? String
            else {
                // option 1 : return an default Blog
                self.init(title: "unknown")
                return

                // option 2 : return nil, and handle the error at higher level
        }

        // convenience init must call the designated init
        self.init(title: unarchivedGoalTitle)
    }
}

and you should use it in your view controller like I did in this test code :

    // create an array with test data
    let goal1 = Goal(title: "first goal")
    let goal2 = Goal(title: "second goal")
    let goalArray = [goal1, goal2]

    // first convert the array of custom Goal objects to a NSData blob, as NSUserDefaults cannot handle arrays of custom objects directly
    let dataBlob = NSKeyedArchiver.archivedDataWithRootObject(goalArray)

    // this NSData object can now be stored in the user defaults
    NSUserDefaults.standardUserDefaults().setObject(dataBlob, forKey: "myGoals")

    // sync to make sure they are saved before we retreive anytying
    NSUserDefaults.standardUserDefaults().synchronize()

    // now read back
    if let decodedNSDataBlob = NSUserDefaults.standardUserDefaults().objectForKey("myGoals") as? NSData {
        if let loadedGoalsArray = NSKeyedUnarchiver.unarchiveObjectWithData(decodedNSDataBlob) as? [Goal] {
            for goal in loadedGoalsArray {
                print("goal : \(goal.title)")
            }
        }
    }

As a final remark : it would be easier to use NSKeyedArchiver instead of NSUserDefaults, and store your array of custom objects directly to a file. You can read more about the difference between both methods in another answer I posted here.

Answer 2

I am posting code from a learning project I did to store objects using NSCoding. Fully functional and ready to use. A math game that was storing game variables, etc.

//********This class creates the object and properties to store********
import Foundation
class ButtonStates: NSObject {

    var sign: String = "+"
    var level: Int = 1
    var problems: Int = 10
    var time: Int = 30
    var skipWrongAnswers = true

    func encodeWithCoder(aCoder: NSCoder!) {
        aCoder.encodeObject(sign, forKey: "sign")
        aCoder.encodeInteger(level, forKey: "level")
        aCoder.encodeInteger(problems, forKey: "problems")
        aCoder.encodeInteger(time, forKey: "time")
        aCoder.encodeBool(skipWrongAnswers, forKey: "skipWrongAnswers")
    }

    init(coder aDecoder: NSCoder!) {
        sign = aDecoder.decodeObjectForKey("sign") as String
        level = aDecoder.decodeIntegerForKey("level")
        problems = aDecoder.decodeIntegerForKey("problems")
        time = aDecoder.decodeIntegerForKey("time")
        skipWrongAnswers = aDecoder.decodeBoolForKey("skipWrongAnswers")
    }

    override init() {
    }
}




   //********Here is the data archiving and retrieving class********
    class ArchiveButtonStates:NSObject {

        var documentDirectories:NSArray = []
        var documentDirectory:String = ""
        var path:String = ""

        func ArchiveButtons(#buttonStates: ButtonStates) {
            documentDirectories = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)
            documentDirectory = documentDirectories.objectAtIndex(0) as String
            path = documentDirectory.stringByAppendingPathComponent("buttonStates.archive")

            if NSKeyedArchiver.archiveRootObject(buttonStates, toFile: path) {
                //println("Success writing to file!")
            } else {
                println("Unable to write to file!")
            }
        }

        func RetrieveButtons() -> NSObject {
            var dataToRetrieve = ButtonStates()
            documentDirectories = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)
            documentDirectory = documentDirectories.objectAtIndex(0) as String
            path = documentDirectory.stringByAppendingPathComponent("buttonStates.archive")
            if let dataToRetrieve2 = NSKeyedUnarchiver.unarchiveObjectWithFile(path) as? ButtonStates {
                dataToRetrieve = dataToRetrieve2 as ButtonStates
            }
            return(dataToRetrieve)
        }
    }


the following is in my ViewController where the game is played.  Only showing the relevant code for retrieving and storing objects

class mathGame: UIViewController {

var buttonStates = ButtonStates()

override func viewWillAppear(animated: Bool) {
        super.viewWillAppear(animated)
        //set inital view

        //retrieving a stored object & placing property into local class variables
        buttonStates = ArchiveButtonStates().RetrieveButtons() as ButtonStates
        gameData.sign = buttonStates.sign
        gameData.level = buttonStates.level
        gameData.problems = buttonStates.problems
        gameData.time = buttonStates.time

    }

override func viewWillDisappear(animated: Bool) {
        super.viewWillDisappear(animated)

      //storing the object
      ArchiveButtonStates().ArchiveButtons(buttonStates: buttonStates)
    }
}

Answer 3

You need your class to adopt the NSCoding protocol and encode and decode itself, like this:

https://github.com/mattneub/Programming-iOS-Book-Examples/blob/master/bk2ch23p798basicFileOperations/ch36p1053basicFileOperations/Person.swift

Now you can transform an instance of your class into an NSData by calling NSKeyedArchiver.archivedDataWithRootObject: - and an NSData can go into NSUserDefaults.

This also means that an NSArray of instances of your class can be transformed into an NSData by the same means.