How to encode an array of CGPoints with NSCoder in Swift?

Question

I am trying to save a copy of my custom class to a file, my class has 2 arrays of CGPoints which I append to every so often, they look like this:

class BlockAttributes: NSObject {
    var positions:[CGPoint] = []
    var spawns:[CGPoint] = []
}

Everything is working great as far as just as using and accessing the class goes, but archiving it does not work. I can archive arrays of Strings, Bools, and Ints just fine in my other classes but my game fails every time I try to use NSCoder to encode my arrays of CGPoints. Here is my code for archiving:

func encodeWithCoder(coder: NSCoder!) {
    coder.encodeObject(positions, forKey: "positions")
    coder.encodeObject(spawns, forKey: "spawns")
}

....

class ArchiveData: NSObject {

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

    func saveData(data: BlockAttributes) {
        documentDirectories = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)
        documentDirectory = documentDirectories.objectAtIndex(0) as! String
        path = documentDirectory.stringByAppendingPathComponent("data.archive")

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

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

.... And to save:

let archiveData = ArchiveData()
archiveData.saveData(myBlockActionsObject)

I even tried creating my own custom class to save the CGPoints to, which I call MyCGPoint (I read somewhere on SO that creating custom classes for some data types resolves some NSCoder issues):

class MyCGPoint: NSObject {
    var x: CGFloat = 0.0
    var y: CGFloat = 0.0

    init(X: CGFloat, Y: CGFloat) {
        x = X
        y = Y
    }

    override init() {

    }
}

....

class BlockAttributes: NSObject {
    var positions:[MyCGPoint] = []
    var spawns:[MyCGPoint] = []
}

But alas, I am still getting this error:

[Game.MyCGPoint encodeWithCoder:]:
unrecognized selector sent to instance 0x137f1d1a0 Game[20953:5814436]
*** Terminating app due to uncaught exception 'NSInvalidArgumentException',
reason: '-[Game.MyCGPoint encodeWithCoder:]:
unrecognized selector sent to instance 0x137f1d1a0'

Any idea how I can use encodeObject to encode my array of CGPoints/MyCGPoints?

Answer 1

CGPoint (and its Cocoa's twin NSPoint ) are structs, ie value type, so you can't encode them directly. Wrap them in NSValue :

let positionValues = positions.map { NSValue(point:$0) }
let spawnValues    = spawns.map    { NSValue(point:$0) }

coder.encodeObject(positionValues, forKey: "positions")
coder.encodeObject(spawnValues, forKey: "spawns")

// Decode:
positons = (coder.decodeObjectForKey("positions") as! [NSValue]).map { $0.pointValue }
spawns   = (coder.decodeObjectForKey("spawns")    as! [NSValue]).map { $0.pointValue }

When you write your custom wrapper class, you have to make it compliant with NSCoding too, which NSValeu had already done for you, for free.

Answer 2

You can convert them to and from strings:

//To string
let point = CGPointMake(0, 0)
let string = NSStringFromCGPoint(point)
//Or if you want String instead of NSString
let string = String(point)

//From string
let point2 = CGPointFromString(string)