Coding array with NSCoder Swift

Question

I'm trying to implement the NSCoder, but am currently facing a stubborn issue. My goal is to save the array of strings via NSCoder to a local file and load it when the app opens next time.

Here is the class i've created, but i'm not sure how i should handle the init and encoder functions:

class MyObject: NSObject, NSCoding {

var storyPoints: [String] = []

init(storyPoints : [String]) {
    self.storePoints = storePoints
}


required init(coder decoder: NSCoder) {
    super.init()

???

}

func encodeWithCoder(coder: NSCoder) {
???
}

}

Moreover, how do i access it in my view controller? where should i declare a path for saving the NSCoder? It's not really clear enough.

Looking forward to any advices.

Thank you.

take a look at the link raywenderlich.com/12779/… to get clear picture about persisiting user data with the help of NSCoder and NSKeyedArcheiver — vignesh kumar
– vignesh kumar, Commented Sep 11, 2015 at 15:01

Price Ringo · Accepted Answer · 2015-09-11 15:23:13Z

2

Here is an implementation and a playground example that saves the object to the /tmp directory. The init(coder:) function overrides NSObject's so is required and since it is not a designated initializer it must be marked as convenience. Also because init(coder:) is a convenience initializer, it can not call super.init().

To directly answer your question about archiving an array, just type cast the result from decoderObjectForKey(_:). Check the NSCoding documentation for information and API's to code/decode. There is a lot there.

import Cocoa

class MyObject: NSObject, NSCoding {

  var storyPoints: [String] = []

  init(storyPoints : [String]) {
    self.storyPoints = storyPoints
  }

  convenience required init(coder decoder: NSCoder) {
    let storyPoints = decoder.decodeObjectForKey("storypoints") as! [String]
    self.init(storyPoints: storyPoints)
  }

  func encodeWithCoder(coder: NSCoder) {
    coder.encodeObject(storyPoints, forKey: "storypoints")
  }
}

edited Sep 11, 2015 at 15:23

answered Sep 11, 2015 at 15:09

Price Ringo

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5 Comments

David Robertson Over a year ago

Thank you! Works nicely, but each time i run the app the array values are reassigned as if no changes happened.

Price Ringo Over a year ago

Can you confirm that you are calling the archiveRootObject(_:toFile:) method after the changes are made to your object?

David Robertson Over a year ago

yes i'm doing it in the function code - right after the obj.storyPoints.append(newObject) happens. yet when i restart - the array is blank again.

David Robertson Over a year ago

there is a little difficulty, because - i can append the array either with one function or the other separately. so to access MyObject array from both functions i declared it on the top before viewDidLoad. What i don't understand is - i have to declare the NSKeyedArchiver and the rest of the code twice in two separate functions?

Price Ringo Over a year ago

Be sure that you are using MVC best practices. Do use NSCoding for initializing and saving your model. How your view controllers access the model is important but can't be handled here in comments. Don't worry about the cost of instantiating NSKeyedArchiver/Unarchiver. It is a singleton and should be used as needed.

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