Persistant storage for array of objects in Swift

Question

I need help in creating methods for reading/writing some objects to a file, for persistent storage. I've been stuck on this for the last 3 days. This is where I got:

My object:

class Item: NSObject {
var name : String = ""
var link : String = ""
var state : String = ""
var type : String = ""
var selected = false

func createItemWith(name:String, link:String, state:String, type:String) {
    self.name = name
    self.link = link
    self.state = state
    self.type = type
}
}

Then I add it to an array

self.itemsArray.addObject(item)

Now, each object represents a cell in a collection view, where the user can interact with it

   func collectionView(collectionView: UICollectionView,
    didSelectItemAtIndexPath indexPath: NSIndexPath) {
        let cell = self.collectionView.cellForItemAtIndexPath(indexPath)
        var cellCheckedImage = cell!.contentView.viewWithTag(20) as! UIImageView
        if ((itemsArray.objectAtIndex(indexPath.row) as! Item).selected == false) {
            cellCheckedImage.image = UIImage(named:"Checked")
            self.selectedItemsArray.append(itemsArray.objectAtIndex(indexPath.row) as! Item)
            (itemsArray.objectAtIndex(indexPath.row) as! Item).selected = true
        } else if ((itemsArray.objectAtIndex(indexPath.row) as! Item).selected == true) {
            cellCheckedImage.image = UIImage(named:"Unchecked")
            (itemsArray.objectAtIndex(indexPath.row) as! Item).selected = false
        }
}

Now, you can see, the items which the user interacted with I will move to a second array

self.selectedItemsArray.append(itemsArray.objectAtIndex(indexPath.row) as! Item)

which is

   var selectedItemsArray = [Item]()

Now, I have a second class which should write the previous array to a file

import Foundation

private let _SelectedItemsSharedInstance = SelectedItems()

class SelectedItems: NSObject {

private var itemsKey = "items"
var selectedItems = Array("")

class var sharedInstance: SelectedItems {
    return _SelectedItemsSharedInstance
}

func loadItemsFromFile() {
    // getting path 
    let paths = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true) as NSArray
    let documentsDirectory = paths[0] as! String
    let path = documentsDirectory.stringByAppendingPathComponent("SelectedItems.plist")
    let fileManager = NSFileManager.defaultManager()
    //check if file exists
    if(fileManager.fileExistsAtPath(path)) {


    }
}

func writeItemsToFile() {
    let paths = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true) as NSArray
    let documentsDirectory = paths.objectAtIndex(0) as! NSString
    let path = documentsDirectory.stringByAppendingPathComponent("SelectedItems.plist")
}
}

This is where I'm stuck. How can I write and read selectedItems to a file?

Update: this is how it worked My Object:

class Item: NSObject {
var name : NSString = ""
var link : NSString = ""
var state : NSString = ""
var type : NSString = ""
var selected = false

func createItemWith(name:String, link:String, state:String, type:String) {
    self.name = name
    self.link = link
    self.state = state
    self.type = type
}

init(name: NSString, link: NSString, state: NSString, type: NSString)
{
    self.name = name
    self.link = link
    self.state = state
    self.type =  type
}

required init(coder aDecoder: NSCoder) {
    self.link = aDecoder.decodeObjectForKey("link") as! NSString as String
    self.name = aDecoder.decodeObjectForKey("name") as! NSString as String
    self.state = aDecoder.decodeObjectForKey("state") as! NSString as String
    self.type = aDecoder.decodeObjectForKey("type") as! NSString as String
}

func encodeWithCoder(aCoder: NSCoder) {
    aCoder.encodeObject(link, forKey: "link")
    aCoder.encodeObject(name, forKey: "name")
    aCoder.encodeObject(name, forKey: "state")
    aCoder.encodeObject(name, forKey: "type")
}

}

And the methods that write and read them

func loadItemsFromFile() {
    // getting path 
    let paths = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true) as NSArray
    let documentsDirectory = paths[0] as! String
    let path = documentsDirectory.stringByAppendingPathComponent("SelectedItems.txt")
    let fileManager = NSFileManager.defaultManager()
    println(path)
    if(!fileManager.fileExistsAtPath(path)) {
        // If it doesn't, copy it from the default file in the Bundle
        if let bundlePath = NSBundle.mainBundle().pathForResource("SelectedItems", ofType: "txt") {
            let resultDictionary = NSMutableDictionary(contentsOfFile: bundlePath)
            if let data = NSKeyedUnarchiver.unarchiveObjectWithFile(path) as? [String] {
                self.selectedItemsArray = data
            }
        }
    }
    println(self.selectedItemsArray.description)
}

func writeItemsToFile() {
    let paths = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true) as NSArray
    let documentsDirectory = paths.objectAtIndex(0) as! NSString
    let path = documentsDirectory.stringByAppendingPathComponent("SelectedItems.txt")
    NSKeyedArchiver.archiveRootObject(self.selectedItemsArray, toFile: path)

}

Yes, of course, but the written file is empty. I imagine I need to encode and decode my data, when written and read. — trusk
– trusk, Commented Apr 17, 2015 at 13:19

Eric Aya · Accepted Answer · 2015-04-17 14:17:59Z

1

You can use NSKeyedArchiver and NSKeyedUnarchiver to store your array to a file. Something like this:

func applicationWillTerminate(aNotification: NSNotification) {
    NSKeyedArchiver.archiveRootObject(self.myArray, toFile: "a/file/path")
}

func applicationDidFinishLaunching(aNotification: NSNotification) {
    if let data = NSKeyedUnarchiver.unarchiveObjectWithFile("a/file/path") as? [String] {
        self.myArray = data
    }
}

In this example I use it inside the AppDelegate methods, but you can use it anywhere in your app.

answered Apr 17, 2015 at 14:17

Eric Aya

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2 Comments

trusk Over a year ago

Thank you! This did it, but it required to implement init and encodeWithCoder in my object class. I will update the parent question to reflect the changes I did!

Eric Aya Over a year ago

Oops, indeed I forgot to mention that detail.

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