KeyValueApp

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Hi, I'm Kristen––an iOS development newbie and [Nice Mohawk](http://nicemohawk.com)’s summer intern. Most recently, I was assigned the task of building a simple example app that uses iCloud to store key-value data.

As one would expect, I immediately looked for a tutorial on the subject. I was disappointed, however, to come up short: all of the tutorials I found were written in Objective-C and I––the newbie who only knows Swift––could only half understand what was going on.

Thankfully, I did eventually figure out how to do all of this in Swift. It wasn’t too bad, either.

I decided to build an app with a text field and button, so that a user can type a short message and save it to iCloud. I began by setting up [iCloud entitlements (see steps 1 & 2)](http://code.tutsplus.com/tutorials/working-with-icloud-key-value-storage--pre-37542).

I then opened my ViewController.swift file and declared and initialized an ```NSUbiquitousKeyValueStore``` object:

var iCloudKeyStore: NSUbiquitousKeyValueStore? = NSUbiquitousKeyValueStore()

The NSUbiquitousKeyValueStore class allows you to save values of various types––NSNumber, NSString, NSDictionary, etc.––and associate them with a key. To save the user’s message for my app, I created an outlet for my text field and a function to call the ```setString:forKey``` and ```synchronize``` methods. ```setString:forKey:``` pairs the text field’s contents with a key, while synchronize saves the message to iCloud.

let iCloudTextKey = “iCloudText”
    @IBOutlet weak var textField: UITextField!  
        
    …
        
    func saveToiCloud() {
        iCloudKeyStore?.setString(textField.text, forKey: iCloudTextKey)
        iCloudKeyStore?.synchronize()
    }

I later realized that I should display the last message the user saved upon launching the app. To do this, I made a function that uses optional chaining and the ```stringForKey:``` method to check for and display a previously saved message.

func iCloudSetUp() {
        if let savedString = iCloudKeyStore?.stringForKey(iCloudTextKey) {
            textField.text = savedString
        }
    }

Within the same function, I also registered for the ```NSUbiquitousKeyValueStoreDidChangeExternallyNotification``` notification so that my app could handle any changes made to the text field by other instances of the app while running. Using the ```addObserver``` method to do this also requires an additional function to take some sort of action. In my case, I made this function update the message in the text field.

func iCloudSetUp() {
        …
        NSNotificationCenter.defaultCenter().addObserver(self, 
        	selector: “ubiquitousKeyValueStoreDidChangeExternally:", 
        	name:  NSUbiquitousKeyValueStoreDidChangeExternallyNotification, 
        	object: iCloudKeyStore)
    }
      
    func ubiquitousKeyValueStoreDidChangeExternally() {
        textField.text = iCloudKeyStore?.stringForKey(iCloudTextKey)
    }

The finished project is slightly more complicated, as I decided to incorporate a switch that allows the user to save text locally using ```NSUserDefaults``` or to iCloud.

And that's it! Not too bad, right?

KeyValueApp

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