Swift: Updating a label from a second view controller - swift

Question

I have two view controllers. I also have a universal variable called number. The first view controller has a label on it called mainLabel. My second view controller has a button on it. When the button is pressed it should subtract 200 from the variable number then update the mainLabel label. I can not figure out how to make mainLabel a label that works on the second view controller too.
First View Controller
import UIKit
var number:Int = 0
class ViewController: UIViewController {
#IBOutlet weak var mainLabel: UILabel!
#IBAction func backgroundButton(sender: AnyObject) {
number = number + 1
mainLabel.text = "\(number)"
NSUserDefaults.standardUserDefaults().setObject(number, forKey: "number")
}
override func viewDidLoad() {
super.viewDidLoad()
if NSUserDefaults.standardUserDefaults().objectForKey("number") != nil {
number = NSUserDefaults.standardUserDefaults().objectForKey("number") as! Int
}
mainLabel.text = "\(number)"
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
}
Second View Controller
import UIKit
class SecondViewController: UIViewController {
#IBOutlet weak var buy1Label: UILabel!
#IBAction func buy1(sender: AnyObject) {
number = number - 200
buy1Label.text = "Bought!"
mainLabel.text = "\(number)"
}
}

Answer 1

class ViewController: UIViewController {
#IBOutlet weak var mainLabel: UILabel!
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
NSNotificationCenter.defaultCenter().addObserverForName("NSNotificationName", object: nil, queue: nil) { (note) -> Void in
// Number changed, update your UILabel.
var number: Int = NSUserDefaults.standardUserDefaults().integerForKey("keyOfNumber")
self.mainLabel.text = "\(number)"
}
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
#IBAction func subtractNumberBy200() {
var number: Int = NSUserDefaults.standardUserDefaults().integerForKey("keyOfNumber")
number -= 200
NSUserDefaults.standardUserDefaults().setInteger(number, forKey: "keyOfNumber")
}
}
Hope this will works for you.

Answer 2

Wow, this question cuts to the core of what I have to deal with every day. Here is my first take on how to do this with notifications.
First, setup some common global things.
let NumberDidChangeNote = "NumberDidChangeNote" // A name for the notification.
// A function to get the value of number the same way every time.
func number() -> Int {
return NSUserDefaults.standardUserDefaults().integerForKey("number");
}
// A function to set the value of number the same way every time.
func setNumber(number: Int) {
NSUserDefaults.standardUserDefaults().setInteger(number, forKey: "number")
NSUserDefaults.standardUserDefaults().synchronize()
// Post a number did change notification
NSNotificationCenter.defaultCenter().postNotificationName(NumberDidChangeNote, object: nil)
}
The first view controller splits the roles of setting number and setting the label.
class ViewController: UIViewController {
#IBOutlet weak var mainLabel: UILabel!
#IBAction func backgroundButton(sender: AnyObject) {
setNumber(number() + 1)
}
dynamic func numberDidChange(note: NSNotification) {
mainLabel.text = "\(number())"
}
override func viewWillAppear(animated: Bool) {
super.viewWillAppear(animated)
// Add an observer which will call numberDidChange() anytime the number changes.
let center = NSNotificationCenter.defaultCenter()
center.addObserver(self, selector: "numberDidChange", name: NumberDidChangeNote, object: nil)
// Fake an initial notification to numberDidChange() to set the initial value of the label.
numberDidChange(NSNotification(name: NumberDidChangeNote, object: nil))
}
override func viewWillDisappear(animated: Bool) {
// Remove the observer when not on the screen.
let center = NSNotificationCenter.defaultCenter()
center.removeObserver(self, name: NumberDidChangeNote, object: nil)
super.viewWillDisappear(animated)
}
}
Now the second view controller doesn't have to worry about the first view controller at all.
class SecondViewController: UIViewController {
#IBOutlet weak var buy1Label: UILabel!
#IBAction func buy1(sender: AnyObject) {
setNumber(number() - 200)
buy1Label.text = "Bought!"
}
}