Delegation and NSNotificationCenter

Delegate Design Pattern

1. Create a delegate protocol that defines the responsibilities of the delegate.
2. Create a delegate property in the delegating class to keep track of the delegate.
3. Adopt and implement the delegate methods in the delegate class.
4. Call the delegate from the delegating object.

Example:

// Our Delegate
protocol DudeUpdater {
    func dudeDidUpdateAge(sender: Dude)
}

public class Dude: NSObject {

    // Dude Delegate
    var delegate: DudeUpdater?

    dynamic var age = 1
    private var timer: NSTimer?

    override init() {
        super.init()
        self.timer = NSTimer.scheduledTimerWithTimeInterval(5.0, target: self,
                                                            selector: #selector(getOlder), userInfo: nil, repeats: true)
    }

    public func getOlder() {
        self.age += 1
        print(self.age)

        // Dude Delegate is called here
        delegate?.dudeDidUpdateAge(self)
    }
}

// UIView
// This conforms to the delegate
public class DudeDisplayer: UIView, DudeUpdater {

    private var dude: Dude!
    private var label: UILabel!
    private var myContext = 0


    convenience init(dude: Dude, frame: CGRect) {
        self.init(frame: frame)

        // Initializes The Dude
        self.dude = dude

        // Sets the delegate of the dude
        dude.delegate = self
        self.label = UILabel(frame: CGRect(x: 50, y: 50, width: 60, height: 50))
        self.label.backgroundColor = UIColor.redColor()
        self.label.textAlignment = .Center
        label.textColor = .whiteColor()
        self.addSubview(self.label)

        self.backgroundColor = .whiteColor()

    }

    // Delegate Method
    // this is the delegate method, that updates the label with the Dude's age.
    func dudeDidUpdateAge(sender: Dude){
        label.text = "Age: \(String(sender.age))"
    }

}

NSNotification Pattern

The basic configuration to set up a proper notification requires two parts: • a sender class that posts the notification • and a receiver class that observes the post.

Sender Class

A sender class can be any class that you want to actually post or send the notification, we do this by using NSNotificationCenter's postNotificationName.

Receiver Class

A receiver class can be any class that you want that will receive or observe notifications, we do this by using NSNotificationCenter's addObserver or addObserverName methods.

Example:

/// NSNotificationCenter

// We use this as our notification center key
let dudeNotificationKey = "dude.did.update"
public class Dude: NSObject {


    dynamic var age = 1
    private var timer: NSTimer?

    // The Dude's NotificationCenter
    let notificationCenter = NSNotificationCenter.defaultCenter()

    override init() {
        super.init()
        self.timer = NSTimer.scheduledTimerWithTimeInterval(5.0, target: self,
                                                            selector: #selector(getOlder), userInfo: nil, repeats: true)
    }

    public func getOlder() {
        self.age += 1
        print(self.age)
        // The Dude's Notification Center posts the Dude's age - the age is contained in the dictionary.
        notificationCenter.postNotificationName(dudeNotificationKey, object: nil, userInfo: ["age": self.age])
    }

}

// UIView
public class DudeDisplayer: UIView {

    private var dude: Dude!
    private var label: UILabel!
    private var myContext = 0

    // The DudeDisplayer's Notification Center
    let notificationCenter = NSNotificationCenter.defaultCenter()

    convenience init(dude: Dude, frame: CGRect) {
        self.init(frame: frame)

        // Initializes The Dude
        self.dude = dude

        // The DudeDisplayer's NotificationCenter is listening for the update, and will
        // call updateLabelWithNotification when it "hears it"
        notificationCenter.addObserver(self, selector: #selector(updateLabelWithNotification), name: dudeNotificationKey, object: nil)

        self.label = UILabel(frame: CGRect(x: 50, y: 50, width: 80, height: 50))
        self.label.backgroundColor = UIColor.redColor()
        self.label.textAlignment = .Center
        label.textColor = .whiteColor()
        self.addSubview(self.label)

        self.backgroundColor = .whiteColor()

    }

    // This method is called when the DudeDisplayer's NotificationCenter receives a NSNotification.
    // The method takes a notification, and parses out the Dude's age from the userInfo dictionary.
    // The text of the label is then updated.
    func updateLabelWithNotification(notification: NSNotification) {
        let userInfo = notification.userInfo as! [String: Int]
        label.text = "Age: \(userInfo["age"]!)"
    }  
}