ISSPlayground.swift

//: Playground - Track the ISS from a playground

import MapKit
import XCPlayground

class ISSFetcher: NSObject {
    var completion: (Double, Double) -> Void
    var timer: NSTimer?
    
    init(inCompletion: (Double, Double) -> Void) {
       completion = inCompletion
    }
    
    func getNext() {
        guard let url = NSURL(string: "http://api.open-notify.org/iss-now.json") else {
            print("we need a url")
            return
        }
        let request = NSURLRequest(URL: url)
        let session = NSURLSession.sharedSession()
        let task = session.dataTaskWithRequest(request, completionHandler: { (data, response, error) in
            if let data = data, json = try? NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions()) as? [String: AnyObject],
                position = json?["iss_position"],
                latitude = position["latitude"],
                longitude = position["longitude"] {
                self.completion(latitude as! Double, longitude as! Double)
            }
            if let error = error {
                print("error fetching new coordinates", error)
            }
        })
        task.resume()
    }
    
    func stop() {
        timer?.invalidate()
    }
    
    func start() {
        // kick things off
        getNext()
        
        // set it up so we do it again after 5 seconds
        timer = NSTimer.scheduledTimerWithTimeInterval(5.0, target: self, selector: #selector(getNext), userInfo: nil, repeats: true)
    }
}


class ISSAnnotation: NSObject, MKAnnotation {
    
    dynamic var coordinate: CLLocationCoordinate2D
    var title: String? = "ISS"
    
    init(lat: Double, lon: Double) {
        coordinate = CLLocationCoordinate2D(latitude: lat, longitude: lon)
    }
    
    func update(newLatitude: Double, newLongitude: Double) {
        coordinate = CLLocationCoordinate2D(latitude: newLatitude, longitude: newLongitude)
    }
    
}

// This is our main()

let frame = CGRect(x: 0, y: 0, width: 400, height: 400 )
let mapView = MKMapView(frame: frame )
mapView.mapType = .Satellite
let annotation = ISSAnnotation(lat: 0,lon: 0)
mapView.addAnnotation(annotation)

// Create the fetcher object with completion block
let fetcher = ISSFetcher(inCompletion: {(lat, lon) in
    dispatch_async(dispatch_get_main_queue(), {
        UIView.animateWithDuration(3, animations: {
            print("new coordinates", lat, lon)
            annotation.update(lat, newLongitude: lon)
            mapView.centerCoordinate = annotation.coordinate
        })
    })
})

// start the fetcher
fetcher.start()

// view the map in the timeline!
XCPlaygroundPage.currentPage.liveView = mapView

This one is purely preference, but I like the look of this trailing closure syntax better (I think this is what pzearfoss was referring to, though there are many variations of syntax closure syntax). There are many many people who will say they like other ways better, because there are lots of ways of writing closure syntax, but the trailing ')' at the end of a method is just less appealing to me. The argument that most people have is that your current syntax looks more like a closure, so its' more obvious what is going on, I just think this way is cleaner, and I've gotten used to it. There is no performance benefit, strictly which syntax works better for whatever team/person is working on the code:

// Create the fetcher object with completion block
let fetcher = ISSFetcher() { lat, lon in
    dispatch_async(dispatch_get_main_queue()) {
        UIView.animateWithDuration(3) {
            print("new coordinates", lat, lon)
            annotation.update(lat, newLongitude: lon)
            mapView.centerCoordinate = annotation.coordinate
        }
    }
}




let task = session.dataTaskWithRequest(request) { data, response, error in
            if let data = data, json = try? NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions()) as? [String: AnyObject],
                position = json?["iss_position"],
                latitude = position["latitude"],
                longitude = position["longitude"] {
                self.completion(latitude as! Double, longitude as! Double)
            }
            if let error = error {
                print("error fetching new coordinates", error)
            }
  }