My app Data does not refresh but does make network calls?

import UIKit

class ViewController: UIViewController {

    //Replace the string below with your API Key.
    private let apiKey = "c35888949fe1669241327912c904199f"

    @IBOutlet weak var iconView: UIImageView!
    @IBOutlet weak var currentTimeLabel: UILabel!
    @IBOutlet weak var temperatureLabel: UILabel!
    @IBOutlet weak var humidityLabel: UILabel!
    @IBOutlet weak var precipitationLabel: UILabel!
    @IBOutlet weak var summaryLabel: UILabel!
    @IBOutlet weak var sunsetLabel: UILabel!
    @IBOutlet weak var sunriseLabel: UILabel!




    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        let baseURL = NSURL(string: "https://api.forecast.io/forecast/\(apiKey)/")
        let forecastURL = NSURL(string: "51.515611, -0.133184", relativeToURL: baseURL)


        let sharedSession = NSURLSession.sharedSession()
        let downloadTask: NSURLSessionDownloadTask = sharedSession.downloadTaskWithURL(forecastURL, completionHandler: { (location: NSURL!, response: NSURLResponse!, error: NSError!) -> Void in
            println(response)

            if (error == nil) {
                let dataObject = NSData(contentsOfURL: location)
                let weatherDictionary: NSDictionary = NSJSONSerialization.JSONObjectWithData(dataObject, options: nil, error: nil) as NSDictionary

                let currentWeather = Current(weatherDictionary: weatherDictionary)

                dispatch_async(dispatch_get_main_queue(), { () -> Void in
                    self.temperatureLabel.text = "\(currentWeather.temperature)"
                    self.iconView.image = currentWeather.icon!
                    self.currentTimeLabel.text = "At \(currentWeather.currentTime!) it is"
                    self.humidityLabel.text = "\(currentWeather.humidity)"
                    self.precipitationLabel.text = "\(currentWeather.precipProbability)"
                    self.summaryLabel.text = "\(currentWeather.summary)"
                    self.sunriseLabel.text = "\(currentWeather).sunriseTime"
                    self.sunsetLabel.text = "\(currentWeather).sunsetTime"

                })

            }

        })

        downloadTask.resume()
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }


}

import Foundation
import UIKit

struct Current {

    var currentTime: String?
    var sunriseTime: Int
    var sunsetTime: Int
    var temperature: Int
    var humidity: Double
    var precipProbability: Double
    var summary: String
    var icon: UIImage?

    init(weatherDictionary: NSDictionary) {
        let currentWeather = weatherDictionary["currently"] as NSDictionary

        temperature = currentWeather["temperature"] as Int
        humidity = currentWeather["humidity"] as Double
        precipProbability = currentWeather["precipProbability"] as Double
        summary = currentWeather["summary"] as String
        sunriseTime = currentWeather["sunriseTime"] as Int
        sunsetTime = currentWeather["sunsetTime"] as Int

        let currentTimeIntVale = currentWeather["time"] as Int
        currentTime = dateStringFromUnixTime(currentTimeIntVale)

        let iconString = currentWeather["icon"] as String
        icon = weatherIconFromString(iconString)
    }

    func dateStringFromUnixTime(unixTime: Int) -> String {
        let timeInSeconds = NSTimeInterval(unixTime)
        let weatherDate = NSDate(timeIntervalSince1970: timeInSeconds)

        let dateFormatter = NSDateFormatter()
        dateFormatter.timeStyle = .ShortStyle

        return dateFormatter.stringFromDate(weatherDate)
    }

    func weatherIconFromString(stringIcon: String) -> UIImage {
        var imageName: String

        switch stringIcon {
        case "clear-day":
            imageName = "Sun-thin"
        case "clear-night":
            imageName = "Moon-thin"
        case "rain":
            imageName = "Rain-thin"
        case "snow":
            imageName = "Snow-thin"
        case "sleet":
            imageName = "Hail-thin"
        case "wind":
            imageName = "windy-thin"
        case "fog":
            imageName = "Haze-thin"
        case "cloudy":
            imageName = "cloudy"
        case "partly-cloudy-day":
            imageName = "PartlySunny-thin"
        case "partly-cloudy-night":
            imageName = "PartlyMoon-thin"
        default:
            imageName = "AppIcon"
        }

        var iconName = UIImage(named: imageName)
        return iconName
    }

}