upgrading class to swift 3

ImageLoader.swift

@@ -11,7 +11,7 @@ import Foundation
 
 class ImageLoader {
 
-    let cache = NSCache()
+    let cache = NSCache<NSString, AnyObject>()
 
     class var sharedLoader : ImageLoader {
     struct Static {
@@ -20,36 +20,39 @@ class ImageLoader {
         return Static.instance
     }
 
-	func imageForUrl(urlString: String, completionHandler:(image: UIImage?, url: String) -> ()) {
-		dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), {()in
-			let data: NSData? = self.cache.objectForKey(urlString) as? NSData
+	func imageForUrl(urlString: String, completionHandler: @escaping (_ image: UIImage?, _ url: String) -> ()) {
+
+		DispatchQueue.global(qos: .background).async {
+
+			let data: NSData? = self.cache.object(forKey: urlString as NSString) as? NSData
 
 			if let goodData = data {
-				let image = UIImage(data: goodData)
-				dispatch_async(dispatch_get_main_queue(), {() in
-					completionHandler(image: image, url: urlString)
-				})
+				let image = UIImage(data: goodData as Data)
+				DispatchQueue.main.async {
+					completionHandler(image, urlString)
+				}
 				return
 			}
 
-			let downloadTask: NSURLSessionDataTask = NSURLSession.sharedSession().dataTaskWithURL(NSURL(string: urlString)!, completionHandler: {(data: NSData?, response: NSURLResponse?, error: NSError?) -> Void in
+			let session = URLSession.shared
+			let request = URLRequest(url: URL(string: urlString)!);
+
+			session.dataTask(with: request) { data, response, error in
+
 				if (error != nil) {
-					completionHandler(image: nil, url: urlString)
+					completionHandler(nil, urlString)
 					return
 				}
 
-				if let data = data {
+				if let data = data{
 					let image = UIImage(data: data)
-					self.cache.setObject(data, forKey: urlString)
-					dispatch_async(dispatch_get_main_queue(), {() in
-						completionHandler(image: image, url: urlString)
-					})
-					return
+					self.cache.setObject(data as AnyObject, forKey: urlString as NSString)
+					DispatchQueue.main.async {
+						completionHandler(image, urlString)
+					}
 				}
-
-			})
-			downloadTask.resume()
-		})
-
+			}.resume()
+
+		}
 	}
-}
+}