Basic Async UIImageView

UIImageView+AsyncExtension.swift

import Foundation
import UIKit

extension UIImageView {
    func setImageWithUrlString(urlString : String, placeholderImageFileName : String?){
        if let placeholderImageFileName = placeholderImageFileName {
            self.setImageOnMainThread(UIImage(named: placeholderImageFileName))
        }
        let url = NSURL(string: urlString)!
        let request = NSMutableURLRequest(URL: url, cachePolicy: .ReturnCacheDataElseLoad, timeoutInterval: 30.0)
        let task = NSURLSession.sharedSession().dataTaskWithRequest(request) { (data, response, error : NSError?) -> Void in
            guard let data = data where error == nil else {
                print("Error getting image from url \n \(error!)")
                return
            }
            let loadedImage = UIImage(data: data)
            self.setImageOnMainThread(loadedImage)
        }
        task.resume()
    }
    
    func setImageOnMainThread(imageToSet : UIImage?) {
        if NSThread.isMainThread() {
            self.image = imageToSet
        } else {
            dispatch_async(dispatch_get_main_queue(), { () -> Void in
                self.image = imageToSet
            })
        }
    }
}