swift 异步加载图片

import UIKit

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

    func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
        self.window = UIWindow(frame: UIScreen.mainScreen().bounds)
        // Override point for customization after application launch.
        self.window!.backgroundColor = UIColor.whiteColor()

        self.window!.rootViewController = RootViewController();

        self.window!.makeKeyAndVisible()
        return true
    }
}

import UIKit

class RootViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        let imageView = UIImageView.init(frame: UIScreen.mainScreen().bounds);
        imageView.backgroundColor = UIColor.greenColor()
        self.view.addSubview(imageView)

        let url:NSURL = NSURL.init(string: "http://pic2.ooopic.com/11/86/60/84bOOOPIC13.jpg")!
        let request:NSURLRequest = NSURLRequest(URL: url)
        //异步加载图片
        NSURLConnection.sendAsynchronousRequest(request, queue: NSOperationQueue.mainQueue(), completionHandler:{ (response, data, error) -> Void in
             let image = UIImage(data: data!)
            imageView.image = image

     })
    }
}