swift4でyoutube api

import UIKit
import Alamofire

class Model: NSObject {
    private var youtubeNextPageToken: String?
    
    func loadYoutubeList(callback: (youtubeList: YoutubeList) -> (), fail:((error: NSError) ->())){
        
        let req = request(.GET, AppConfig.youtubeURL())
        req.response { (request, response, responseData, error) -> Void in
            do {
                let jsonResult = try NSJSONSerialization.JSONObjectWthData(responseData!, options: NSJSONReadingOptions.MutableContainers) as! NSMutableDictionary
                
                self.youtubeNextPageToken = jsonResult["nextPageToken"] as! String?
                let ary = jsonResult["items"] as! NSArray
                let youtubeList = YoutubeList(ary: ary)
                callback(youtubeList: youtubeList)
            } catch {
                print("loadYoutubeList error")
            }
        }
    }
}

constrainをつけて行きます。