从JSON加载数据的方式较短

Question

我是编码新手。我发现加载JSON的代码和代码都有效，但是编写这段代码的方法较短。我认为有，但我需要一些帮助。感谢

import UIKit

class TableController: UITableViewController {
    var TableData:Array< String > = Array < String >()
    override func viewDidLoad() {
        super.viewDidLoad()
        get_data_from_url("http://www.kaleidosblog.com/tutorial/tutorial.json")
    }

    override func numberOfSectionsInTableView(tableView: UITableView) -> Int {
        return 1
    }

    override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return TableData.count
    }

    override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCellWithIdentifier("cell", forIndexPath: indexPath) 
        cell.textLabel?.text = TableData[indexPath.row]
        return cell
    }

    func get_data_from_url(url:String)
    {
      //  let httpMethod = "GET"
      //  let timeout = 15
        let url = NSURL(string: url)
        let urlRequest = NSMutableURLRequest(URL: url!,
            cachePolicy: .ReloadIgnoringLocalAndRemoteCacheData,
            timeoutInterval: 15.0)
        let queue = NSOperationQueue()
        NSURLConnection.sendAsynchronousRequest(
            urlRequest,
            queue: queue,
            completionHandler: {(response: NSURLResponse?,
                data: NSData?,
                error: NSError?) in
                if data!.length > 0 && error == nil{
                    let json = NSString(data: data!, encoding: NSASCIIStringEncoding)
                    self.extract_json(json!)
                }else if data!.length == 0 && error == nil{
                    print("Nothing was downloaded")
                } else if error != nil{
                    print("Error happened = \(error)")
                }
            }
        )
    }

    func extract_json(data:NSString)
    {
        var parseError: NSError?
        let jsonData:NSData = data.dataUsingEncoding(NSASCIIStringEncoding)!
        let json: AnyObject?
        do {
            json = try NSJSONSerialization.JSONObjectWithData(jsonData, options: [])
        } catch let error as NSError {
            parseError = error
            json = nil
        }
        if (parseError == nil)
        {
            if let countries_list = json as? NSArray
            {
                for (var i = 0; i < countries_list.count ; i++ )
                {
                    if let country_obj = countries_list[i] as? NSDictionary
                    {
                        if let country_name = country_obj["country"] as? String
                        {
                            if let country_code = country_obj["code"] as? String
                            {
                                TableData.append(country_name + " [" + country_code + "]")
                            }
                        }
                    }
                }
            }
        }
        do_table_refresh();
    }

    func do_table_refresh()
    {
        dispatch_async(dispatch_get_main_queue(), {
            self.tableView.reloadData()
            return
        })
    }
}