NetworkExtensions.swift

extension NSURLSession{
    
    // This extension provides an API that hides any explicit use of GCD
    // functions.
    
    // Just make sure you use the correct closure to update your UI(completionHandler:) and
    // everything should work fine.
    
    // If you wish to understand this code and know more about GCD and how to
    // run closures in the background, make sure to check the GCD course
    
    
    /*
    * 
    * downloadHandler: runs in the delegate queue (background)
    * completionHandler: runs in the MAIN QUEUE. Use it to update your UI
    */
    public func dataTaskWithRequest(request: NSURLRequest,
        downloadHandler: (data: NSData? , response: NSURLResponse?, error: NSError?) -> Void,
        completionHandler:()->Void) -> NSURLSessionDataTask{
            
            return dataTaskWithRequest(request) { (data, response, error) -> Void in
                
                // delegate queue
                downloadHandler(data: data, response: response, error: error)
                
                // Move to the MainQueue and run the completion block
                dispatch_async(dispatch_get_main_queue(), { () -> Void in
                    completionHandler()
                })
            }
    }
}