问如何设置Swift变量以使它们具有适当的范围

EN

@IBAction func LoginBtn(_ sender: Any) {

    //created NSURL
    let requestURL = NSURL(string: URL_SERVICE)

    //creating NSMutableURLRequest
    let request = NSMutableURLRequest(url: requestURL! as URL)

    //setting the method to post
    request.httpMethod = "POST"

    //getting values from text fields
    let mode = "login"
    let userid = EmployeeID.text

    var postResponse : String?
    var postMessage : String?


    //creating the post parameter by concatenating the keys and values from text field
    let postParameters = "mode="+mode+"&userid="+userid!;


    //adding the parameters to request body
    request.httpBody = postParameters.data(using: String.Encoding.utf8, allowLossyConversion: false)

    //creating a task to send the post request
    let task = URLSession.shared.dataTask(with: request as URLRequest){
        data, response, error in

        if error != nil{
            print("error is \(String(describing: error))")
            return;
        }

        //parsing the response
        do {
            //converting resonse to NSDictionary
            let myJSON =  try JSONSerialization.jsonObject(with: data!, options: .mutableContainers) as? NSDictionary
            //parsing the json
            if let parseJSON = myJSON {
                //getting the json response
                postResponse = (parseJSON["AppID"] as! String)
                postMessage = (parseJSON["message"] as! String)
                //username = parseJSON["username"] as! String?
                print(postMessage!)
                print(postResponse!)

            }
        } catch {
            print(error)
        }
    }

    task.resume()

    print("userid \(String(describing: userid)) resp \(String(describing: postResponse))")

    if userid != postResponse { 
        EmployeeID.text = ""
        let alertController = UIAlertController(title: "Unrecognized EmployeeID \(login ?? "nada")", message: "Please re-type EmployeeID", preferredStyle: .alert)
        let defaultAction = UIAlertAction(title: "OK", style: .cancel, handler: nil)
        alertController.addAction(defaultAction)
        self.present(alertController, animated: true, completion: nil)
    }else{

    }

}