Validating Information Before Moving to Next View in Swift - mysql

Question

I have an application where I need to validate some information(zip code) from a database before I allow my iOS application to proceed to the next view. I used the zip code project to import a DB Table will all valid US Zip codes, and I want to have the zip code the inputed by the user validated before I allow them to proceed. If the zip code isn't valid, I hold them up at the current view and display an alert. I have a class to validate the zip code, but the zip code isn't being validated until after the next view is loaded. I've been leaning towards using a completion handler, but I'm not exactly sure if that's my best/only option. Thanks in advance.
EDIT:
The following is the whole class for retrieve the data
protocol ZipCodeLocationProtocol: class {
func zipCodeLocationDownloaded(zipLocation: Location)
}
class RetrieveZipCodeLocation: NSObject, NSURLSessionDataDelegate {
// MARK: Properties
weak var delegate: ZipCodeLocationProtocol!
var data: NSMutableData = NSMutableData()
let urlPath: String = "xxxx"
func downloadZipCodeLocation(zipcode: Int) {
let path = self.urlPath + "?zipcode=\(zipcode)"
let url: NSURL = NSURL(string: path)!
var session: NSURLSession!
let configuration = NSURLSessionConfiguration.defaultSessionConfiguration()
session = NSURLSession(configuration: configuration, delegate: self, delegateQueue: nil)
let task = session.dataTaskWithURL(url)
task.resume()
}
func URLSession(session: NSURLSession, dataTask: NSURLSessionDataTask, didReceiveData data: NSData) {
self.data.appendData(data)
}
func URLSession(session: NSURLSession, task: NSURLSessionTask, didCompleteWithError error: NSError?) {
if error != nil {
print("Failed to download data")
}else {
print("Data downloaded")
self.parseJSON()
}
}
func parseJSON() {
var jsonResult: NSMutableArray = NSMutableArray()
var location = Location(title: "TITLE", coordinate: CLLocationCoordinate2D(latitude: 0, longitude: 0))
do {
jsonResult = try NSJSONSerialization.JSONObjectWithData(self.data, options:[]) as! NSMutableArray
} catch let error as NSError {
print(error)
}
var jsonElement: NSDictionary = NSDictionary()
for(var i = 0; i < jsonResult.count; i++) {
jsonElement = jsonResult[i] as! NSDictionary
let point = CLLocationCoordinate2D(latitude: (jsonElement["LATITUDE"] as! NSString).doubleValue, longitude: (jsonElement["LONGITUDE"] as! NSString).doubleValue)
// Get Information
location = Location(title: "TITLE", coordinate: point)
self.delegate.zipCodeLocationDownloaded(location)
}
}

Answer 1

I'm going to assume that a button triggers the segue to the next view. I'm also going to assume that the button is hooked up to a function for target-action. I'm also going to assume that you have the code to get the zip codes, otherwise you'll have to ask a separate question for that.
Assumptions aside, you need to present a UIAlertController instead of going to the next view controller when tapping the button. In order to do that:
func buttonAction() {
if verifyZipCode() {
let alert = UIAlertController(title: "Hold Up", message: "That zip code is invalid.", preferredStyle: .Alert)
let fixIt = UIAlertAction(title: "Fix It!", style: .Default, handler: nil) // handler could also contain code to make text field red or something interesting
alert.addAction(fixIt)
presentViewController(alert, animated: true, completion: nil)
} else {
// existing segue code
}
}
func verifyZipCode() -> Bool {
// Take text field text and verify zip code
}