Execute code first! Swift - ios

Question

guys I am getting data from Foursquare APi and here is my code below.
But I am getting a nil error at cellForRowAtIndexPath that venueItems is nil
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
// Table View
self.tableView = UITableView()
// Location Manager Stuff
self.locationManager = CLLocationManager()
self.locationManager.desiredAccuracy = kCLLocationAccuracyNearestTenMeters
self.locationManager.delegate = self
let status = CLLocationManager.authorizationStatus()
if status == .notDetermined {
self.locationManager.requestWhenInUseAuthorization()
} else if status == CLAuthorizationStatus.authorizedWhenInUse
|| status == CLAuthorizationStatus.authorizedAlways {
self.locationManager.startUpdatingLocation()
} else {
showNoPermissionsAlert()
}
exploreVenues()
}
// Func's
func exploreVenues() {
guard let location = self.locationManager.location else {
return
}
var parameters = [Parameter.query: "Pubs"]
parameters += location.parameters()
let task = self.session.venues.explore(parameters) {
(result) -> Void in
if self.venueItems != nil {
return
}
if !Thread.isMainThread {
fatalError("!!!")
}
if let response = result.response {
if let groups = response["groups"] as? [[String: AnyObject]] {
var venues = [[String: AnyObject]]()
for group in groups {
if let items = group["items"] as? [[String: AnyObject]] {
venues += items
}
}
self.venueItems = venues
}
self.tableView.reloadData()
} else if let error = result.error, !result.isCancelled() {
self.showErrorAlert(error)
}
}
task.start()
}
// Table View Data source
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
if let venueItems = self.venueItems {
return venueItems.count
}
return 10
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath) as! VenueTableViewCell
// This is where the error occurs
let item = self.venueItems![(indexPath as NSIndexPath).row] as JSONParameters!
self.configureCellWithItem(cell, item: item!)
return cell
}
func configureCellWithItem(_ cell: VenueTableViewCell, item: JSONParameters) {
if let venueInfo = item["venue"] as? JSONParameters {
cell.nameLabel.text = venueInfo["name"] as? String
}
}
func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
let cell = cell as! VenueTableViewCell
let tips = self.venueItems![(indexPath as NSIndexPath).row]["tips"] as? [JSONParameters]
guard let tip = tips?.first, let user = tip["user"] as? JSONParameters,
let photo = user["photo"] as? JSONParameters else {
return
}
let URL = photoURLFromJSONObject(photo)
if let imageData = session.cachedImageDataForURL(URL) {
cell.venueImageView.image = UIImage(data: imageData)
} else {
cell.venueImageView.image = nil
session.downloadImageAtURL(URL) { (imageData, error) -> Void in
let cell = tableView.cellForRow(at: indexPath) as? VenueTableViewCell
if let cell = cell, let imageData = imageData {
let image = UIImage(data: imageData)
cell.venueImageView.image = image
}
}
}
}
}
I am quite new to programming personally I think that the venueItems is nil because the cellForRowAtIndexPath is being executed first. If this is the error how can I fix it so the code in cellForRowAtIndexpath runs after my venueItems has a value.. or any other more efficient Way?

Answer 1

Your numberOfRowsInSection returns 10 when self.venueItems is nil. self.venueItems appears to be nil until your network request finishes so the table view, having been told it has 10 rows to display asks for a cell for each row. You then attempt to force unwrap an optional property (self.venueItems!) and crash.
It looks like your self.venueItems is an optional for good reason, don't discard that information with a force unwrap (!). You could either return 0 rows when this property is nil or initialize it to a non-optional empty array which you could then always ask for its count.
In general with this sort of problem you don't want to focus on preventing cellForRowAtIndexPath from being called but rather plan for it to be called at any point and return a reasonable result (like reporting that the table has 0 rows) when your background tasks haven't finished yet.