data with request completionhandler not always called - ios

Question

I am making an app where you can search for movies with the API of http://www.omdbapi.com/.
The problem I am having is with the completion handler of dataTaskWithRequest. If you click on one of the collectionView cell, you will go to the detailView of that selected movie. However it doesn't work all the time. I get an error saying: unexpectedly found nil while unwrapping. And that's because it doesn't go in the completion handler of dataTaskWithRequest but goes straight to the detailVC and try passing data in the title label, genre label, etc but there is no data.
I hope you guys know what the problem is, because I have tried and I don't see what the problem is.
Or, does this problem occurs because of something before? Because first I retrieve data from http://www.omdbapi.com/ using "by search" instead of "by ID". And from there I retrieve the ID and from that ID I retrieve data for my detailVC.
Here is my code:
// Go to detail view of selected movie
func collectionView(collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath) {
let selectedMovieId = self.IDs[indexPath.row]
chosenMovieId = selectedMovieId
self.performSegueWithIdentifier("showDetail", sender: self)
}
// Preparations before going to the detail view of selected movie
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
if segue.identifier == "showDetail" {
_ = self.movieInfoFrom(searchMovie: chosenMovieId, segue: segue)
}
}
func movieInfoFrom(searchMovie movieId: String, segue: UIStoryboardSegue) {
let movieUrlString = "http://www.omdbapi.com/?i=\(movieId)&y=&plot=full&r=json"
let url = NSURL(string: movieUrlString)
print(movieUrlString)
let urlRequest = NSURLRequest(URL: url!)
let urlSession = NSURLSession(configuration: NSURLSessionConfiguration.defaultSessionConfiguration())
let urlTask = urlSession.dataTaskWithRequest(urlRequest) { (data, response, error) in
if error == nil {
// Convert data to JSON
let swiftyJSON = JSON(data: data!)
let title = swiftyJSON["Title"].string!
let runTime = swiftyJSON["Runtime"].string!
let genre = swiftyJSON["Genre"].string!
let plot = swiftyJSON["Plot"].string!
let rating = swiftyJSON["imdbRating"].string!
let year = swiftyJSON["Year"].string!
let poster = swiftyJSON["Poster"].string
self.infoResult = ["\(title)", "\(runTime)", "\(genre)", "\(plot)", "\(rating)", "\(year)"]
print("\(self.infoResult)")
let destinationVC = segue.destinationViewController as! MovieDetailController
destinationVC.movieDetails = self.infoResult
destinationVC.moviePoster = poster
}
}
urlTask.resume()
}

Answer 1

I tried to fix your code and explain with some comments:
func collectionView(collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath) {
let selectedMovieId = self.IDs[indexPath.row]
chosenMovieId = selectedMovieId
self.movieInfoFrom(searchMovie: chosenMovieId)
}
// Preparations before going to the detail view of selected movie
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
if segue.identifier == "showDetail" {
let destinationVC = segue.destinationViewController as! MovieDetailController
destinationVC.movieDetails = self.infoResult
destinationVC.moviePoster = poster
}
}
func movieInfoFrom(searchMovie movieId: String) {
let movieUrlString = "http://www.omdbapi.com/?i=\(movieId)&y=&plot=full&r=json"
let url = NSURL(string: movieUrlString)
print(movieUrlString)
let urlRequest = NSURLRequest(URL: url!)
let urlSession = NSURLSession(configuration: NSURLSessionConfiguration.defaultSessionConfiguration())
// This is asynchronously, you can put a loading here
let urlTask = urlSession.dataTaskWithRequest(urlRequest) { (data, response, error) in
// Got response, stop loading here
if error == nil {
// Convert data to JSON
let swiftyJSON = JSON(data: data!)
let title = swiftyJSON["Title"].string!
let runTime = swiftyJSON["Runtime"].string!
let genre = swiftyJSON["Genre"].string!
let plot = swiftyJSON["Plot"].string!
let rating = swiftyJSON["imdbRating"].string!
let year = swiftyJSON["Year"].string!
// You can save the poster as local variable
let poster = swiftyJSON["Poster"].string
self.infoResult = ["\(title)", "\(runTime)", "\(genre)", "\(plot)", "\(rating)", "\(year)"]
print("\(self.infoResult)")
// This should be call on main thread
dispatch_async(dispatch_get_main_queue()) {
self.performSegueWithIdentifier("showDetail", sender: self)
}
}
}
urlTask.resume()
}

Answer 2

Try this code, with safe optionals
func collectionView(collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath) {
chosenMovieId = self.IDs[indexPath.row]
movieInfoFrom(searchMovie: chosenMovieId)
}
func movieInfoFrom(searchMovie movieId: String) {
let movieUrlString = "http://www.omdbapi.com/?i=\(movieId)&y=&plot=full&r=json"
let url = NSURL(string: movieUrlString)
print(movieUrlString)
let urlRequest = NSURLRequest(URL: url!)
let urlSession = NSURLSession(configuration: NSURLSessionConfiguration.defaultSessionConfiguration())
let urlTask = urlSession.dataTaskWithRequest(urlRequest) { (data, response, error) in
if error == nil && data != nil {
// Convert data to JSON
let swiftyJSON = JSON(data: data!)
let title = swiftyJSON["Title"].string ?? ""
let runTime = swiftyJSON["Runtime"].string ?? ""
let genre = swiftyJSON["Genre"].string ?? ""
let plot = swiftyJSON["Plot"].string ?? ""
let rating = swiftyJSON["imdbRating"].string ?? ""
let year = swiftyJSON["Year"].string ?? ""
let poster = swiftyJSON["Poster"].string
self.infoResult = ["\(title)", "\(runTime)", "\(genre)", "\(plot)", "\(rating)", "\(year)"]
print("\(self.infoResult)")
dispatch_async(dispatch_get_main_queue()) {
self.performSegueWithIdentifier("showDetail", sender: poster)
}
}
}
urlTask.resume()
}
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
if segue.identifier == "showDetail", let destinationVC = segue.destinationViewController as? MovieDetailController {
destinationVC.movieDetails = self.infoResult
destinationVC.moviePoster = sender as? String
}
}