function return too early - swift

Question

Can anyone explain why the completion returns empty array?
The function:
import Foundation
class IMBD{
func searchMovies(searchText:String, completion: (result: [Movies]) -> Void){
var movies = [Movies]()
let replacedMovieTitle = searchText.stringByReplacingOccurrencesOfString(" ", withString: "+")
let URLString = "http://www.omdbapi.com/?s=\(replacedMovieTitle)&y=&r=json"
let URL = NSURL(string: URLString)
let session = NSURLSession.sharedSession()
let task = session.dataTaskWithURL(URL!, completionHandler: {(data, response, error) -> Void in
do{
let jsonData = try NSJSONSerialization.JSONObjectWithData(data!, options: .MutableContainers) as! NSDictionary
if let search = jsonData["Search"] as? [[String : AnyObject]]{
for hit in search{
guard let title = hit["Title"] as? String else{
print("returna title")
return
}
guard let year = hit["Year"] as? String else{
print("returna year")
return
}
guard let imbdID = hit["imdbID"] as? String else{
print("returna imbd")
return
}
guard let poster = hit["Poster"] as? String else{
print("returna poster")
return
}
let movie = Movies(title: title, released: year, poster: poster, imbdID: imbdID)
movies.append(movie)
}
}
}catch{
}
}).resume()
completion(result: movies)
}
}
The call:
imbd.searchMovies(searchtext!, completion: { (result) -> Void in
self.movieList = result
})

Answer 1

You have to call your completion handles inside the dataTaskWithURL closure, not after it. This runs asynchronously, so if you call your completion outside of the closure, it would be called before the asynchronous request had a chance to retrieve anything.
Also, remember that this closure doesn't run on the main thread, so you likely want to also dispatch this to the main queue (from within the dataTaskWithURL).
For example:
class IMDB {
func searchMovies(searchText:String, completion: (result: [Movie]?, error: NSError?) -> Void) -> NSURLSessionTask {
var movies = [Movie]()
let allowedCharacters = NSCharacterSet.alphanumericCharacterSet().mutableCopy() as! NSMutableCharacterSet
allowedCharacters.addCharactersInString("-._* ")
let replacedMovieTitle = searchText.stringByAddingPercentEncodingWithAllowedCharacters(allowedCharacters)!
.stringByReplacingOccurrencesOfString(" ", withString: "+")
let URLString = "http://www.omdbapi.com/?s=\(replacedMovieTitle)&y=&r=json"
let URL = NSURL(string: URLString)
let session = NSURLSession.sharedSession()
let task = session.dataTaskWithURL(URL!) { data, response, error in
guard error == nil && data != nil else {
dispatch_async(dispatch_get_main_queue()) {
completion(result: nil, error: error)
}
return
}
do {
let jsonData = try NSJSONSerialization.JSONObjectWithData(data!, options: .MutableContainers) as! NSDictionary
if let search = jsonData["Search"] as? [[String : AnyObject]]{
for hit in search{
guard let title = hit["Title"] as? String else{
print("returna title")
continue
}
guard let year = hit["Year"] as? String else{
print("returna year")
continue
}
guard let imdbID = hit["imdbID"] as? String else{
print("returna imbd")
continue
}
guard let poster = hit["Poster"] as? String else{
print("returna poster")
continue
}
let movie = Movie(title: title, released: year, poster: poster, imdbID: imdbID)
movies.append(movie)
}
}
dispatch_async(dispatch_get_main_queue()) {
completion(result: movies, error: nil)
}
} catch let error as NSError {
dispatch_async(dispatch_get_main_queue()) {
completion(result: nil, error: error)
}
}
}
task.resume()
return task
}
}
A couple of other changes in the above code snippet include:
Add guard in case there was a fundamental network error (e.g. remote server down, no Internet access, etc.)
In the guard statements that are checking for nil values, rather than performing a return (in which case no further results will be gathered), you might want to just continue (i.e. skip to the next record). You generally see guard in conjunction with return, but in this case, continue is probably more appropriate.
Frankly, you might want to take this a step further and consider whether some of these might be optional, rather than discarding the whole record. Notably, poster strikes me as something that might be nil if there was no poster available. Maybe some of the others should be optional, too, (e.g. if a movie hasn't been released yet, might it not have a release date?).
The occurrences of "imbd" have been replaced with "imdb".
The Movies class has been renamed to Movie (since each instance is a single movie, not a collection of them).
I changed the completion block to make [Movie] optional and to return the NSError. Without that, you don't have a way to differentiate between "couldn't find a title of that name" and "whoops, something went wrong".
When we call the completion closure from within the dataTaskWithURL, it can be very useful to have searchMovies dispatch completion calls back to the main queue, like above. This is because UI updates must always happen on the main thread, and frequently when you write routines like this, it is so you can update UI or the model with results.
This is not always necessary to do it like this (you might want to just have this call completion directly from the background thread and let the routine that called searchMovies manually dispatch stuff to the main thread itself), but I often find it useful to have this search method just dispatch the completion back to the main thread and be done with it.
As a matter of practice, I always return the NSURLSessionTask when performing requests. You might not need it now, but at some future date, you might want the ability to cancel an on-going request, and having a reference to the task can be useful. It doesn't hurt to return it, and it can be useful.
You probably should be percent escaping the values you add to the URL. Notably the presence of & or + characters could be problematic. Note, in this case, it looks like this site isn't handling it appropriately, anyway, but it's good to get in the habit of properly percent-escaping values in a query.
Personally, I keep this percent escaping logic in a String extension, but I wanted to keep this simple, so I embedded it right in this method, but hopefully it illustrates the idea.