Why my value is not passing into secondViewController [closed] - ios

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I want to pass simple String from oneVC to secondVC. I'm new to iOS.
I declared String nameOfFilm.
When I'm clicking on CollectionViewItem I'm downloading JSON, taking one value of it(String) and assign it to nameOfFilm. Then I'm starting segue to the secondVC.
in the PrepareForSegue method with proper identifier I compare the secondVC value to the nameOfFlim.(nextScene.name = nameOfFilm)
In the result, when the secondVC comes in, nextScene.name is empty.enter image description here
JSON i parsed properly. I think it may be mismatch in time and some functions are too fast. What is causing the problem?
var nameOfFilm = String()
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
INDEX_NUMBER_BEFORE = indexPath.row
let filmID = arrayWithID[INDEX_NUMBER_BEFORE]
downloadFilm(url: "https://api.themoviedb.org/3/movie/\(filmID)\(key)&append_to_response=videos,images")
performSegue(withIdentifier: "toTheDetail", sender: self)
}
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == "toTheDetail" {
let nextScene = segue.destination as! FilmDetailViewController
nextScene.name = nameOfFilm
}
}

Answer 1

The issue here will be that downloadFilm will be an asynchronous task that occurs in the background and takes some time to make the request and respond with the value that you need.
Your downloadFilm function should accept a callback so that you can wait for the response value and then perform an action based on that response, a typical way of using this would be something like:
downloadFilm(url: "https://api.themoviedb.org/3/movie/\(filmID)\(key)&append_to_response=videos,images") { filmName in
self.nameOfFilm = filmName
self.performSegue(withIdentifier: "toTheDetail", sender: self)
}
To do this you would need to update your downloadFilm function, so that its similar to this...
func downloadFilm(url: String, completion: #escaping (_ filmName: String) -> Void) {
// do work here to setup network request
let task = URLSession.shared.dataTask(with: request) { data, response, error in
// parse response and get name
completion(name)
}
}
Here is a guide on Swift completion handlers that will help understand the concept.