How to return value from a Closure in Swift?

Question

So I am using fabric plugin/Twitter-kit to use twitter api in my application. I want to get the image URL of profile picture of a celebrity. here is my code below.

Answer 1

You need to return from an @escaping closure. Change the function

func getImageURL(celebrity: String) -> String {

}

to

func getImageURL(celebrity: String, completion: @escaping(String)->()) {

      // your code
      completion(imgURL)
}

You can use it as given below

getImageURL(celebrity: String) { (imgURL) in

      self.imgURL = imgURL // Using self as the closure is running in background
}

Here is an example how I write multiple methods with closures for completion.

class ServiceManager: NSObject {

//  Static Instance variable for Singleton
static var sharedSessionManager = ServiceManager()

//  Function to execute GET request and pass data from escaping closure
func executeGetRequest(with urlString: String, completion: @escaping (Data?) -> ()) {

    let url = URL.init(string: urlString)
    let urlRequest = URLRequest(url: url!)

    URLSession.shared.dataTask(with: urlRequest) { (data, response, error) in
        //  Log errors (if any)
        if error != nil {
            print(error.debugDescription)
        } else {
            //  Passing the data from closure to the calling method
            completion(data)
        }
    }.resume()  // Starting the dataTask
}

//  Function to perform a task - Calls executeGetRequest(with urlString:) and receives data from the closure.
func downloadMovies(from urlString: String, completion: @escaping ([Movie]) -> ()) {
    //  Calling executeGetRequest(with:)
    executeGetRequest(with: urlString) { (data) in  // Data received from closure
        do {
            //  JSON parsing
            let responseDict = try JSONSerialization.jsonObject(with: data!, options: .allowFragments) as? [String: Any]
            if let results = responseDict!["results"] as? [[String:Any]] {
                var movies = [Movie]()
                for obj in results {
                    let movie = Movie(movieDict: obj)
                    movies.append(movie)
                }
                //  Passing parsed JSON data from closure to the calling method.
                completion(movies)
            }
        } catch {
            print("ERROR: could not retrieve response")
        }
    }
  }
}

Below is the example how I use it to pass values.

ServiceManager.sharedSessionManager.downloadMovies(from: urlBase) { (movies : [Movie]) in   // Object received from closure
      self.movies = movies
      DispatchQueue.main.async {
            //  Updating UI on main queue
            self.movieCollectionView.reloadData()
      }
}

I hope this helps anybody looking for the same solution.