Unexpected Non-Void Return Value in Void Function Swift 4 Using JSON Serialisation

Unexpected non-void return value in void function swift 4 using json serialisation

You can't return data directly from an asynchronous task. Use a closure

Create a Function using a closure like.

func jsonSerialisation(jsonUrl: String, completion block: @escaping ((NSArray) -> ())){
    let url = URL(string: JsonUrl)
    let task = URLSession.shared.dataTask(with: url!) { (data, responce, error) in
        if let e = error{
            print(e.localizedDescription)
        }
        else{
            if let content = data{
                do {
                    if let Json = try JSONSerialization.jsonObject(with: content, options: JSONSerialization.ReadingOptions.mutableContainers) as? NSArray{
                        block(Json)
                    }
                }
                catch let error{
                    print(error.localizedDescription)
                }
            }
        }
    }
    task.resume()
}

And Call :

jsonSerialisation(jsonUrl: "Your Url") { (json) in
    print(json)
}

This is helpful

Unexpected non-void return value in void function when returns an array

You can´t just return words in your closure. First of all it´s an async method second you need to return a value outside of the closure which will be called before the closure. You need to have a completionHandler instead of returning Array<Any>. In that case you can pass the value if and when it succeeds. Something like this:

func getWords(onCompletion: @escaping (Array<Any>) -> Void) {
    ref = Database.database().reference()
    ref.child("addedWords").observe(.value, with: { (DataSnapshot) in
        var tempWords = DataSnapshot.value as! [String:AnyObject]
        var words = Array(tempWords.keys)
        print(words)
        onCompletion(words)
    })
}

To call it:

getWords(onCompletion: { (words) in
    print(words)
})

Unexpected non-void return value in void function (Swift 3)

If you are calling an async method like Alamofire.request, then you need notify when this async method is over with closures

Try with this

func postUser(username: String, pass: String, finishedClosured:@escaping ((Bool)->Void))  {
            Alamofire.request("https://someAPI.com/auth/login", method: .post, parameters: ["email": contact, "password": pass], encoding: URLEncoding.default, headers: ["Accept":"application/json"]).responseJSON { (response) in

                switch(response.result) {
                    case .success(let value):
                        let json = JSON(value)
                        print("JSON: \(json)")
                        print(json["data"]["result"])
                        finishedClosured(true)
                    case .failure(let error):
                        print(error)
                        finishedClosured(false)
                }
            }
        }

Use it

 self.postUser(username: "your UserName", pass: "Your Pass") { (result) in
            if(result){
                debugPrint("All is fine")
            }else{
                debugPrint("All is wrong")
            }
        }

Unexpected non-void return value in void function in request to server iOS Swift 3

You have implemented at least two async operations and they are can't return values. For async operations you should use completion handlers like this:

func sendRequest(urlString: String, method: String, completion: @escaping (_ dictionary: NSDictionary?, _ error: Error?) -> Void) {

    DispatchQueue.global(qos: .background).async {
        var request = URLRequest(url: URL(string:urlString)!)
        request.httpMethod = method
        let task = URLSession.shared.dataTask(with: request) { data, response, error in
            guard let data = data, error == nil else {                                                 // check for fundamental networking error
                print("error=\(error)")
                completion(nil, error)
                return
            }

            if let httpStatus = response as? HTTPURLResponse, httpStatus.statusCode != 200 {           // check for http errors
                print("statusCode should be 200, but is \(httpStatus.statusCode)")
                print("response = \(response)")
                // make error here and then
                completion(nil, error)
                return
            }

            let responseString = String(data: data, encoding: .utf8)
            print("responseString = \(responseString)")

            DispatchQueue.main.async {
                do {
                    let jsonDictionary:NSDictionary = try JSONSerialization.jsonObject(with: data, options: []) as! [String: Any] as NSDictionary

                    completion(jsonDictionary, nil)

                } catch {
                    completion(nil, error)
                }
            }

        }

        task.resume()
    }
}

Unexpected non-void return value in void function in request to server iOS Swift 3

You have implemented at least two async operations and they are can't return values. For async operations you should use completion handlers like this:

func sendRequest(urlString: String, method: String, completion: @escaping (_ dictionary: NSDictionary?, _ error: Error?) -> Void) {

    DispatchQueue.global(qos: .background).async {
        var request = URLRequest(url: URL(string:urlString)!)
        request.httpMethod = method
        let task = URLSession.shared.dataTask(with: request) { data, response, error in
            guard let data = data, error == nil else {                                                 // check for fundamental networking error
                print("error=\(error)")
                completion(nil, error)
                return
            }

            if let httpStatus = response as? HTTPURLResponse, httpStatus.statusCode != 200 {           // check for http errors
                print("statusCode should be 200, but is \(httpStatus.statusCode)")
                print("response = \(response)")
                // make error here and then
                completion(nil, error)
                return
            }

            let responseString = String(data: data, encoding: .utf8)
            print("responseString = \(responseString)")

            DispatchQueue.main.async {
                do {
                    let jsonDictionary:NSDictionary = try JSONSerialization.jsonObject(with: data, options: []) as! [String: Any] as NSDictionary

                    completion(jsonDictionary, nil)

                } catch {
                    completion(nil, error)
                }
            }

        }

        task.resume()
    }
}

How do I properly call a non-return-value Swift function when it also has an overloading version that has returned value?

As you discovered, you can guide type inferencing to use the overload that returns Void by suppling a type. The other way to supply a type for type inferencing is to use the as keyword. In your case, it would read doSomething() as Void.

Return struct after parsing json in Swift

I found the solution. You have to add a closure and then use it when calling the function.

func getData(symbol: String, completion: @escaping (Stock) -> Void) {

        let apiURL = "https://cloud.iexapis.com/stable/stock/\(symbol)/quote?token=\(secretToken)"
        let url = URL(string: apiURL)!

        URLSession.shared.dataTask(with: url) { (data, response, err) in

        guard let data = data else { return  }

            do {
                let json = try JSONDecoder().decode(Stock.self, from: data)
                let stockResult = Stock(symbol: json.symbol,
                                        companyName: json.companyName,
                                        latestPrice: json.latestPrice
                )

                //I want to return this Stock structure

                completionBlock(stockResult)

            } catch let jsonErr {
                print("Error serialising json: ", jsonErr)
            }
        }.resume()

    }

then in the main you call

getData(symbol: "aapl") {(output) in
            print(output)
}

How to return value from Alamofire

As mattt points out, Alamofire is returning data asynchronously via a “completion handler” pattern, so you must do the same. You cannot just return the value immediately, but you instead want to change your method to not return anything, but instead use a completion handler closure pattern.

Nowadays, that might look like:

func getOrders(completionHandler: @escaping (Result<[String: Any]>) -> Void) {
    performRequest("orders", completion: completionHandler)
}

func performRequest(_ section: String, completion: @escaping (Result<[String: Any]>) -> Void) {
    let url = baseURL.appendingPathComponent(section)
    let params = ["consumer_key": "key", "consumer_secret": "secret"]

    Alamofire.request(url, parameters: params)
        .authenticate(user: consumerKey, password: consumerSecret)
        .responseJSON { response in
            switch response.result {
            case .success(let value as [String: Any]):
                completion(.success(value))

            case .failure(let error):
                completion(.failure(error))

            default:
                fatalError("received non-dictionary JSON response")
            }
    }
}

Then, when you want to call it, you use this completion closure parameter (in trailing closure, if you want):

api.getOrders { result in
    switch result {
    case .failure(let error):
        print(error)

    case .success(let value):
        // use `value` here
    }
}

// but don't try to use the `error` or `value`, as the above closure
// has not yet been called
//

IOS Swift How can I get value from an Async method

You can use a callback function for that like this:

func GetData(callback: (Int) -> Void) {
    //Inside async task, Once you get the values you want to send in callback
    callback(status)
}

You will get a callback from where you called the function.

For your situation, Anbu's answer will work too.

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