How do I set a the serverResponse var from within the if let data string statement - swift

Question

func getResponse(serverName: String) -> String {
var serverResponse: String = "No Response"
let serverURL = "http://" + serverName + ":3000"
if let url = URL(string: serverURL) {
URLSession.shared.dataTask(with: url) { data, response, error in
if let data = data {
if let jsonString = String(data: data, encoding: .utf8) {
serverResponse = jsonString
print(jsonString)
}
}
}.resume()
}
return serverResponse
}
I'm trying to set the serverResponse variable from within the if let jsonString but it always returns "No response"(the vars default) and the print function from within the if let jsonString will print out the server response.

Answer 1

DataTask is asynchronous. your function is returning the value before the server request has been completed. You should use a completion handler here.
func getResponse(serverName: String , completion : #escaping (Bool,String?) -> ()) {
let serverURL = "http://" + serverName + ":3000"
if let url = URL(string: serverURL) {
URLSession.shared.dataTask(with: url) { data, response, error in
if let data = data {
if let jsonString = String(data: data, encoding: .utf8) {
print(jsonString)
completion(true,jsonString)
}
} else {
completion(false,nil)
}
}.resume()
}
}
Then you can call the above function like this:
getResponse(serverName: "yourServerName") { (isSuccess, response) in
if isSuccess {
self.serverResponse = response ?? ""
} else {
// your api request failed. show alert or whatever you want to inform the user.
}
}

Answer 2

You need to add a completionHandler.
func getResponse(serverName: String, onCompletion: #escaping (String?) -> Void) {
var serverResponse: String = "No Response"
let serverURL = "http://" + serverName + ":3000"
if let url = URL(string: serverURL) {
URLSession.shared.dataTask(with: url) { data, response, error in
if let data = data {
if let jsonString = String(data: data, encoding: .utf8) {
serverResponse = jsonString
print(jsonString)
onCompletion(serverResponse)
}
}
}.resume()
}
}

Answer 3

Create serverResponse outside the getResponse(serverName:) method and use property observer didSet to observe the changes in serverResponse, i.e.
var serverResponse: String = "No Response" {
didSet {
print("newValue: ", serverResponse)
//add the code here..
}
}
didSet will be called every time there is any change in serverResponse. So, any code that you want to run after getting the serverResponse from API, write here.
Also, no need to return anything from getResponse(serverName:) method. So, the method will now look like,
func getResponse(serverName: String) {
let serverURL = "http://" + serverName + ":3000"
if let url = URL(string: serverURL) {
URLSession.shared.dataTask(with: url) { data, response, error in
if let data = data {
if let jsonString = String(data: data, encoding: .utf8) {
serverResponse = jsonString
print(jsonString)
}
}
}.resume()
}
}