What I am trying to achieve is perform a URLSession
request in swift 3. I am performing this action in a separate function (so as not to write the code separately for GET and POST) and returning the URLSessionDataTask
and handling the success and failure in closures. Sort of like this-
let task = URLSession.shared.dataTask(with: request) { (data, uRLResponse, responseError) in
DispatchQueue.main.async {
var httpResponse = uRLResponse as! HTTPURLResponse
if responseError != nil && httpResponse.statusCode == 200{
successHandler(data!)
}else{
if(responseError == nil){
//Trying to achieve something like below 2 lines
//Following line throws an error soo its not possible
//var errorTemp = Error(domain:"", code:httpResponse.statusCode, userInfo:nil)
//failureHandler(errorTemp)
}else{
failureHandler(responseError!)
}
}
}
}
I do not wish to handle the error condition in this function and wish to generate an error using the response code and return this Error to handle it wherever this function is called from. Can anybody tell me how to go about this? Or is this not the "Swift" way to go about handling such situations?
This question is related to
ios
swift3
nsurlsession
I know you have already satisfied with an answer but if you are interested to know the right approach, then this might be helpful for you. I would prefer not to mix http-response error code with the error code in the error object (confused? please continue reading a bit...).
The http response codes are standard error codes about a http response defining generic situations when response is received and varies from 1xx to 5xx ( e.g 200 OK, 408 Request timed out,504 Gateway timeout etc - http://www.restapitutorial.com/httpstatuscodes.html )
The error code in a NSError object provides very specific identification to the kind of error the object describes for a particular domain of application/product/software. For example your application may use 1000 for "Sorry, You can't update this record more than once in a day" or say 1001 for "You need manager role to access this resource"... which are specific to your domain/application logic.
For a very small application, sometimes these two concepts are merged. But they are completely different as you can see and very important & helpful to design and work with large software.
So, there can be two techniques to handle the code in better way:
completionHandler(data, httpResponse, responseError)
if nil == responseError {
successCallback(data)
} else {
failureCallback(data, responseError) // failure can have data also for standard REST request/response APIs
}
Happy coding :)
In your case, the error is that you're trying to generate an Error
instance. Error
in Swift 3 is a protocol that can be used to define a custom error. This feature is especially for pure Swift applications to run on different OS.
In iOS development the NSError
class is still available and it conforms to Error
protocol.
So, if your purpose is only to propagate this error code, you can easily replace
var errorTemp = Error(domain:"", code:httpResponse.statusCode, userInfo:nil)
with
var errorTemp = NSError(domain:"", code:httpResponse.statusCode, userInfo:nil)
Otherwise check the Sandeep Bhandari's answer regarding how to create a custom error type
You should use NSError object.
let error = NSError(domain:"", code:401, userInfo:[ NSLocalizedDescriptionKey: "Invalid access token"])
Then cast NSError to Error object
You can create enums to deal with errors :)
enum RikhError: Error {
case unknownError
case connectionError
case invalidCredentials
case invalidRequest
case notFound
case invalidResponse
case serverError
case serverUnavailable
case timeOut
case unsuppotedURL
}
and then create a method inside enum to receive the http response code and return the corresponding error in return :)
static func checkErrorCode(_ errorCode: Int) -> RikhError {
switch errorCode {
case 400:
return .invalidRequest
case 401:
return .invalidCredentials
case 404:
return .notFound
//bla bla bla
default:
return .unknownError
}
}
Finally update your failure block to accept single parameter of type RikhError :)
I have a detailed tutorial on how to restructure traditional Objective - C based Object Oriented network model to modern Protocol Oriented model using Swift3 here https://learnwithmehere.blogspot.in Have a look :)
Hope it helps :)
let error = NSError(domain:"", code:401, userInfo:[ NSLocalizedDescriptionKey: "Invaild UserName or Password"]) as Error
self.showLoginError(error)
create an NSError object and typecast it to Error ,show it anywhere
private func showLoginError(_ error: Error?) {
if let errorObj = error {
UIAlertController.alert("Login Error", message: errorObj.localizedDescription).action("OK").presentOn(self)
}
}
I still think that Harry's answer is the simplest and completed but if you need something even simpler, then use:
struct AppError {
let message: String
init(message: String) {
self.message = message
}
}
extension AppError: LocalizedError {
var errorDescription: String? { return message }
// var failureReason: String? { get }
// var recoverySuggestion: String? { get }
// var helpAnchor: String? { get }
}
And use or test it like this:
printError(error: AppError(message: "My App Error!!!"))
func print(error: Error) {
print("We have an ERROR: ", error.localizedDescription)
}
import Foundation
enum AppError {
case network(type: Enums.NetworkError)
case file(type: Enums.FileError)
case custom(errorDescription: String?)
class Enums { }
}
extension AppError: LocalizedError {
var errorDescription: String? {
switch self {
case .network(let type): return type.localizedDescription
case .file(let type): return type.localizedDescription
case .custom(let errorDescription): return errorDescription
}
}
}
// MARK: - Network Errors
extension AppError.Enums {
enum NetworkError {
case parsing
case notFound
case custom(errorCode: Int?, errorDescription: String?)
}
}
extension AppError.Enums.NetworkError: LocalizedError {
var errorDescription: String? {
switch self {
case .parsing: return "Parsing error"
case .notFound: return "URL Not Found"
case .custom(_, let errorDescription): return errorDescription
}
}
var errorCode: Int? {
switch self {
case .parsing: return nil
case .notFound: return 404
case .custom(let errorCode, _): return errorCode
}
}
}
// MARK: - FIle Errors
extension AppError.Enums {
enum FileError {
case read(path: String)
case write(path: String, value: Any)
case custom(errorDescription: String?)
}
}
extension AppError.Enums.FileError: LocalizedError {
var errorDescription: String? {
switch self {
case .read(let path): return "Could not read file from \"\(path)\""
case .write(let path, let value): return "Could not write value \"\(value)\" file from \"\(path)\""
case .custom(let errorDescription): return errorDescription
}
}
}
//let err: Error = NSError(domain:"", code: 401, userInfo: [NSLocalizedDescriptionKey: "Invaild UserName or Password"])
let err: Error = AppError.network(type: .custom(errorCode: 400, errorDescription: "Bad request"))
switch err {
case is AppError:
switch err as! AppError {
case .network(let type): print("Network ERROR: code \(type.errorCode), description: \(type.localizedDescription)")
case .file(let type):
switch type {
case .read: print("FILE Reading ERROR")
case .write: print("FILE Writing ERROR")
case .custom: print("FILE ERROR")
}
case .custom: print("Custom ERROR")
}
default: print(err)
}
protocol CustomError : Error {
var localizedTitle: String
var localizedDescription: String
}
enum RequestError : Int, CustomError {
case badRequest = 400
case loginFailed = 401
case userDisabled = 403
case notFound = 404
case methodNotAllowed = 405
case serverError = 500
case noConnection = -1009
case timeOutError = -1001
}
func anything(errorCode: Int) -> CustomError? {
return RequestError(rawValue: errorCode)
}
Implement LocalizedError:
struct StringError : LocalizedError
{
var errorDescription: String? { return mMsg }
var failureReason: String? { return mMsg }
var recoverySuggestion: String? { return "" }
var helpAnchor: String? { return "" }
private var mMsg : String
init(_ description: String)
{
mMsg = description
}
}
Note that simply implementing Error, for instance, as described in one of the answers, will fail (at least in Swift 3), and calling localizedDescription will result in the string "The operation could not be completed. (.StringError error 1.)"
Source: Stackoverflow.com