Generate your own Error code in swift 3

Question

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  amp  amp  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

User · Answer

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

User · Answer

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  amp  helpful to design and work with large software   So  there can be two techniques to handle the code in better way   1  The completion callback will perform all the checks  completionHandler data  httpResponse  responseError     2  Your method decides success and error situation and then invokes corresponding callback  if nil    responseError       successCallback data    else      failureCallback data  responseError     failure can have data also for standard REST request response APIs     Happy coding

User · Answer

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   quot My App Error    quot     func print error  Error        print  quot We have an ERROR   quot   error localizedDescription

User · Answer

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

User · Answer

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  - gt  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

User · Answer

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  - gt  CustomError           return RequestError rawValue  errorCode

User · Answer

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

User · Answer

You should use NSError object   let error   NSError domain     code 401  userInfo   NSLocalizedDescriptionKey   Invalid access token     Then cast NSError to Error object

User · Answer

Details   Xcode Version 10 2 1  10E1001  Swift 5   Solution of organizing errors in an app  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                     Usage    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

User · Answer

You can create a protocol  conforming to the Swift LocalizedError protocol  with these values   protocol OurErrorProtocol  LocalizedError        var title  String    get       var code  Int   get       This then enables us to create concrete errors like so   struct CustomError  OurErrorProtocol        var title  String      var code  Int     var errorDescription  String    return  description       var failureReason  String    return  description        private var  description  String      init title  String   description  String  code  Int            self title   title     Error          self  description   description         self code   code

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