How to TryParse for Enum value

Question

I want to write a function which can validate a given value  passed as a string  against possible values of an enum  In the case of a match  it should return the enum instance  otherwise  it should return a default value   The function may not internally use try catch  which excludes using Enum Parse  which throws an exception when given an invalid argument   I d like to use something along the lines of a TryParse function to implement this   public static TEnum ToEnum lt TEnum gt  this string strEnumValue  TEnum defaultValue       object enumValue     if   TryParse  typeof  TEnum   strEnumValue  out enumValue               return defaultValue          return  TEnum  enumValue

User · Answer

There s currently no out of the box Enum TryParse  This has been requested on Connect  Still no Enum TryParse  and got a response indicating possible inclusion in the next framework after  NET 3 5  You ll have to implement the suggested workarounds for now

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The only way to avoid exception handling is to use the GetNames   method  and we all know that  exceptions shouldn t be abused for common application logic

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enum EnumStatus       NAO INFORMADO   0      ENCONTRADO   1      BLOQUEADA PELO ENTREGADOR   2      DISPOSITIVO DESABILITADO   3      ERRO INTERNO   4      AGARDANDO   5          if  Enum TryParse lt EnumStatus gt  item status  out status

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Here is a custom implementation of EnumTryParse  Unlike other common implementations  it also supports enum marked with the Flags attribute            lt summary gt          Converts the string representation of an enum to its Enum equivalent value  A return value indicates whether the operation succeeded          This method does not rely on Enum Parse and therefore will never raise any first or second chance exception           lt  summary gt           lt param name  type  gt The enum target type  May not be null  lt  param gt           lt param name  input  gt The input text  May be null  lt  param gt           lt param name  value  gt When this method returns  contains Enum equivalent value to the enum contained in input  if the conversion succeeded  lt  param gt           lt returns gt          true if s was converted successfully  otherwise  false           lt  returns gt      public static bool EnumTryParse Type type  string input  out object value                if  type    null              throw new ArgumentNullException  type             if   type IsEnum              throw new ArgumentException null   type             if  input    null                        value   Activator CreateInstance type               return false                     input   input Trim            if  input Length    0                        value   Activator CreateInstance type               return false                     string   names   Enum GetNames type           if  names Length    0                        value   Activator CreateInstance type               return false                     Type underlyingType   Enum GetUnderlyingType type           Array values   Enum GetValues type              some enums like System CodeDom MemberAttributes  are  flags but are not declared with Flags            if    type IsDefined typeof FlagsAttribute   true    amp  amp   input IndexOfAny  enumSeperators   lt  0               return EnumToObject type  underlyingType  names  values  input  out value               multi value enum         string   tokens   input Split  enumSeperators  StringSplitOptions RemoveEmptyEntries           if  tokens Length    0                        value   Activator CreateInstance type               return false                     ulong ul   0          foreach  string tok in tokens                        string token   tok Trim       NOTE  we don t consider empty tokens as errors             if  token Length    0                  continue               object tokenValue              if   EnumToObject type  underlyingType  names  values  token  out tokenValue                                 value   Activator CreateInstance type                   return false                             ulong tokenUl              switch  Convert GetTypeCode tokenValue                                 case TypeCode Int16                  case TypeCode Int32                  case TypeCode Int64                  case TypeCode SByte                      tokenUl    ulong Convert ToInt64 tokenValue  CultureInfo InvariantCulture                       break                     case TypeCode Byte                    case TypeCode UInt16                    case TypeCode UInt32                    case TypeCode UInt64                  default                      tokenUl   Convert ToUInt64 tokenValue  CultureInfo InvariantCulture                       break                             ul    tokenUl                    value   Enum ToObject type  ul           return true             private static char    enumSeperators   new char                                     private static object EnumToObject Type underlyingType  string input                if  underlyingType    typeof int                         int s              if  int TryParse input  out s                   return s                     if  underlyingType    typeof uint                         uint s              if  uint TryParse input  out s                   return s                     if  underlyingType    typeof ulong                         ulong s              if  ulong TryParse input  out s                   return s                     if  underlyingType    typeof long                         long s              if  long TryParse input  out s                   return s                     if  underlyingType    typeof short                         short s              if  short TryParse input  out s                   return s                     if  underlyingType    typeof ushort                         ushort s              if  ushort TryParse input  out s                   return s                     if  underlyingType    typeof byte                         byte s              if  byte TryParse input  out s                   return s                     if  underlyingType    typeof sbyte                         sbyte s              if  sbyte TryParse input  out s                   return s                     return null             private static bool EnumToObject Type type  Type underlyingType  string   names  Array values  string input  out object value                for  int i   0  i  lt  names Length  i                          if  string Compare names i   input  StringComparison OrdinalIgnoreCase     0                                value   values GetValue i                   return true                                   if   char IsDigit input 0       input 0      -        input 0                                 object obj   EnumToObject underlyingType  input               if  obj    null                                value   Activator CreateInstance type                   return false                            value   obj              return true                     value   Activator CreateInstance type           return false

User · Answer

Based on  NET 4 5   Sample code below  using System   enum Importance       None      Low      Medium      Critical    class Program       static void Main                The input value      string value    Medium           An unitialized variable      Importance importance          Call Enum TryParse method      if  Enum TryParse value  out importance                    We now have an enum type          Console WriteLine importance    Importance Medium                   Reference   http   www dotnetperls com enum-parse

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In the end you have to implement this around Enum GetNames   public bool TryParseEnum lt T gt  string str  bool caseSensitive  out T value  where T   struct          Can t make this a type constraint        if   typeof T  IsEnum            throw new ArgumentException  Type parameter must be an enum              var names   Enum GetNames typeof T        value    Enum GetValues typeof T   as T    0       For want of a better default     foreach  var name in names            if  String Equals name  str  caseSensitive   StringComparison Ordinal   StringComparison OrdinalIgnoreCase                 value    T Enum Parse typeof T   name               return true                      return false      Additional notes    Enum TryParse is included in  NET 4  See here http   msdn microsoft com library dd991876 VS 100  aspx Another approach would be to directly wrap Enum Parse catching the exception thrown when it fails  This could be faster when a match is found  but will likely to slower if not  Depending on the data you are processing this may or may not be a net improvement      EDIT  Just seen a better implementation on this  which caches the necessary information  http   damieng com blog 2010 10 17 enums-better-syntax-improved-performance-and-tryparse-in-net-3-5

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Have a look at the Enum class  struct     itself   There is a Parse method on that but I m not sure about a tryparse

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Is caching a dynamically generated function dictionary permissable   Because you don t  appear to  know the type of the enum ahead of time  the first execution could generate something subsequent executions could take advantage of   You could even cache the result of Enum GetNames    Are you trying to optimize for CPU or Memory   Do you really need to

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This method will convert a type of enum     public static TEnum ToEnum lt TEnum gt  object EnumValue  TEnum defaultValue                if   Enum IsDefined typeof TEnum   EnumValue                         Type enumType   Enum GetUnderlyingType typeof TEnum                if   EnumValue GetType      enumType                                 string name   Enum GetName typeof HLink ViewModels ClaimHeaderViewModel ClaimStatus   EnumValue                   if  name    null                      return  TEnum Enum Parse typeof TEnum   name                   return defaultValue                                  return  TEnum Enum Parse typeof TEnum   EnumValue ToString              It checks the underlying type and get the name against it to parse  If everything fails it will return default value

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Enum IsDefined will get things done  It may not be as efficient as a TryParse would probably be  but it will work without exception handling   public static TEnum ToEnum lt TEnum gt  this string strEnumValue  TEnum defaultValue        if   Enum IsDefined typeof TEnum   strEnumValue           return defaultValue       return  TEnum Enum Parse typeof TEnum   strEnumValue       Worth noting  a TryParse method was added in  NET 4 0

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There is not a TryParse because the Enum s type is not known until runtime  A TryParse that follows the same methodology as say the Date TryParse method would throw an implicit conversion error on the ByRef parameter   I suggest doing something like this     1 line call to get value MyEnums enumValue    Sections EnumValue typeof Sections   myEnumTextValue  MyEnums SomeEnumDefault      Put this somewhere where you can reuse public static object EnumValue System Type enumType  string value  object NotDefinedReplacement        if  Enum IsDefined enumType  value             return Enum Parse enumType  value         else           return Enum Parse enumType  NotDefinedReplacement

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I have an optimised implementation you could use in UnconstrainedMelody  Effectively it s just caching the list of names  but it s doing so in a nice  strongly typed  generically constrained way

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As others already said  if you don t use Try amp Catch  you need to use IsDefined or GetNames    Here are some samples   they basically are all the same  the first one handling nullable enums  I prefer the 2nd one as it s an extension on strings  not enums   but you can mix them as you want    www objectreference net post Enum-TryParse-Extension-Method aspx flatlinerdoa spaces live com blog cns 17124D03A9A052B0 605 entry mironabramson com blog post 2008 03 Another-version-for-the-missing-method-EnumTryParse aspx lazyloading blogspot com 2008 04 enumtryparse-with-net-35-extension html

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As others have said  you have to implement your own TryParse  Simon Mourier is providing a full implementation which takes care of everything   If you are using bitfield enums  i e  flags   you also have to handle a string like  MyEnum Val1 MyEnum Val2  which is a combination of two enum values  If you just call Enum IsDefined with this string  it will return false  even though Enum Parse handles it correctly   Update  As mentioned by Lisa and Christian in the comments  Enum TryParse is now available for C  in  NET4 and up   MSDN Docs

[c#] How to TryParse for Enum value?

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