Reflection - get attribute name and value on property

Question

I have a class  lets call it Book with a property called Name  With that property  I have an attribute associated with it   public class Book        Author  AuthorName        public string Name               get  private set             In my main method  I m using reflection and wish to get key value pair of each attribute for each property  So in this example  I d expect to see  Author  for attribute name and  AuthorName  for the attribute value   Question  How do I get the attribute name and value on my properties using Reflection

User · Answer

foreach  var p in model GetType   GetProperties         var valueOfDisplay           p GetCustomAttributesData            Any a   gt  a AttributeType Name     DisplayNameAttribute                  p GetCustomAttribute lt DisplayNameAttribute gt    DisplayName                p Name      In this example I used DisplayName instead of Author because it has a field named  DisplayName  to be shown with a value

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to get attribute from enum  i m using     public enum ExceptionCodes       ExceptionCode 1000     InternalError       public static  int code  string message  Translate ExceptionCodes code                        return code GetType                GetField Enum GetName typeof ExceptionCodes   code                GetCustomAttributes false  Where  attr    gt                                return  attr is ExceptionCodeAttribute                  Select customAttr   gt                                var attr    customAttr as ExceptionCodeAttribute                   return  attr Code  attr FriendlyMessage                  FirstOrDefault                   Using   var  message   Translate code

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I wrote this into a dynamic method since I use lots of attributes throughout my application  Method  public static dynamic GetAttribute Type objectType  string propertyName  Type attrType                  get the property         var property   objectType GetProperty propertyName              check for object relation         return property GetCustomAttributes   FirstOrDefault x   gt  x GetType      attrType          Usage  var objectRelAttr   GetAttribute typeof Person    quot Country quot   typeof ObjectRelationAttribute     var displayNameAttr   GetAttribute typeof Product    quot Category quot   typeof DisplayNameAttribute     Hope this helps anyone

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You can use GetCustomAttributesData   and GetCustomAttributes     var attributeData   typeof Book  GetProperty  Name   GetCustomAttributesData    var attributes   typeof Book  GetProperty  Name   GetCustomAttributes false

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I have solved similar problems by writing a Generic Extension Property Attribute Helper   using System  using System Linq  using System Linq Expressions  using System Reflection   public static class AttributeHelper       public static TValue GetPropertyAttributeValue lt T  TOut  TAttribute  TValue gt           Expression lt Func lt T  TOut gt  gt  propertyExpression           Func lt TAttribute  TValue gt  valueSelector           where TAttribute   Attribute               var expression    MemberExpression  propertyExpression Body          var propertyInfo    PropertyInfo  expression Member          var attr   propertyInfo GetCustomAttributes typeof TAttribute   true  FirstOrDefault   as TAttribute          return attr    null   valueSelector attr    default TValue             Usage   var author   AttributeHelper GetPropertyAttributeValue lt Book  string  AuthorAttribute  string gt  prop   gt  prop Name  attr   gt  attr Author      author    AuthorName

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To get all attributes of a property in a dictionary use this   typeof Book     GetProperty  Name      GetCustomAttributes false      ToDictionary a   gt  a GetType   Name  a   gt  a     remember to change from false to true if you want to include inheritted attributes as well

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private static Dictionary lt string  string gt  GetAuthors         return typeof Book  GetProperties            SelectMany prop   gt  prop GetCustomAttributes             OfType lt AuthorAttribute gt             ToDictionary a   gt  a GetType   Name Replace  quot Attribute quot    quot  quot    a   gt  a Name       Example using generics  target framework 4 5   using System  using System Collections Generic  using System Linq  using System Reflection   private static Dictionary lt string  string gt  GetAttribute lt TAttribute  TType gt       Func lt TAttribute  string gt  valueFunc      where TAttribute   Attribute       return typeof TType  GetProperties            SelectMany p   gt  p GetCustomAttributes             OfType lt TAttribute gt             ToDictionary a   gt  a GetType   Name Replace  quot Attribute quot    quot  quot    valueFunc       Usage  var dictionary   GetAttribute lt AuthorAttribute  Book gt  a   gt  a Name

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Use typeof Book  GetProperties   to get an array of PropertyInfo instances   Then use GetCustomAttributes   on each PropertyInfo to see if any of them have the Author Attribute type   If they do  you can get the name of the property from the property info and the attribute values from the attribute   Something along these lines to scan a type for properties that have a specific attribute type and to return data in a dictionary  note that this can be made more dynamic by passing types into the routine    public static Dictionary lt string  string gt  GetAuthors         Dictionary lt string  string gt   dict   new Dictionary lt string  string gt          PropertyInfo   props   typeof Book  GetProperties        foreach  PropertyInfo prop in props                object   attrs   prop GetCustomAttributes true           foreach  object attr in attrs                        AuthorAttribute authAttr   attr as AuthorAttribute              if  authAttr    null                                string propName   prop Name                  string auth   authAttr Name                    dict Add propName  auth                                      return  dict

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If you just want one specific Attribute value For instance Display Attribute you can use the following code   var pInfo   typeof Book  GetProperty  Name                                 GetCustomAttribute lt DisplayAttribute gt     var name   pInfo Name

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If you mean  for attributes that take one parameter  list the attribute-names and the parameter-value   then this is easier in  NET 4 5 via the CustomAttributeData API   using System Collections Generic  using System ComponentModel  using System Reflection   public static class Program       static void Main                 PropertyInfo prop   typeof Foo  GetProperty  Bar            var vals   GetPropertyAttributes prop              has  DisplayName    abc   Browsable   false           public static Dictionary lt string  object gt  GetPropertyAttributes PropertyInfo property                Dictionary lt string  object gt  attribs   new Dictionary lt string  object gt                look for attributes that takes one constructor argument         foreach  CustomAttributeData attribData in property GetCustomAttributesData                            if attribData ConstructorArguments Count    1                                string typeName   attribData Constructor DeclaringType Name                  if  typeName EndsWith  Attribute    typeName   typeName Substring 0  typeName Length - 9                   attribs typeName    attribData ConstructorArguments 0  Value                                   return attribs           class Foo        DisplayName  abc         Browsable false       public string Bar   get  set

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While the above most upvoted answers definitely work  I d suggest using a slightly different approach in some cases   If your class has multiple properties with always the same attribute and you want to get those attributes sorted into a dictionary  here is how   var dict   typeof Book  GetProperties   ToDictionary p   gt  p Name  p   gt  p GetCustomAttributes typeof AuthorName   false  Select a   gt   AuthorName a  FirstOrDefault       This still uses cast but ensures that the cast will always work as you will only get the custom attributes of the type  AuthorName    If you had multiple Attributes above answers would get a cast exception

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Necromancing   For those that still have to maintain  NET 2 0  or those that want to do it without LINQ   public static object GetAttribute System Reflection MemberInfo mi  System Type t        object   objs   mi GetCustomAttributes t  true        if  objs    null    objs Length  lt  1          return null       return objs 0        public static T GetAttribute lt T gt  System Reflection MemberInfo mi        return  T GetAttribute mi  typeof T        public delegate TResult GetValue t lt in T  out TResult gt  T arg1    public static TValue GetAttributValue lt TAttribute  TValue gt  System Reflection MemberInfo mi  GetValue t lt TAttribute  TValue gt  value  where TAttribute   System Attribute       TAttribute   objAtts    TAttribute   mi GetCustomAttributes typeof TAttribute   true       TAttribute att    objAtts    null    objAtts Length  lt  1    default TAttribute    objAtts 0          TAttribute att    TAttribute GetAttribute mi  typeof TAttribute         if  att    null                return value att             return default TValue       Example usage   System Reflection FieldInfo fi   t GetField  PrintBackground    wkHtmlOptionNameAttribute att   GetAttribute lt wkHtmlOptionNameAttribute gt  fi   string name   GetAttributValue lt wkHtmlOptionNameAttribute  string gt  fi  delegate wkHtmlOptionNameAttribute a   return a Name       or simply   string aname   GetAttributValue lt wkHtmlOptionNameAttribute  string gt  fi  a   gt  a Name

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Just looking for the right place to put this piece of code   let s say you have the following property    Display Name    Solar Radiation  Average    ShortName    SolarRadiationAvg    public int SolarRadiationAvgSensorId   get  set      And you want to get the ShortName value  You can do     DisplayAttribute  typeof SensorsModel  GetProperty SolarRadiationAvgSensorId  GetCustomAttribute typeof DisplayAttribute     ShortName    Or to make it general   internal static string GetPropertyAttributeShortName string propertyName        return   DisplayAttribute  typeof SensorsModel  GetProperty propertyName  GetCustomAttribute typeof DisplayAttribute     ShortName

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Here are some static methods you can use to get the MaxLength  or any other attribute   using System  using System Linq  using System Reflection  using System ComponentModel DataAnnotations  using System Linq Expressions   public static class AttributeHelpers    public static Int32 GetMaxLength lt T gt  Expression lt Func lt T string gt  gt  propertyExpression        return GetPropertyAttributeValue lt T string MaxLengthAttribute Int32 gt  propertyExpression attr   gt  attr Length        Optional Extension method public static Int32 GetMaxLength lt T gt  this T instance Expression lt Func lt T string gt  gt  propertyExpression        return GetMaxLength lt T gt  propertyExpression         Required generic method to get any property attribute from any class public static TValue GetPropertyAttributeValue lt T  TOut  TAttribute  TValue gt  Expression lt Func lt T TOut gt  gt  propertyExpression Func lt TAttribute TValue gt  valueSelector  where TAttribute   Attribute       var expression    MemberExpression propertyExpression Body      var propertyInfo    PropertyInfo expression Member      var attr   propertyInfo GetCustomAttributes typeof TAttribute  true  FirstOrDefault   as TAttribute       if  attr  null            throw new MissingMemberException typeof T  Name     propertyInfo Name typeof TAttribute  Name              return valueSelector attr          Using the static method     var length   AttributeHelpers GetMaxLength lt Player gt  x   gt  x PlayerName     Or using the optional extension method on an instance     var player   new Player    var length   player GetMaxLength x   gt  x PlayerName     Or using the full static method for any other attribute  StringLength for example      var length   AttributeHelpers GetPropertyAttributeValue lt Player string StringLengthAttribute Int32 gt  prop   gt  prop PlayerName attr   gt  attr MaximumLength     Inspired by the Mikael Engver s answer

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public static class PropertyInfoExtensions       public static TValue GetAttributValue lt TAttribute  TValue gt  this PropertyInfo prop  Func lt TAttribute  TValue gt  value  where TAttribute   Attribute               var att   prop GetCustomAttributes              typeof TAttribute   true               FirstOrDefault   as TAttribute          if  att    null                        return value att                     return default TValue             Usage      get class properties with attribute  AuthorAttribute          var props   typeof Book  GetProperties   Where prop   gt  Attribute IsDefined prop  typeof AuthorAttribute                 foreach  var prop in props                               string value   prop GetAttributValue  AuthorAttribute a    gt  a Name                   or      get class properties with attribute  AuthorAttribute          var props   typeof Book  GetProperties   Where prop   gt  Attribute IsDefined prop  typeof AuthorAttribute             IList lt string gt  values   props Select prop   gt  prop GetAttributValue  AuthorAttribute a    gt  a Name   Where attr   gt  attr    null  ToList

[c#] Reflection - get attribute name and value on property

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