How do I read an attribute on a class at runtime

Question

I am trying to create a generic method that will read an attribute on a class and return that value at runtime  How do would I do this      Note  DomainName attribute is of class DomainNameAttribute     DomainName  MyTable    Public class MyClass   DomainBase      What I am trying to generate      This should return  MyTable  String DomainNameValue   GetDomainName lt MyClass gt

User · Answer

There is already an extension to do this.

namespace System.Reflection
{
    // Summary:
    //     Contains static methods for retrieving custom attributes.
    public static class CustomAttributeExtensions
    {
        public static T GetCustomAttribute<T>(this MemberInfo element, bool inherit) where T : Attribute;
    }
}

So:

var attr = typeof(MyClass).GetCustomAttribute<DomainNameAttribute>(false);
return attr != null ? attr.DomainName : "";

User · Answer

When you have Overridden Methods with same Name Use the helper below   public static TValue GetControllerMethodAttributeValue lt T  TT  TAttribute  TValue gt  this T type  Expression lt Func lt T  TT gt  gt  exp  Func lt TAttribute  TValue gt  valueSelector  where TAttribute   Attribute                       var memberExpression   exp  Body as MethodCallExpression               if  memberExpression Method GetCustomAttributes typeof TAttribute   false  FirstOrDefault   is TAttribute attr  amp  amp  valueSelector    null                                return valueSelector attr                              return default TValue                  Usage  var someController   new SomeController Some params   var str     typeof SomeController  GetControllerMethodAttributeValue x      someController SomeMethod It IsAny      RouteAttribute   routeAttribute     routeAttribute Template

User · Answer

System Reflection MemberInfo info   typeof MyClass   object   attributes   info GetCustomAttributes true    for  int i   0  i  lt  attributes Length  i          if  attributes i  is DomainNameAttribute                System Console WriteLine   DomainNameAttribute  attributes i   Name

User · Answer

Simplified Generic version   Shared Function GetAttribute Of TAttribute  info As MemberInfo  As TAttribute     Return info GetCustomAttributes GetType TAttribute                                         False  FirstOrDefault   End Function    Example usage over PropertyInfo Dim fieldAttr   GetAttribute Of DataObjectFieldAttribute  pInfo  If fieldAttr IsNot Nothing AndAlso fieldAttr PrimaryKey Then     keys Add pInfo Name  End If   Probably just as easy to use the body of generic function inline  It doesn t make any sense to me to make the function generic over the type MyClass   string DomainName   GetAttribute lt DomainNameAttribute gt  typeof MyClass   Name    null reference exception if MyClass doesn t have the attribute

User · Answer

In case anyone needs a nullable result and for this to work across Enums  PropertyInfo and classes  here s how I solved it   This is a modification of Darin Dimitrov s updated solution   public static object GetAttributeValue lt TAttribute  TValue gt  this object val  Func lt TAttribute  TValue gt  valueSelector  where TAttribute   Attribute       try               Type t   val GetType            TAttribute attr          if  t IsEnum  amp  amp  t GetField val ToString    GetCustomAttributes typeof TAttribute   true  FirstOrDefault   is TAttribute att                           Applies to Enum values             attr   att                    else if  val is PropertyInfo pi  amp  amp  pi GetCustomAttributes typeof TAttribute   true  FirstOrDefault   is TAttribute piAtt                           Applies to Properties in a Class             attr   piAtt                    else                          Applies to classes             attr    TAttribute t GetCustomAttributes typeof TAttribute   false  FirstOrDefault                      return valueSelector attr             catch               return null            Usage examples      Class SettingsEnum SettingGroup settingGroup    SettingsEnum SettingGroup  this GetAttributeValue  SettingGroupAttribute attr    gt  attr Value  as SettingsEnum SettingGroup        Enum DescriptionAttribute desc   settingGroup GetAttributeValue  DescriptionAttribute attr    gt  attr  as DescriptionAttribute      PropertyInfo        foreach  PropertyInfo pi in this GetType   GetProperties          string setting     SettingsEnum SettingName  pi GetAttributeValue  SettingNameAttribute attr    gt  attr Value  as SettingsEnum SettingName    ToString

User · Answer

Rather then write a lot of code  just do this                 dynamic tableNameAttribute   typeof T  CustomAttributes FirstOrDefault   ToString       dynamic tableName   tableNameAttribute Substring tableNameAttribute LastIndexOf       tableNameAttribute LastIndexOf

User · Answer

I used Darin Dimitrov s answer to create a generic extension to get member attributes for any member in a class  instead of attributes for a class   I m posting it here because others may find it useful   public static class AttributeExtensions            lt summary gt          Returns the value of a member attribute for any member in a class               a member is a Field  Property  Method  etc                  lt remarks gt          If there is more than one member of the same name in the class  it will return the first one  this applies to overloaded methods           lt  remarks gt           lt example gt          Read System ComponentModel Description Attribute from method  MyMethodName  in class  MyClass                var Attribute   typeof MyClass  GetAttribute  MyMethodName    DescriptionAttribute d    gt  d Description            lt  example gt           lt param name  type  gt The class that contains the member as a type lt  param gt           lt param name  MemberName  gt Name of the member in the class lt  param gt           lt param name  valueSelector  gt Attribute type and property to get  will return first instance if there are multiple attributes of the same type  lt  param gt           lt param name  inherit  gt true to search this member s inheritance chain to find the attributes  otherwise  false  This parameter is ignored for properties and events lt  param gt           lt  summary gt          public static TValue GetAttribute lt TAttribute  TValue gt  this Type type  string MemberName  Func lt TAttribute  TValue gt  valueSelector  bool inherit   false  where TAttribute   Attribute               var att   type GetMember MemberName  FirstOrDefault   GetCustomAttributes typeof TAttribute   inherit  FirstOrDefault   as TAttribute          if  att    null                        return valueSelector att                     return default TValue             Usage example     Read System ComponentModel Description Attribute from method  MyMethodName  in class  MyClass  var Attribute   typeof MyClass  GetAttribute  MyMethodName    DescriptionAttribute d    gt  d Description

User · Answer

A simplified version of Darin Dimitrov s first solution   public string GetDomainName lt T gt          var dnAttribute   typeof T  GetCustomAttribute lt DomainNameAttribute gt  true       if  dnAttribute    null                return dnAttribute Name            return null

User · Answer

public string GetDomainName lt T gt          var dnAttribute   typeof T  GetCustomAttributes          typeof DomainNameAttribute   true       FirstOrDefault   as DomainNameAttribute      if  dnAttribute    null                return dnAttribute Name            return null        UPDATE   This method could be further generalized to work with any attribute   public static class AttributeExtensions       public static TValue GetAttributeValue lt TAttribute  TValue gt           this Type type           Func lt TAttribute  TValue gt  valueSelector           where TAttribute   Attribute               var att   type GetCustomAttributes              typeof TAttribute   true           FirstOrDefault   as TAttribute          if  att    null                        return valueSelector att                     return default TValue             and use like this   string name   typeof MyClass       GetAttributeValue  DomainNameAttribute dna    gt  dna Name

[c#] How do I read an attribute on a class at runtime?

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