Can attributes be added dynamically in C

Question

Is it possible to add attributes at runtime or to change the value of an attribute at runtime

User · Answer

No  it s not   Attributes are meta-data and stored in binary-form in the compiled assembly  that s also why you can only use simple types in them

User · Answer

Attributes are static metadata  Assemblies  modules  types  members  parameters  and return values aren t first-class objects in C   e g   the System Type class is merely a reflected representation of a type   You can get an instance of an attribute for a type and change the properties if they re writable but that won t affect the attribute as it is applied to the type

User · Answer

Well  just to be different  I found an article that references using Reflection Emit to do so     Here s the link  http   www codeproject com KB cs dotnetattributes aspx   you will also want to look into some of the comments at the bottom of the article  because possible approaches are discussed

User · Answer

I don t believe so   Even if I m wrong  the best you can hope for is adding them to an entire Type  never an instance of a Type

User · Answer

In Java I used to work around this by using a map and implementing my own take on Key-Value coding   http   developer apple com documentation Cocoa Conceptual KeyValueCoding KeyValueCoding html

User · Answer

I tried very hard with System ComponentModel TypeDescriptor without success  That does not means it can t work but I would like to see code for that   In counter part  I wanted to change some Attribute values  I did 2 functions which work fine for that purpose                                                                                               public static void SetObjectPropertyDescription this Type typeOfObject  string propertyName   string description                        PropertyDescriptor pd   TypeDescriptor GetProperties typeOfObject  propertyName               var att   pd Attributes typeof DescriptionAttribute   as DescriptionAttribute              if  att    null                                var fieldDescription   att GetType   GetField  description   BindingFlags NonPublic   BindingFlags Instance                   if  fieldDescription    null                                        fieldDescription SetValue att  description                                                                                                                                          public static void SetPropertyAttributReadOnly this Type typeOfObject  string propertyName  bool isReadOnly                        PropertyDescriptor pd   TypeDescriptor GetProperties typeOfObject  propertyName               var att   pd Attributes typeof ReadOnlyAttribute   as ReadOnlyAttribute              if  att    null                                var fieldDescription   att GetType   GetField  isReadOnly   BindingFlags NonPublic   BindingFlags Instance                   if  fieldDescription    null                                        fieldDescription SetValue att  isReadOnly

User · Answer

Why do you need to  Attributes give extra information for reflection  but if you externally know which properties you want you don t need them   You could store meta data externally relatively easily in a database or resource file

User · Answer

You can t  One workaround might be to generate a derived class at runtime and adding the attribute  although this is probably bit of an overkill

User · Answer

If you need something to be able to added dynamically  c  attributes aren t the way  Look into storing the data in xml  I recently did a project that i started w  attributes  but eventually moved to serialization w  xml

User · Answer

This really depends on what exactly you re trying to accomplish   The System ComponentModel TypeDescriptor stuff can be used to add attributes to types  properties and object instances  and it has the limitation that you have to use it to retrieve those properties as well   If you re writing the code that consumes those attributes  and you can live within those limitations  then I d definitely suggest it   As far as I know  the PropertyGrid control and the visual studio design surface are the only things in the BCL that consume the TypeDescriptor stuff   In fact  that s how they do about half the things they really need to do

[c#] Can attributes be added dynamically in C#?

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