C#: How to add an attributes to an object at run-time?

Question

As an entity class, I want to add an attributes at run-time, how should I do?

Answer 1

I would go with PostSharp, a very elegant AOP framework (or Policy Injection).

PostSharp allows you to inject custom attributes.
The blog entry refered to in the post has some code you can download to achieve your goal.

Answer 2

Use a hashtable to store your attributes.

If you want more runtime flexibility, you might try Ruby or some other interpreted language.

Answer 3

This post answered this for me:

Dynamically Creating Types at Runtime

Answer 4

Take a look at the Dynamic Language Runtime. You also might consider a dynamic language like IronRuby or IronPython.

What problam are you trying to solve?

http://en.wikipedia.org/wiki/Dynamic_Language_Runtime

Answer 5

What needs to see the attributes? If it is things like data-binding etc, TypeDescriptor should work:

TypeDescriptor.AddAttributes(type, attribs);
TypeDescriptor.AddAttributes(instance, attribs);

This only affects System.ComponentModel usage (not direct reflection), but that is often enough - for example, you can associate a TypeConverter via the above.

If by "attributes" you mean "properties", then (again, as far as data-binding is concerned) TypeDescriptor also has potential there - but it is non-trivial; you need to either implement ICustomTypeDescriptor on the object, or to write a CustomTypeDescriptor for the type - and in either case, you need to write your own PropertyDescriptor implementation (often talking to a per-instance dictionary etc). This will get used by anything that uses:

// only works if you use TypeDescriptionProvider
PropertyDescriptorCollection typeProps = TypeDescriptor.GetProperties(type);
// works via TypeDescriptionProvider or ICustomTypeDescriptor
PropertyDescriptorCollection objProps = TypeDescriptor.GetProperties(obj);

Again, this covers a wide range of data-binding and similar scenarios. For an example of this, see here - it is far from trivial, however. The example usage (from the link) adds two properties at runtime:

Bag.AddProperty<int>("TestProp", new DefaultValueAttribute(5)); 
Bag.AddProperty<string>("Name"); 

Answer 6

Edit: please clarify, are you talking about c# attributes or members on your class?

The only way you can add c# attributes is to generate a completely new class with the additional attributes, compile and load the new assembly to your existing AppDomain.