Question

We have a custom attribute

[AttributeUsage(AttributeTargets.All, AllowMultiple = true)]
public class CustomDesignerAttribute: Attribute

then we have a base class decorated with this attribute

[CustomDesigner(someKey, someValue)]
public class BaseClass

then we have a class derived from this one, decorated with same attribute (with same key, different value)

[CustomDesigner(someKey, someOtherValue)]
public class ChildClass : BaseClass

Is there possibility that ChildClass don’t create a duplicate of attribute but overwrite a value for existing key instead (overwrites whole parent attribute)?
If not, what’s the best pattern for getting default value from BaseClass if ChildClass has not defined his own?

Answer 1

No, it’s not possible to override the existing attribute.

Attributes are metadata attached to an object (assembly, class, method, variable and so on) so they always keep this connection.

If you want to give a default “behavior” in the base class and override it in some derived classes you have to check all the attributes returned by GetCustomAttributes() to use only the most derived one (the first in the list).