CustomAttribute中的C＃CodeDOM枚举值

Question

I am trying to create a class with a custom attribute that looks like:

public class Head : Attribute 
{
    public Head(Permissions permission, int id)
    {
        Permission = permission;
        Id = id;
    }

    public int Id { get; private set; }
    public Permissions Permission { get; private set; }
}

where Permissions is an enum:

public enum Permissions { R, W, D, RW, RWD }

so when I generate the attribute:

var head = new CodeAttributeDeclaration
{
    Name = "Head",
    Arguments = 
    {
        new CodeAttributeArgument
        {
            Value = new CodePrimitiveExpression(Permissions.RWD)
        },
        new CodeAttributeArgument
        {
            Value = new CodePrimitiveExpression(idValue);
        }
    }
}

When I try to generate this I get ArgumentException and a hint of using CodeObjectCreateExpression, but since Attributes can only take constant values I wonder how this could be achieved?

Answer 1

Try to write the code you want to generate:

[Head(Permissions.RWD, 42)]

If you do that, you'll realize there is no "primitive expression" for enums, you need to write it as if you were accessing a static field:

new CodeFieldReferenceExpression(
    new CodeTypeReferenceExpression(typeof(Permissions)), "RWD")