使用 C# 中的自定义属性将标头信息添加到枚举

Question

I am able to create and build my own attributes and use them from within an enum, but I am unable to use these attributes as header information to an enum.

For instance, consider the following enum:

    [EnumSize(0x30000)]
    public enum Memories
    { 
        [MemSize(0x10000)]
        [Description("Memory0")]
        Memory0Base = 0x00000,

        [MemSize(0x10000)]
        [Description("Memory1")]
        Memory1Base= 0x10000,

        [MemSize(0x10000)]
        [Description("Memory2")]
        Memory2Base= 0x20000
    }

Now, I have created both EnumSize and MemSize attributes in the following way:

public class EnumSizeAttribute : System.Attribute
{
    private int _value;
    public EnumSizeAttribute(int value)
    {
        _value = value;
    }
    public int Value
    {
        get { return _value; }
    }
}

And made it more "access friendly" (meaning I can do something like this: Memories.Memory2Base.MemSize() or Memories.EnumSize()):

public static string EnumSize<T>(this T value)
{
    FieldInfo fi = value.GetType().GetField(value.ToString());

    EnumSizeAttribute[] attributes = (EnumSizeAttribute[])fi.GetCustomAttributes(typeof(EnumSizeAttribute), false);

    if (attributes.Length > 0)
        return attributes[0].EnumSize();
    else
        return value.ToString();
}

Now, although it generates no compilation error when using it as a header to my enum as here below, I am unable to get the EnumSize by doing "Memories.EnumSize()".

[EnumSize(0x30000)]
public enum Memories
{ 
 ...
}

Any tip on how to get it to work would be very much appreciated.

Answer 1

Memories is a type not a field, so you would need to do something like this:

public static string EnumSize<T>() where T : struct, Enum
{
    EnumSizeAttribute attribute = typeof(T).GetCustomAttribute<EnumSizeAttribute>();

    return attribute?.Value.ToString();
}

And use as follows:

string size = EnumSize<Memories>();

You won't be able to call this as an extension method like you have with MemSize though.

The only way to do that would be to extend Type , for example:

public static string EnumSize(this Type type)
{
    EnumSizeAttribute attribute = type.GetCustomAttribute<EnumSizeAttribute>();

    return attribute?.Value.ToString();
}

string size = Memories.EnumSize();

But that would be available to use with all types, not just enums, which is probably not what you want.

Of course you could throw an exception if it is used incorrectly:

public static string EnumSize(this Type type)
{
    if (!type.IsEnum)
    {
        throw new InvalidOperationException("EnumSize only applies to enums");
    }

    EnumSizeAttribute attribute = type.GetCustomAttribute<EnumSizeAttribute>();

    return attribute?.Value.ToString();
}

But I would probably stick to the first example.