2009-02-20 The value of attributes

2009-02-20 the-value-of-attributes

# Title: The value of attributes
# Author: Mikael Lundin
# Link: http://blog.mikaellundin.name/2009/02/20/the-value-of-attributes.html

Genre1.cs

[Flags]
public enum Genre
{
    Other = 0,
    AlternativeRock = 1,
    HardRock = 2,
    WorldMusic = 4,
    Indie = 8,
    PostRock = 16
}

Genre2.cs

[Flags]
public enum Genre
{  
    [Label("Other")]
    Other = 0,

    [Label("Alternative Rock")]
    AlternativeRock = 1,

    [Label("Hard rock")]
    HardRock = 2,

    [Label("World music")]
    WorldMusic = 4,

    [Label("Indie")]
    Indie = 8,

    [Label("Post-rock")]
    PostRock = 16
}

LabelAttribute.cs

public class LabelAttribute : Attribute
{
    public LabelAttribute(string text)
    {
        this.Text = text;
    }

    public string Text { get; set; }
}

LabelAttributeHelper.cs

public static class LabelAttributeHelper
{
    /// <summary>
    /// Get label of an enum field
    /// </summary>
    public static string Label<T>(this T val)
    {
        if (!typeof(T).IsEnum)
            throw new ArgumentException("T must be an Enum");

        FieldInfo field = typeof(T).GetField(val.ToString());
        LabelAttribute[] attributes = 
            (LabelAttribute[])field.GetCustomAttributes(typeof(LabelAttribute), false);

        if (attributes.Length == 0)
            throw new ArgumentOutOfRangeException("Enum value " + val.ToString() + " is missing Label attribute");

        return attributes.First().Text;
    }
}