Custom attribute on property - Getting type and value of attributed property

Solution 1:

Something like the following,, this will use only the first property it comes accross that has the attribute, of course you could place it on more than one..

    public object GetIDForPassedInObject(T obj)
    {
        var prop = typeof(T).GetProperties(BindingFlags.Public | BindingFlags.Instance)
                   .FirstOrDefault(p => p.GetCustomAttributes(typeof(IdentifierAttribute), false).Count() ==1);
        object ret = prop !=null ?  prop.GetValue(obj, null) : null;

        return ret;
    }  

Solution 2:

public class TestClass<T>
{
    public void GetIDForPassedInObject(T obj)
    {
        PropertyInfo[] properties =
            obj.GetType().GetProperties(BindingFlags.Public | BindingFlags.Instance);            

        PropertyInfo IdProperty = (from PropertyInfo property in properties
                           where property.GetCustomAttributes(typeof(Identifier), true).Length > 0
                           select property).First();

         if(null == IdProperty)
             throw new ArgumentException("obj does not have Identifier.");

         Object propValue = IdProperty.GetValue(entity, null)
    }
}

Solution 3:

A bit late but here is something I did for enums (could be any object also) and getting the description attribute value using an extension (this could be a generic for any attribute):

public enum TransactionTypeEnum
{
    [Description("Text here!")]
    DROP = 1,

    [Description("More text here!")]
    PICKUP = 2,

    ...
}

Getting the value:

var code = TransactionTypeEnum.DROP.ToCode();

Extension supporting all my enums:

public static string ToCode(this TransactionTypeEnum val)
{
    return GetCode(val);
}

public static string ToCode(this DockStatusEnum val)
{
    return GetCode(val);
}

public static string ToCode(this TrailerStatusEnum val)
{
    return GetCode(val);
}

public static string ToCode(this DockTrailerStatusEnum val)
{
    return GetCode(val);
}

public static string ToCode(this EncodingType val)
{
    return GetCode(val);
}

private static string GetCode(object val)
{
    var attributes = (DescriptionAttribute[])val.GetType().GetField(val.ToString()).GetCustomAttributes(typeof(DescriptionAttribute), false);

    return attributes.Length > 0 ? attributes[0].Description : string.Empty;
}