gistfile1.txt

using System;
using System.Reflection;

[System.AttributeUsage(System.AttributeTargets.All, Inherited = false, AllowMultiple = true)]
sealed class CustomDateTimeAttribute : System.Attribute
{
    // See the attribute guidelines at 
    //  http://go.microsoft.com/fwlink/?LinkId=85236
    readonly string positionalString;

    // This is a positional argument
    public CustomDateTimeAttribute(string positionalString)
    {
        this.positionalString = positionalString;
    }

    public string PositionalString
    {
        get { return positionalString; }
    }

    // This is a named argument
    public int NamedInt { get; set; }
}



public class CardSummaryDto
{
    [CustomDateTime("dd/mm/yyyy")]
    public string cardsentdate { get; set; }
}

class Program
{
    static void Main()
    {
        var prop = typeof(CardSummaryDto).GetProperty(nameof(CardSummaryDto.cardsentdate));
        var attr = prop.GetCustomAttribute<CustomDateTimeAttribute>();
        Console.WriteLine(attr.PositionalString);
    }
}