martonx

using System;
using System.Collections.Generic;
using System.Linq;

namespace ConsoleApplication2
{
    class Program
    {
        static void Main(string[] args)
        {
            var list = new List<Test>
            (
                new Test[]
                {
                    new Test { Address = "Szeged", Email = "[email protected]", Name = "Szegedi Sandor"},
                    new Test { Address = "Debrecen", Email = "[email protected]", Name = "Debreceni Jozsef"},
                    new Test { Address = "Szeged", Email = "[email protected]", Name = "Szegedi Sandor"}
                }
            );

            var szegediek = list.WhereContainsByField("Email", "szeg");

            foreach (var item in szegediek)
            {
                Console.WriteLine(item.Email);
            }

            Console.ReadLine();

        }
    }

    public class Test
    {
        public string Name { get; set; }
        public string Address { get; set; }
        public string Email { get; set; }
    }

    public static class ExtensionMethods
    {
        public static IEnumerable<T> WhereContainsByField<T>(this IEnumerable<T> collection, string propertyName, string textToFind)
        {
            Type type = typeof(T);
            try
            {
                if (type.GetProperty(propertyName) != null)
                {
                    var collectionToReturn = new List<T>();

                    foreach (var item in collection)
                    {
                        var currentValue = type.GetProperty(propertyName).GetValue(item, null);
                        if (currentValue.ToString().Contains(textToFind))
                        {
                            collectionToReturn.Add(item);
                        }
                    }

                    return collectionToReturn;
                }
                else
                {
                    return Enumerable.Empty<T>();
                }
            }
            catch (Exception e)
            {
                // todo
                Console.WriteLine(e.Message);
                return null;
            }
        }
    }
}