labmda expression in select index change

private void ComboxwithLambad_Load(object sender, EventArgs e)
      {

          LoadCountries();
      }

      public class Country
      {
          public int CountryId { get; set; }
          public string CountryName { get; set; }
      }

      public class Cities
      {
          public int CityId { get; set; }
          public string CityName { get; set; }
          public int CountryId { get; set; }
      }


      private List<cities> GetAllCities()
      {
          List<cities> lstCities = new List<cities>()
          {
              new Cities(){ CityId=1, CityName="Banglore", CountryId=1},
              new Cities(){ CityId=2, CityName="Islambad",CountryId=2},
              new Cities(){ CityId=3, CityName ="Newyork",CountryId=3},
              new Cities(){ CityId=4, CityName="Chennai",CountryId=1},
              new Cities(){ CityId=5, CityName="New Delhi", CountryId=1},

              new Cities(){ CityId=6, CityName ="Peru",CountryId=2},
              new Cities(){ CityId=7, CityName="Washington D.C.",CountryId=3},
              new Cities(){ CityId=8, CityName="Trivandrum", CountryId=1},
              new Cities(){ CityId=9, CityName="Peshawar", CountryId=2},
                new Cities(){ CityId=9, CityName="Kohat", CountryId=2}

          };

          return lstCities;
      }
      private void LoadCountries()
      {
          List<country> lstCountry = new List<country>()
          {
             new Country{ CountryId =1, CountryName="India"},
             new Country{ CountryId =2, CountryName="Pakisthan"},
             new Country{ CountryId =3, CountryName="USA"}
           };

          cbCountry.DataSource = lstCountry.ToList();
          cbCountry.DisplayMember = "CountryName";
          cbCountry.ValueMember = "CountryId";


      }

      private void cbCountry_SelectedIndexChanged(object sender, EventArgs e)
      {
      }

      private void cbCountry_SelectionChangeCommitted(object sender, EventArgs e)
      {



          List<cities> allCities = new List<cities>();
          allCities = GetAllCities();

          if (cbCountry.Items.Count > 0)
          {
var citiesByCountry = allCities.Where(r => r.CountryId ==Convert.ToInt32(cbCountry.SelectedValue)).ToList();

              cbCities.DataSource = citiesByCountry;
              cbCities.DisplayMember = "CityName";
              cbCities.ValueMember = "CityId";
          }
      }