Ajax Cascading Dropdownlist parent cotrol id is working only if i selected but using selected value i m not getting

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C#

webservice

Ajax Cascading Dropdownlist parent cotrol id is working only if i selected but using selected value(for example from textbox value the dropdown is bind then child drop down control is not active) i m not getting
I m using web method

[WebMethod]
public CascadingDropDownNameValue[] get_Districts(string knownCategoryValues, string category)
{
    DataTable dtMainModule = new DataTable();
    string StateID;

    StringDictionary MainModuleValues = 
           AjaxControlToolkit.CascadingDropDown
                     .ParseKnownCategoryValuesString(knownCategoryValues);

    StateID = "09";// MainModuleValues["StateID"];
    dtMainModule = 
        odal.ReturnDt(@"select distinct DistrictID,DistrictName from  bindPS.tblVillage where StateID='" + StateID + "'");
    List<cascadingdropdownnamevalue> objMainModule = new List<cascadingdropdownnamevalue>();

    foreach (DataRow dr in dtMainModule.Rows)
    {
         objMainModule.Add(new CascadingDropDownNameValue
               (Convert.ToString(dr["DistrictName"]), 
                Convert.ToString(dr["DistrictID"])));
     }
     
     return objMainModule.ToArray();
}
</cascadingdropdownnamevalue></cascadingdropdownnamevalue>