How to load cascading dropdown in page load event?

See more:

C#

ASP.NET

I am totally confused...which are first fired in aspx page code behind events or html controls?..i have an user control in that i used cascading drop down for states,districts and areas...how to load cascading drop down in user control page load....cascading Drop down code is

<tr>
    <td class="caption">
        State:
        <asp:DropDownList ID="ddlCState" runat="server" CssClass="userentry">
        </asp:DropDownList>
        <cc1:CascadingDropDown ID="cdlCStates" TargetControlID="ddlCState" PromptText="Select State"
            ServicePath="~/CasCadingDropDown.asmx" ServiceMethod="GetStates"  runat="server"
            Category="StateId" LoadingText="Loading..." />
    </td>
</tr>
<tr>
    <td class="caption">
        District:
        <asp:DropDownList ID="ddlCDistrict" runat="server" CssClass="userentry">
        </asp:DropDownList>
        <cc1:CascadingDropDown ID="cdlCDistrict" TargetControlID="ddlCDistrict" PromptText="Select District"
            ServicePath="~/CasCadingDropDown.asmx" ServiceMethod="GetDistricts"  runat="server"
            Category="DistrictId" ParentControlID="ddlCState" LoadingText="Loading..." />
    </td>
</tr>
<tr>
    <td class="caption">
        Area:
        <asp:DropDownList ID="ddlCArea" runat="server" CssClass="userentry">
        </asp:DropDownList>
        <cc1:CascadingDropDown ID="cdlCAreas" TargetControlID="ddlCArea" PromptText="Select Area"
            ServicePath="~/CasCadingDropDown.asmx" ServiceMethod="GetAreas"  runat="server"
            Category="AreaId" ParentControlID="ddlCDistrict" LoadingText="Loading..." />
    </td>
</tr>

Web Service code is

[WebMethod]
[System.Web.Script.Services.ScriptMethod]
public CascadingDropDownNameValue[] GetStates(string knownCategoryValues)
{
    string query = "SELECT statename, stateid FROM tblstates";
    List<cascadingdropdownnamevalue> states = GetData(query);
    return states.ToArray();
}

[WebMethod]
[System.Web.Script.Services.ScriptMethod]
public CascadingDropDownNameValue[] GetDistricts(string knownCategoryValues)
{
    int state = Formats.ConvertToInt(CascadingDropDown.ParseKnownCategoryValuesString(knownCategoryValues)["StateId"]);
    string query = string.Format("select districtname,districtid from tbldistricts where stateid={0}", state);
    List<cascadingdropdownnamevalue> districts = GetData(query);
    return districts.ToArray();
}
[WebMethod]
[System.Web.Script.Services.ScriptMethod]
public CascadingDropDownNameValue[] GetAreas(string knownCategoryValues)
{
    int district = Formats.ConvertToInt(CascadingDropDown.ParseKnownCategoryValuesString(knownCategoryValues)["DistrictId"]);
    string query = string.Format("select areaname,areaid from tblareamst where district={0}", district);
    List<cascadingdropdownnamevalue> areas = GetData(query);
    return areas.ToArray();
}
[WebMethod]
[System.Web.Script.Services.ScriptMethod]
public CascadingDropDownNameValue[] GetPincode(string knownCategoryValues)
{
    int area = Formats.ConvertToInt(CascadingDropDown.ParseKnownCategoryValuesString(knownCategoryValues)["AreaId"]);
    string query = string.Format("select pincode from tblareamst where areaid={0}", area);
    List<cascadingdropdownnamevalue> Pincode = GetData(query);
    return Pincode.ToArray();
}
private List<cascadingdropdownnamevalue> GetData(string query)
{

    string connstring = String.Format("Server=192.168.1.100;Port=5432;Encoding=UNICODE;User Id=postgres;Password=sggkishore;Database=SNCF;");
    NpgsqlCommand cmd = new NpgsqlCommand(query);
    List<cascadingdropdownnamevalue> values = new List<cascadingdropdownnamevalue>();
    using (NpgsqlConnection conn = new NpgsqlConnection(connstring))
    {
        conn.Open();
        cmd.Connection = conn;
        using (NpgsqlDataReader reader = cmd.ExecuteReader())
        {
            while (reader.Read())
            {
                values.Add(new CascadingDropDownNameValue
                {
                    name = reader[0].ToString(),
                    value = reader[1].ToString()
                });
            }
            reader.Close();
            conn.Close();
            return values;
        }
    }
}