set selected value based off parent value - asp.net

Question

I have 2 cascading drop downs, 1 is a parent and the other/child populates once you select a value in the first/parent drop down.
The first one populates on page load and I can set the selected value for this one based off database value that was saved on previous page.
For the second cascading drop down it populates for me when I set the selected value for the parent ID on page load (based off the database value).
But since the second/child drop down is not set/loaded with values until the page loads I can not set the selected value (I tried on Page_Load_Complete but it does not work there either).
I need to know how once I set the selected value in the parent drop down (this works fine), to populate the second drop down based off the value in the first one.
Here is my code for the aspx page. I can set the first selected value, and it populates the second select box (but I can not set the selected value because it is not populated at the time I set the first selected value.
aspx page
<asp:Label ID="lblAffPartCat" Text="<%$ Resources:share,lblAffPartCat %>" runat="server"></asp:Label>
<asp:DropDownList ID="ddlPartCat" runat="server"></asp:DropDownList>
<ajaxToolkit:CascadingDropDown ID="CascadingDropDown2" runat="server" TargetControlID="ddlPartCat"
Category="BasePart" PromptText="<%$ Resources:share,lblSelPartCat %>" LoadingText="[Loading Part Cat...]"
ServicePath="PAIntExtPart.asmx" ServiceMethod="BindPartCat"
ContextKey="" UseContextKey="True"/>
<asp:Label ID="lblAffBasePart" Text="<%$ Resources:share,lblAffBasePart %>" runat="server"></asp:Label>
<asp:DropDownList ID="ddlBasePart" runat="server" ></asp:DropDownList>
<ajaxToolkit:CascadingDropDown ID="ddlBasePart_CascadingDropDown" runat="server" Category="BasePart"
TargetControlID="ddlBasePart" ParentControlID= "ddlPartCat" PromptText="<%$ Resources:share,lblSelBasePart %>"
LoadingText="Loading Base Parts.."
ServicePath="PAIntExtPart.asmx"
ServiceMethod="BindBasePart"
ContextKey="" UseContextKey="True" />
asmx.cs page that populates the drop downs:
using System;
using System.Collections.Generic;
using System.Web.Services;
using System.Data;
using System.Collections.Specialized;
using AjaxControlToolkit;
using Hotline.DataAccess;
/// <summary>
/// Summary description for PAIntExtPart
/// </summary>
[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
[System.ComponentModel.ToolboxItem(false)]
// To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line.
[System.Web.Script.Services.ScriptService()]
public class PAIntExtPart : System.Web.Services.WebService
{
string _SiteLocation = MiscFunctions.getCurrentSiteLocation();
/// <summary>
/// WebMethod to Populate Part Category Dropdown
/// </summary>
[WebMethod]
public CascadingDropDownNameValue[] BindPartCat(string knownCategoryValues, string category, string contextKey)
{
DataTable dsPartCat = null;
// string passed for contextKey is FormType and Language split by ":"
string[] arrcontextKey = contextKey.Split(':');
string FormType = arrcontextKey[0].ToString();
int LanguageID = Int32.Parse(arrcontextKey[1].ToString());
string PartCatValue = arrcontextKey[2].ToString();
try
{
dsPartCat = HarDB.getPartCat(_SiteLocation, LanguageID, FormType);
//create list and add items in it by looping through dataset table
List<CascadingDropDownNameValue> PartCatdetails = new List<CascadingDropDownNameValue>();
foreach (DataRow dtrow in dsPartCat.Rows)
{
string PartCatID = dtrow["PartCatID"].ToString();
string PartCat = dtrow["PartCat"].ToString();
PartCatdetails.Add(new CascadingDropDownNameValue(PartCat, PartCatID));
}
if (PartCatValue.Trim() != "")
{
//SelectedValue = PartCatValue;
}
return PartCatdetails.ToArray();
}
catch (Exception ex)
{
Server.Transfer("Errorpage.aspx?function=getAttachInfo+Error=" + Server.UrlEncode(ex.Message));
return null;
}
}
/// <summary>
/// WebMethod to Populate Base Part Dropdown
/// </summary>
[WebMethod]
public CascadingDropDownNameValue[] BindBasePart(string knownCategoryValues, string category, string contextKey)
{
string PartCatID;
//int LanguageID = Int32.Parse(contextKey);
string[] arrcontextKey = contextKey.Split(':');
string FormType = arrcontextKey[0].ToString();
int LanguageID = Int32.Parse(arrcontextKey[1].ToString());
string BasePartValue = arrcontextKey[2].ToString();
//This method will return a StringDictionary containing the name/value pairs of the currently selected values
StringDictionary PartCatdetails = AjaxControlToolkit.CascadingDropDown.ParseKnownCategoryValuesString(knownCategoryValues);
PartCatID = PartCatdetails["BasePart"];
DataTable dsBasePart = null;
try
{
dsBasePart = HarDB.getBasePart(_SiteLocation, LanguageID, PartCatID, FormType);
//create list and add items in it by looping through dataset table
List<CascadingDropDownNameValue> BasePartdetails = new List<CascadingDropDownNameValue>();
foreach (DataRow dtrow in dsBasePart.Rows)
{
string BasePartID = dtrow["BasePartNumID"].ToString();
string BasePart = dtrow["BasePartNum"].ToString();
BasePartdetails.Add(new CascadingDropDownNameValue(BasePart, BasePartID));
}
if (BasePartValue.Trim() != "")
{
//SelectedValue = PartCatValue;
}
return BasePartdetails.ToArray();
}
catch (Exception ex)
{
Server.Transfer("Errorpage.aspx?function=getAttachInfo+Error=" + Server.UrlEncode(ex.Message));
return null;
}
}
}

Answer 1

I found out my issue, I was not using the correct "Selected Value" when trying to populate the second drop down.