Cascading Dropdown List - Selecting a value in the dropdown list from a user selection


First post so hello and need some help with an issue I have been dealing with.  I have an intranet page I created in ASP.NET using C# .NET 3.5 with a few Ajax Extenders including 3 Cascading Dropdown Lists.

Now I have used the Cascading dropdown lists for my own purposes i.e they do not actually cascade their results to another dropdown list, the reason I did this was due to the having a User Control that contains an update panel and other bits i.e I didn't want the control/page posting page (something that happens when you click on a regular dropdown list).

Everything is working okay so far, I have a Web Service that takes in a context key, based on this context key then goes off to the data access layer and pulls back whatever results I asked it to, all fine so far.  The dropdown list populates with the relevant values and I am able to select a particluar item from the dropdown list without any postback issues etc, I am also able to grab the selected value when doing a postback or where I have some javascript/ajax function that is trying to workout if the user has selected something.

This particular user control also gets populated (has several fields) when a querystring is passed to the page it populates the fields during the page load (so my Page_Load method checks for this and goes off and grabs some values from a bunch of public properties to populate the user control controls).

The problem I am having is not being able to change the dropdown list that is wrapped in the extender, it's obviously grabbing the dropdown list values correctly from the web service however it completely ignores any value I try to set it to so always shows selectedindex 0 (in this case the dropdown list shows "Please Select an Item").  I've tried a few things but I just don't understand the cascading dropdown extender well enough to know whats going and how to fix this.

What I want to be able to do is to check the querystring, find a value so go off and grab the values and populate the various controls (I have a class that encapsulates the data, on a previous page the public properties of this class get populated savinging having to hit the database/dataset all over again and also allows me to keep the selected/searched record data static for that session).  During this process I want to be able to check what dropdown list value was set in the public property and then tell the dropdown list to show this value... while using the cascading dropdown extender.

If you understand the above I'll buy you a pint ;-)

Here is my web service code:

/// <summary>

/// Helper web service to populate webform Dropdown Lists

/// </summary>

[WebService(Namespace = "")] [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]


public class DropdownListBuilder : System.Web.Services.WebService


#region member variables

public static DataAccess dahelper = new DataAccess();

public static ArrayList listddldata;

List<CascadingDropDownNameValue> values = new List<CascadingDropDownNameValue>();


constructorspublic DropdownListBuilder()


//Uncomment the following line if using designed components




[WebMethod]public CascadingDropDownNameValue[] GetDropDownListData(string category, string contextKey)


DataTable dtlist = new DataTable();

// check the contextKey being passed in and retrieve a list of the dropdown list values

switch (contextKey)


case "1": // TLD/Country List

dtlist = dahelper.GetTLDCountryList();

foreach (DataRow dr in dtlist.Rows)



new CascadingDropDownNameValue((string)dr["Cakes"], dr["ID"].ToString()));



case "2": // Decision

dtlist = dahelper.GetDecisionsList();

foreach (DataRow dr in dtlist.Rows)



new CascadingDropDownNameValue((string)dr["Biscuits"], dr["ID"].ToString()));


break;case "3":

dtlist = dahelper.GetReasonList();

foreach (DataRow dr in dtlist.Rows)



new CascadingDropDownNameValue((string)dr["Jaffarcakes"], dr["ID"].ToString()));




return values.ToArray();



One of the extender's as they appear on the aspx page source:

<cc1:CascadingDropDown ID="CascadingDropDown2" runat="server" TargetControlID="ddlDecisions"

Category="Cakes" PromptText="Select a Cake... or bake one dude!" ServicePath="~/DropdownListBuilder.asmx"

ServiceMethod="GetDropDownListData" ContextKey="2" LoadingText="[Loading Cakes..]">



If you need anymore info don't hesitate to ask, I am off to smoke a cig as this has been doing my head in all day.



4/9/2008 4:41:14 PM 17816 articles. 1 followers. Follow

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