Problem loading saved data back into dropdownlist

I'm completely new to ASP.NET and Ajax, having quickly inherited a project from a consultant who is no longer with us.

Have a form with C# codebehind, and all this is running inside some Ajax components (tabcontainer and update panels). One dropdownlist (SystemID) determines the filtered values in a second dropdownlist (TypeID). In the page, there's the following to determine the source for each list:

<asp:SqlDataSourceID="sqlSystem"runat="server"

SelectCommand="Select Distinct '0' As SystemID, '(Select)' As Description From CMSSystem UNION

Select SystemID,Description From CMSSystem Where Active='1'">

</asp:SqlDataSource>

<asp:SqlDataSourceID="sqlType"runat="server"

SelectCommand="Select Distinct '0' As TypeID, '(Select)' As Description From CMSType UNION

Select TypeID, Description from CMSType Where SystemID = @dotnet.itags.org.SystemID">

<SelectParameters>

<asp:ControlParameterControlID="cboSystem"Name="SystemID"PropertyName="SelectedValue"/>

</SelectParameters>

</asp:SqlDataSource>

When I complete an empty form, the linking between the lists is fine. Select a value from SystemID, then I can select a value from TypeID that has been filtered.

The problem is on trying to load existing data. I have a procedure call inside Page_Load that loads existing values onto the form. Text boxes and checkboxes are just fine, and standalone dropdownlists are fine. I can load SystemID from a dataset row, but when I try to do the same for TypeID (trying to lookup the saved value in the list of filtered items), I find that the items collection is completely empty - and therefore, I get a null selectedvalue. What I'm guessing is that the SqlDataSource isn't "firing" (?) for the TypeID for some reason at the time of Page_Load, so I have no data to bind to the control.

Is that a good assumption, and if so, how can I get around this? I've been floundering around for a couple of weeks with this, and need any assistance I can get.

How about using the Page's Prerender event for that, instead of Load? Alternatively, you could handle theSqlDataSource's Selected event.

Didn't see any change with Page_PreRender instead of Page_Load.

I have this hunch that the SqlDataSource isn't being re-evaluated when I manually set the first dropdownlist's SelectedIndex (based on the previously saved, now retrieved, data). It must be a matter of timing or something. Trying to execute this codebehind:

if (dsRequestDetails.Tables[0].Rows[0]["SystemID"].ToString() !="")

{

liFind = cboSystem.Items.FindByValue(dsRequestDetails.Tables[0].Rows[0]["SystemID"].ToString());

cboSystem.SelectedIndex = cboSystem.Items.IndexOf(liFind);

}

if (dsRequestDetails.Tables[0].Rows[0]["TypeID"].ToString() !="")

{

liFind = cboType.Items.FindByValue(dsRequestDetails.Tables[0].Rows[0]["TypeID"].ToString());

cboType.SelectedIndex = cboType.Items.IndexOf(liFind);

}

populate the second dropdown at the ondatabound event of the first drop down. This will solve your problem