Setting DropDownList SelectedValue


David C

I have an ASP.Net page that has a FormView with multiple controls. One of
those controls is a DropDownList that is bound to a SQL table which is the
DataSource. I added an option to the DropDownList to choose <<Add>> with a
value of -1. I have a VB class function that inserts a new record and
returns the identity. This works but when I try to set the SelectedValue to
this new identity I get "'ddlAgentID' has a SelectedValue which is invalid
because it does not exist in the list of items."

The code to do this is in the Page_Load sub as follows:

varControl = row.FindControl("ddlAgentID")
If varControl.SelectedValue = -1 Then
'Run class function to create new record in tlkpAgent and return
lngNewID = DBClass.CreateNewtlkpAgent(txtNewText.Text)
'bind formview
'set dropdownlist selectedvalue to new agentid
varControl.SelectedValue = lngNewID
'txtNewText.Text = lngNewID.ToString
txtNewText.Text = ""
End If

The new record is getting created but the setting of SelectedValue is giving
error. Can anyone help? Thanks.


Scott Roberts

The error message is pretty clear, "lngNewID" does not exist in the list of
items. You need to re-populate the DropDownList after adding the new record
so that the new record is present in the ddl items list.


David C

I thought the DataBind() on the FormView would do that. What am I missing?


Scott Roberts

How is the DDL populated initially? Is it data-bound or populated manually?
If it's databound, call DataBind() on the DDL. Otherwise, re-populate
manually (or just add the new record to the Items list).

David C

I tried doing DataBind on varControl and I also tried DataBind on
SqlDataSource. Both still give me this error. Any other ideas? Do I need
to do this somewhere other than Page_Load? I'm stumped. Thanks.


Scott Roberts

I'll be honest with you, I don't use SqlDataSource or data-bound controls.
Primarily because I don't like dealing with stuff like this.

That said, it sounds like you simply need to refresh the SqlDataSource (not
sure exactly how to go about that, but I would think it should be pretty
straight-forward) so that the newly added row is included, then call
DataBind() on varControl to re-populate it.

David C

Every time I call DataBind() on varControl I get "Databinding methods such
as Eval(), XPath(), and Bind() can only be used in the context of a
databound control."

This really sucks. There has to be a solution to this because it is so easy
in other languages.

Scott Roberts

So the control is not data-bound after all? You've really not given us much
to work with.

How is the DDL populated? What does the control look like in the aspx? If
you are doing the data-binding in the code-behind, what does that code look

I'm envisioning something like this:

myDataSource.Refresh(); // pick up the new record. not sure of the
varControl.DataSource = myDataSource; // the datasource is not persisted in
the viewstate. it must be declared in the aspx or re-assigned on each
varControl.DataBind(); // populate the control.

David C

Below is the DDL control and below it is the DataSource. Hope this helps.


<asp:DropDownList ID="ddlAgentID" runat="server" DataSourceID="SqltlkpAgent"
DataTextField="Agent" DataValueField="AgentID" SelectedValue='<%#
Bind("AgentID") %>' Width="300" AppendDataBoundItems="true">
<asp:ListItem Value="-1" Text="&lt;&lt;New Agent&gt;&gt;"></asp:ListItem>

<asp:SqlDataSource ID="SqltlkpAgent" runat="server" ConnectionString="<%$
ConnectionStrings:FiledataConnectionString %>"
SelectCommand="SELECT 0 As AgentID, NULL As Agent UNION SELECT [AgentID],
[Agent] FROM [tlkpAgent] ORDER BY [Agent]">

Scott Roberts


All you need is "varControl.DataBind()" right after you create a new record.

If you look closely at your dropdownlist control after inserting a new
record, I think you'll find that all of your Agents are in the list TWICE.
The new agent is in there, but it's in the 2nd copy of agents (toward the
bottom of the list).

Why is that? You have AppendDataBoundItems="true" which appends items to the
list instead of refreshing the list. Set AppendDataBoundItems="false" and
you'll get what you want.



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