How to set a asp:DropDownList SelectedValue to a Session Variable?

Question

There are several articles describing how to do this is code behind however:

Is it possible to set the value of a dropdownlist to a session variable on the aspx page?

I am using SqlDataSource to populate the dropdownlist so do not wish to add code behind if it can be avoided.

<asp:DropDownList ID="ddl" runat="Server" DataSourceID="sqlDS" DataValueField="ID" DataTextField="TEXT" AppendDataBoundItems="true">
  <asp:ListItem Text="" Value="" Selected="True" />
</asp:DropDownList>

<asp:SqlDataSource ID="sqlDS" runat="Server" SelectCommand="spDS" SelectCommandType="StoredProcedure" />

Set Session("ID") as selected value on load?

---

The dropdown list is already populated from the sqldatasource. I just want to set the initial value on page load.

Answer 1

You need a server side code in order to use Session. The following code doesn't requires code behind file, but again the code inside script will run at server side.

<asp:DropDownList ID="ddl" runat="Server" 
   DataSourceID="sqlDS" 
   DataValueField="ID" 
   DataTextField="TEXT" 
   AppendDataBoundItems="true"
   OnSelectedIndexChanged="ddl_SelectedIndexChanged" 
   AutoPostBack="True">
  <asp:ListItem Text="" Value="" Selected="True" />
</asp:DropDownList>

<asp:SqlDataSource ID="sqlDS" runat="Server" 
  SelectCommand="spDS" SelectCommandType="StoredProcedure" />

<script runat="server">
    protected void ddl_SelectedIndexChanged(object sender, EventArgs e)
    {
        Session["SelecteValue"] = ddl.SelectedValue;
    }
</script>

Note: Make sure AutoPostBack="True" for DropDownList.

Answer 2

Do not mix code with markup. It makes sense to separate them for many reasons. So ASPX will have just the presentation, and CS/VB just the code logic.

When you compile/deploy your side to production - there will not be "the second page" - only ASPX page will remain. Code will be compiled into a DLL.

Answer 3

you'll need an event for your dropdown list on change. Are you using C# or VB.net for your codebehind?

add to onSelectedIndexChanged="ddl_OnSelectedIndexChanged"

to your code behind add:

{this is C# vb is similar}

protected void ddl_OnSelectedIndexChanged(Object sender, EventArgs e)
{
    Session["selectedID"] = ddl.selectedValue;
}

to your page load, add

if (isPostback)
{
    ddl.selectedValue = Session["selectedID"];
}