Update Panel and Drop Down List databinding twice - lifecycle

Question

I think this is an asp.net page life cycle question, but none the less, i can't quite figure it out.

I have a drop down list in an update panel that lists users and then shows details below it (update or delete). When the I click delete, the code behind goes and clears the ddl (to remove the deleted user), and then rebinds it. All fine. Somewhere between the end of the code behind and when the page updates, it then appends the list again.

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        DropDownList1.AppendDataBoundItems = true;
        DropDownList1.Items.Insert(0, new ListItem("Select a User", "select"));
        DropDownList1.SelectedValue = "select";
        DropDownList1.DataSourceID = "srcUsers";
        DropDownList1.DataBind();
    }
}
protected void btnDelete_Click(object sender, EventArgs e)
{
    DropDownList1.AppendDataBoundItems = false;
    DropDownList1.DataSourceID = "srcUsers";
    DropDownList1.DataBind();
    DropDownList1.AppendDataBoundItems = true;
    DropDownList1.Items.Insert(0, new ListItem("Select a User", "select"));
    DropDownList1.SelectedValue = "select";
}//at this point, the quick watch shows the correct count for the ddl

<asp:UpdatePanel ID="UpdatePanel1" runat="server">
  <ContentTemplate>
     <asp:DropDownList ID="DropDownList1"  Width="150"  runat="server" OnSelectedIndexChanged="DropDownList1_SelectedIndexChanged" AutoPostBack="true">
     </asp:DropDownList>
  </ContentTemplate>
  <Triggers>
     <asp:AsyncPostBackTrigger ControlID="DropDownList1" EventName="SelectedIndexChanged" />
  </Triggers>
</asp:UpdatePanel>

Note: srcUsers is a object data source

If I remove the ddl binding code from the button, then it doesn't update the ddl at all (with it in, it does it twice!)

Where is it binding the second time? Why isn't it binding if I remove the button code? How come I can't step through this in VS?

Answer 1

Check the code below if it can help you.

 protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            BindCombo();

        }
    }
    public void BindCombo()
    {
        DropDownList1.Items.Clear();
        DropDownList1.AppendDataBoundItems = true;
        DropDownList1.Items.Insert(0, new ListItem("Select a Category", "select"));
        DropDownList1.SelectedValue = "select";
        DropDownList1.DataSourceID = "ds1";
        DropDownList1.DataBind();

    }

   protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
    {
        //---- It can be placed in delete button's click event also ------//
        ds1.DeleteCommand = "Delete from Categories where CategoryID="+DropDownList1.SelectedValue;
        ds1.Delete();
        BindCombo();
        //---- It can be placed in delete button's click event also ------//
    }

Answer 2

Himadri's code got me thinking (thanks for the effort!!!!) that for delete operations, i really didn't need to rebind the dropdownlist, i have the SelectedValue.... so i can just delete it from the dropdownlist.

DropDownList1.Items.Remove(selectedValue);

Duh.

I have on the other half of the page code that does an insert type operation (hence the update panel) that was calling the same code (Himadri's BindCombo) and having the same issue, but i think i can find a similar solution.

I still would like to know how the VS debugger lets that happen.

Thanks again Himadri!