Question

Dropdownlist read its values from database and show them. I want when page loaded dropdownlist showing nothing (i.e selectedindex = -1) and user select values. any idea?

Answer 1

You can add an empty data listitem from your backend or directly from the drop down list:

From the db side:

SELECT
  1 as SortOrder,
  DataValueField,
  DataTextField
FROM
  YourTable
UNION ALL
SELECT
  0 As SortOrder,       --this ensures the empty item is at the top of the list
  0 As DataValueField,
  '' As DataTextField --or 'Select One'
Order By
  SortOrder,
  Value

Or directly in as a list item

<asp:ListItem Selected="True" Text="Select One" Value="0" AppendDataBoundItems="true" />