Search on the basis of dropdown values

Hi,
I have a dropdown in which I have two options, a. Selected b. Not Selected.
I want whenever the user selects any option, the search should filter on that basis. I have a column of Selection in gridview which has both option Selected and Not Selected. The values are coming from the table.
Please see the  HTML of dropdown and button for your reference:
<div style="float: left;"> <asp:DropDownList ID="ddlSort" runat="server" AutoPostBack="false" OnSelectedIndexChanged="ddlSort_SelectedIndexChanged"> <asp:ListItem Text="--Select--" Value="1"></asp:ListItem> <asp:ListItem Text="Selected" Value="2"></asp:ListItem> <asp:ListItem Text="Not Selected" Value="3& ...