ListView.selectedIndex always returns value -1 in vb.net

<asp:ListView ID="lvSectors" runat="server" DataKeyNames="SectorID" OnItemCommand="lvSelectors_ItemCommand"
OnSelectedIndexChanged="lvSelectors_SelectedIndexChanged" OnSelectedIndexChanging="lvSelectors_SelectedIndexChanging">
<layouttemplate>
<table id="itemPlaceholderContainer" runat="server" align="center" border="1" cellpadding="0"
cellspacing="0">
<tr runat="server" style="">
<th align="center">
<asp:LinkButton ID="lbSr_No" runat="server" CommandName="Sort" Width="150"><span style="color :Blue ">Sr No</span>
</th>
<th align="center">
<asp:LinkButton ID="lbSector_Text" runat="server" CommandName="Sort" Width="150"><span style="color :Blue ">SectorName</span>
</th>
<th align="center">
<asp:LinkButton ID="lbDescription" runat="server" CommandName="Sort" Width="150"><span style="color :Blue ">Description</span>
</th>
<th>
Edit
</th>
<th>
Delete
</th>
</tr>
<tr id="itemPlaceholder" runat="server">
</tr>
</table>
<asp:DataPager ID="dpSectors" runat="server" PagedControlID="lvSectors">


<itemtemplate>
<tr>
<td align="center">
<%#Container.DataItemIndex+1 %>
</td>
<td align="center">
<asp:Label ID="lblSector_Text" runat="server" Text='<%#Bind("SectorText") %>'>

</td>
<td align="center">
<asp:Label ID="lblDescription" runat="server" Text='<%#Bind("Description") %>'>

</td>
<td align="center" id="edit1">
<asp:LinkButton ID="lbSector_Edit" runat="server" Width="150" CommandArgument='<%#Bind("SectorID") %>'
CommandName="Select" Text="Edit" CssClass="editclass">
</td>
<td align="center">
<asp:LinkButton ID="lbSector_Delete" runat="server" CommandArgument='<%#Bind("SectorID") %>'
CommandName="Remove" Width="150" Text="Delete" CssClass="deleteClass" OnClientClick='return confirm("Are you sure you want to delete this entry?");'>
</td>
</t