Chech/uncheck checkboxlist and 1st time I "select all" it select all all items then if i try to select other then "select all" then "select all" should be unchecked

Dim i As String = checkbox1.SelectedValue
Dim index As Integer = 0

    If i <> "" Then
          index = Convert.ToInt16(CheckBoxList1.SelectedValue)
       End If

 if index = 1 Then

' index of select all checkbox '

   checkbox1.Items(2).checked = False
   checkbox1.Items(3).checked = False
   checkbox1.Items(4).checked = False

Else

   checkbox1.Items(2).checked = True
   checkbox1.Items(3).checked = True
   checkbox1.Items(4).checked = True

End If
End Sub

This what you mean???

You can check this jquery implementation

<script type="text/javascript">

        $(document).ready(function () {
            $("input[id*='CheckBoxList1']").click(function (e) {
                var currentId = $(this);
                if (currentId.val() == "select all") {
                    $("input[id*='CheckBoxList1']").each(function () {
                        if ($(this).val() != "select all")
                            $(this).attr("checked", true);
                    });
                }
                else {
                    $("input[id*='CheckBoxList1'][value*='select all']").attr("checked", false);
                }              
            });

        });
    
    
    </script>

<div>
        <asp:checkboxlist id="CheckBoxList1" runat="server" xmlns:asp="#unknown">
            <asp:listitem>select all</asp:listitem>
            <asp:listitem>a</asp:listitem>
            <asp:listitem>b</asp:listitem>
            <asp:listitem>c</asp:listitem>
            <asp:listitem>d</asp:listitem>
        </asp:checkboxlist>
    </div>

i have solved this from 1 link which i dont remember... but it helped me to solve my solution and i thank for that link....

using javascript for asp controls...

<script type="text/javascript">
function all()
{
if(document.getElementByid('chkall').checked==true)
{
document.getElementByid(chkA).checked=true;
document.getElementByid(chkB).checked=true;

}
else
{
document.getElementByid(chkA).checked=false;
document.getElementByid(chkB).checked=false;
}
}

function forA()
{
if(document.getElementByid('chkA').checked==false)
{
document.getElementByid('chkall').checked=false;
}
}

---same for checkbox B----

</script>

at your source for checkbox id=checkboxall write onclick="all()"---this will call function

and for id=checkboxA write onclick="forA()"

and so on