Get selected values of checkbox from GridView in ASP.NET

   Private Function SelectedValues() As String
        Dim strValues As String = ""
        For i As Integer = 0 To GridView.Rows.Count - 1
            Dim chkSelect As CheckBox
            chkSelect = CType(gvClientContact.Rows(i).FindControl("chkSelect"), CheckBox)
            If Not chkSelect Is Nothing Then
                If chkSelect.Checked Then
                    strValues &= CStr(GridView.DataKeys(i).Values(0)) & ","
                End If
            End If10/09/2010
        Next
        Return strValues.Trim(CChar(","))
    End Function

Get selected checkbox value of ASP.NET GRID VIEW using JavaScript

<script language="javascript" type="text/javascript">

        function GetSelected(objchk, HId) {
            var hdnIds = document.getElementById("<%= hdnIds.ClientId %>");

            if (hdnIds.value.length == 0) {
                hdnIds.value = ",";
            }

            if (objchk.checked == true) {
                hdnIds.value = hdnIds.value + HId + ",";

            }
            else {

                hdnIds.value = hdnIds.value.replace("," + HId + ",", ",")
            }
        }
    </script>

---

    'Bind this function like     On GridView's RowDataBound Event.
    Private Sub gv_RowDataBound(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewRowEventArgs) Handles gv.RowDataBound
        Dim chkSelect As CheckBox = CType(e.Row.FindControl("chkSelect"), CheckBox)
        If Not chkSelect Is Nothing Then
            chkSelect.Attributes.Add("onclick", "GetSelected(this,'" & DataBinder.Eval(e.Row.DataItem, "HId").ToString() & "');")
        End If
    End Sub
    'Now you have comma seperated values of HIds in hdnIds hidden field which you can use accordingly