check box do not response

Hi all , I get a trouble now about deleting multiple row in gridview by one check click . Here is my code.
 CheckBox chk = new CheckBox();  foreach (GridViewRow gvr in gvBatchComplete.Rows) {        chk = (CheckBox)gvr.FindControl("chkSelect");        if (chk.Checked)  { do something }
}
Here , my code for checking whether check box is checked or not  is not working .
Help me as soon as possible :(