为什么我的代码不会在foreach中循环

Question

我想使用复选框更新我的数据库。但似乎代码不会在foreach中循环。我哪里做错了 ？我的foreach是否有任何问题？

<?php
  foreach($_POST['listMenu'] as $checkBox1){
    $strUpdateData = "
      update tblMenuAkses
      set MenuAkses = 'N'
      where MenuAksesID = $checkBox1
    ";

    $rsUpdateData = odbc_exec($dbconnVOT,$strUpdateData);

    if($rsUpdateData){
      echo "Success";
    } else {    
      echo "ERROR <br>";
      echo odbc_errormsg($dbconnVOT);
    }
  }
  //It loops here
  var_dump($_POST['listMenu']);
?>

<form method="post" action="skrinMenu.php" enctype="multipart/form-data">
  <table align= "center" border="1" cellspacing="0" cellpadding="2">
  <?php
    $strgettable="select * from tblMenuAkses";

    $varRecCount=0;
    $rs=odbc_exec($dbconnVOT, $strgettable);
    if($rs){
      while (odbc_fetch_row($rs)) {// loop a table from database and checkbox too
        $varRecCount++; 
        echo '<tr><td>';
        echo '<center> &nbsp;'.$varRecCount.'</center>';
        echo '</td>';
        echo '<td>';
        echo '<center> &nbsp;'.odbc_result($rs,"UsrGrpNama").'</center>';
        echo '</td>';
        echo '<td>';
        echo '<center> &nbsp;'.odbc_result($rs,"MenuNama").'</center>';
        echo '</td>';
        echo '<td>';
        echo '<center> &nbsp;'.odbc_result($rs,"MenuAkses").'</center>';
        echo '</td>';
        echo '<td>';
        echo '<center> &nbsp; <input type="checkbox" name="listMenu[]" id="listMenu" value='.odbc_result($rs,"MenuAksesID").'> </center>';
        echo '</td>';
        echo '</td></tr>';          
      }
    }
  ?>            
   </table>
   <input type="submit" name="btnMenu" id="btnMenu" value = "Kemaskini">
</form>

var_dump($_POST['listMenu'])的结果：NULL