在ajax连接选择中提交后保持选择

Question

我用这种方式制作了一个动态/连接选择的表单。

FORM HTML（index.php）

<form id="src_form" action="index.php" method="post">
<p>
<select name="catid_1" id="catid_1" class="fieldmax">
   <?php echo $cs->show_cat_1(''); ?>
</select>
</p>
<p>
<select name="catid_2" id="catid_2" class="fieldmax">
   <option value="">&nbsp;</option>
</select>
</p>
<p>
<select name="catid_3" id="catid_3" class="fieldmax">
   <option value="">&nbsp;</option>
</select>
</p>
<p>
<input type="submit" name="submit" value="SRC" id="btn_src">
</p>
</form>

AJAX JS

$(function() {

// Ajax post Page
var urlpage = 'ajax-php/con-select.php';

// Vars 
var wait = '<option value="">wait</option>';
var all = '<option value="">all</option>';

// Default
$("select#catid_2").prop("disabled", true);
$("select#catid_3").prop("disabled", true);

// CATID_1 Change
$("select#catid_1").change(function(){

// set var
var catid_1 = $("select#catid_1 option:selected").prop("value");

// laod
$("select#catid_2").html(wait);


$.post(urlpage, 
{ 
    catid_1:catid_1 
}, 
function(data){

    switch (data) {

        case all:
            $("select#catid_2").html("");
        return false;

        default:
            $("select#catid_2").prop("disabled", false);
            $("select#catid_2").html(data);
        return false;
        }
    });
});

// CATID_2 Change ... etc

}); 

CON-SELECT.PHP

if(isset($_POST['catid_1']))
{
    echo $cs->show_cat_2();
    die;
}

if(isset($_POST['catid_2']));
{
    echo $cs->show_cat_3();
    die;
}

CLASS.PHP

public function show_cat_1() 
{
$result = $this->db->mysqli->query
("SELECT * FROM cat_1 ORDER BY idcat_1 ASC");

$cat_1 = '<option value="">all</option>';

while($row = $result->fetch_assoc()) 
{
$cat_1 .= '<option value="' . $row['idcat_1'] . '"';
$cat_1 .= '>' . $row['idcat_1'] . '</option>';
}
return $cat_1;
}

public function show_cat_2() 
{
$result = $this->db->mysqli->query
("SELECT * FROM cat_2 ORDER BY idcat_2 ASC");

$cat_2 = '<option value="">all</option>';

while($row = $result->fetch_assoc()) 
{
$cat_1 .= '<option value="' . $row['idcat_2'] . '"';
$cat_1 .= '>' . $row['idcat_2'] . '</option>';
}
return $cat_2;
}

etc..

我的目标是在提交表单（重新加载页面）后保留其选项（选择值），同时保持其功能。你能行的？我怎么能这样做？感谢