Retain values in jquery - php

Question

I have 4 dropdowns namely dd1(parent),dd2,dd3,dd4 with last three dropdowns having null as a initial value.
I use ajax to fetch last three dropdowns from parent dropdown.
I have used php validation(mkValid) to validate whether the dropdowns are empty or not.
The problem is when i select a value in first 2 dropdowns and when i click on submit,it gets validated but the page gets refreshed and the selected value in first two dropdowns becomes empty.So,i need to retain those values until all dropdowns have values.I used ajax.stop() in jquery but no use.Help.!

Answer 1

You must validate the dropdowns clientside.
PHP is serverside and only validate after posting it to the server. This happens after you click "submit".
Show us your code ;)
Prevent the submit with:
$('#form_id').submit(function(e) {
e.preventDefault();
// or
//return false;
})

Answer 2

You can do it like this:
<select name="dropdown">
<option value="1" <?php echo isset($_POST["dropdown"]) && $_POST["dropdown"] == "1" ? "selected"; ?> >Option 1</option>
<option value="2" <?php echo isset($_POST["dropdown"]) && $_POST["dropdown"] == "2" ? "selected"; ?> >Option 2</option>
<option value="3" <?php echo isset($_POST["dropdown"]) && $_POST["dropdown"] == "3" ? "selected"; ?> >Option 3</option>
</select>
You can refer to PHP How can I keep the selected option from a drop down to stay selected on submit? for more information
EDIT: I just read you are using Smarty, in which case you can use:
<select name="dropdown">
<option value="1" {if !empty($dropdown) && $dropdown == "1"}selected{/if}>Option 1</option>
<option value="2" {if !empty($dropdown) && $dropdown == "2"}selected{/if}>Option 2</option>
<option value="3" {if !empty($dropdown) && $dropdown == "3"}selected{/if}>Option 3</option>
</select>
And in your PHP:
global $smarty;
if(isset($_POST["dropdown"])){
//validation
$smarty->assign("dropdown", $_POST["dropdown"]);
}