wordpress admin panel get parameter - php

Question

I'm developing a plugin in wordpress, there is data that needs to be listed by search but I can't get them with the get parameter.
I can send with the post parameter, but when the user refreshes the page, she has to search again according to the order number.
Following my code:functions.php
add_action('admin_menu', 'testPluginAdminMenu');
function testPluginAdminMenu()
{
add_menu_page('Return Request',
'Return Request',
'manage_options',
'list',
'myFunction'
);
add_submenu_page(
'null',
'Return Request List',
'Return Request List',
'manage_options',
'listAll',
'myFunctionList');
}
index.php
<?php
function myFunctionList(){
if(isset($_GET['request_order'])){
echo $search = $_GET['request_order'];
}
}
function myFunction(){ ?>
<form method="get" action="<?php echo admin_url('admin.php?page=listAll&request_order='.$_GET['request_order'] ) ?>">
<input type="text" name="request_order" placeholder="Search Order Number..">
<button type="submit" >Search</button>
</form>
<?php } ?>
Output from url: localhost/wordpress/wp-admin/admin.php?request_order=7481
page=listAll not appearing on url
Thank you advance.

Answer 1

Can you try something like this
$qs = array(
'page' => 'listAll',
'request_order' => $_GET['request_order']
);
$qs = http_build_query($qs, null, "&", PHP_QUERY_RFC3986);
<?php echo admin_url('admin.php?' . $qs ) ?>
UPDATE 1
<form method="get" action="<?php echo admin_url('admin.php?page=listAll&request_order='.$_GET['request_order'] ) ?>">
<input type="text" name="request_order" placeholder="Search Order Number..">
<input type="hidden" name="page" value="listAll" />
<button type="submit" >Search</button>
</form>