Cannot seem to use $_POST twice on the same page - php

Question

I am trying to access different elements in an XML so I can edit them or add new ones from within a web page. I'm using PHP to loop through the parent tags and display in a select list then have submit button to POST the element selected - no issue.
I then use PHP to find all the names of the selected elements children, and display those names in another select list form. This displays the children in the list correctly however when I hit submit it displays correctly if I echo $_POST("Section") but clears the previous $_POST("Page").
I think this has something to do with using action="", but interestingly if I change one them to GET it works as intended. I actually want a 3rd step into lower children again, so cannot use that solution as a dodgy workaround.
I wont post XML as it has sensitive data in it and you can just trust I am stepping through that fine, it's the php clearing $_POST that is the big issue for me.
Please go easy - I literally learnt how to make a basic html webpage in april.
Tried a bunch of different form action including the .php it is on, and also
<?php echo $_SERVER['PHP_SELF']; ?>" >
As stated before - using one as GET and one POST seems to solve the issue
<?php
//pages processing and put into an array
$pages_array = array();
$xml = simplexml_load_file('XML/links.xml') or die ("Failed to load");
foreach($xml->page as $page){
array_push($pages_array, $page->name);
}
$pagecount = count($pages_array);
?>
<form name="page_select" method="POST" action="">
<select name="Page">
<?php
for ($i = 0; $i < $pagecount; $i++){
print '<option>'.$pages_array[$i].'</option><br>';
}
?>
</select>
<input type="Submit" name="edit_page" value="edit"/>
</form>
<br></br>
<?php
// save page selected into $pg and display page being edited
$pg = $_POST["Page"];
echo 'YOU ARE EDITTING PAGE: '.$pg;
?>
****** THEN FURTHER DOWN THE PAGE *****
<?php
// section processing
$section_array = array();
$xml = simplexml_load_file('XML/links.xml') or die ("Failed to load");
foreach($xml->page as $page){
if($page->name == $pg){
foreach($page->sections->section as $section){
array_push($section_array, $section->name);
}
}
}
$sectioncount = count($section_array);
?>
<form name="section_select" method="POST" action="">
<select name="Section">
<?php
for ($i = 0; $i < $sectioncount; $i++){
print '<option>'.$section_array[$i].'</option><br>';
}
?>
</select>
<input type="Submit" name="edit_section" value="edit"/>
</form>
<br></br>
<?php
$sct = $_POST["Section"];
echo 'YOU ARE EDITTING SECTION: '.$sct;
?>
I want output to remember both arrays after the second form is submitted, however due to the first POST variable being wiped it means I also lose the second array since when it gets back to pushing to $section_array $page->name can never = $pg since $pg is now empty

Answer 1

Every time you submit a form, the page is reloaded and PHP will only have access to the POST variables from the form that triggered the page reload. This means that as your second form is submitted, $_POST['Page'] ceases to exist.
There are many ways around this problem, here is a fairly simple one. In your second form, create a hidden input that contains the value of the $_POST['Page'] variable. That way, when the second form is submitted, the Page value will be propagated to the next step of the process. Adding this code to your section_select form should suffice:
<?php
if(isset($_POST['Page'])) {
?>
Page: <?php echo $_POST['Page'] ?>
<input type="hidden" name="Page" value="<?php $_POST['Page'] ?>" />
<?php
}
?>