$this is undefined in a class

[Peter Jay Salzman]

I have a very simple class: 2 variables, 3 methods. PHP is telling me that
$this is undefined in one of the functions, but is defined and has the
expected value in the other two functions.

In the code before, $this is defined in LinksClass() and navbarLinks(), but
not selectGroup(). I've never seen anything like this before. What could
possibly be causing this?

<?
require_once('classDatabase.php');
Class LinksClass
{
var $groups;
var $links;

function LinksClass()
{
$db = new DatabaseClass;
$tblLnkGrp = 'pbtbl_lnkgrp';
$tblLinks = 'pbtbl_links';

// Store linkgroups in array indexed by linkgroup id.
//
$db->query("SELECT * FROM $tblLnkGrp");
while ( $row = $db->fetchArray() )
$this->groups[$row['id']] = $row;

// Store links in array indexed by link id.
//
$db->query("SELECT * FROM $tblLinks");
while ( $row = $db->fetchArray() )
$this->links[$row['id']] = $row;

}

// Creates a select menu of the linkgroups. UNUSED
//
function selectGroup( $activeGroupId = '' )
{
echo '<pre>'; print_r($this); echo '</pre>'; exit;
$output = '<select name="lnkGrp">';

foreach ( $this->groups as $group )
{
$grpId = $group['id'];
$grpName = $group['name'];
$selected = ( $activeGroupId == $grpId ) ? 'selected="selected"' : '';
$output .= "<option value=\"$grpId\" $selected>$grpName</option>\n";
}

echo $output . '</select>';
}

function navbarLinks()
{
echo '<div id="nav-links">';
StartNavGroup();
NavGroupHeading(LINKS);

foreach ( $this->links as $lnk )
NavItem($lnk['url'], $lnk['text'], $lnk['title']);

EndNavGroup();
echo '</div> <!-- nav-links -->';
}
}

?>

[Oli Filth]

Peter Jay Salzman wrote:

I have a very simple class: 2 variables, 3 methods. PHP is telling me that
$this is undefined in one of the functions, but is defined and has the
expected value in the other two functions.

In the code before, $this is defined in LinksClass() and navbarLinks(), but
not selectGroup(). I've never seen anything like this before. What could
possibly be causing this?

<...SNIP CODE...>

Can you post some (short) example code of how you are using the class
and calling its methods?

--
Oli

[Peter Jay Salzman]

Oli Filth <ca***@olifilth.co.uk> wrote:

Peter Jay Salzman wrote:

I have a very simple class: 2 variables, 3 methods. PHP is telling me that
$this is undefined in one of the functions, but is defined and has the
expected value in the other two functions.

In the code before, $this is defined in LinksClass() and navbarLinks(), but
not selectGroup(). I've never seen anything like this before. What could
possibly be causing this?

<...SNIP CODE...>

Can you post some (short) example code of how you are using the class
and calling its methods?

It's a bit complicted (probably because I'm still inexperienced with PHP).

I'm writing a blog and store various things in session variables to cache
them so the database doesn't have to be constantly queried. Each page
includes code like:

if ( ! isset($_SESSION['links']) )
touchLinksSession();

function touchLinksSession()
{
$_SESSION['links'] = new LinksClass;
}

I have a page that lets me edit links. Here's code for that:
<td>
<input type="text" name="frmLnkTitle" class="text"
value="<?= @ $theLnkTitle ?>" />
</td>
<td>Group:</td>
<td><?php LinksClass::selectGroup($row['grpid']) ?></td>
<input type="submit" name="action" class="sub" value="editlnk" />
<input type="submit" name="action" class="sub" value="deletelnk"
onclick="return deleteConfirm();" />
</td>

Oh, actually, I think I see the problem. Instead of using

LinksClass::selectGroup($row['grpid'])

which doesn't construct the class, I should use:

$_SESSION['links']->selectGroup($row['grpid'])

which DOES construct the class. That's why $this wasn't defined. Holy cow.
I can't believe I spent over an hour hunting for this. :(

I'm glad you told me to post example code; it focused my eye on what I
should've been looking at: where the code used, rather than where the class
is defined. Valuable lesson learned.

Thanks!
Pete