A GtkListItem is a container widget, derived indirectly from GtkBin and so only able to hold one direct child. Most of the time, the child you will want the list item to contain will be a GtkLabel - and so, in common with all objects that have an alternative '-with-label' constructor available in GTK, we have the option in PHP-GTK to pass the label's text as a parameter during construction, e.g.

<?php

$listitem = &new GtkListItem("This list item now has a label");

?>

<?php

$arrow = &new GtkArrow(GTK_ARROW_RIGHT, GTK_SHADOW_ETCHED_IN);
$listitem = &new GtkListItem();
$listitem->add($arrow);

?>

<?php

$box = &new GtkHBox();
$label = &new GtkLabel("Here we have multiple objects in a 
GtkListItem");
$arrow = &new GtkArrow(GTK_ARROW_RIGHT, GTK_SHADOW_ETCHED_IN);

$box->pack_start($label);
$box->pack_end($arrow);
$box->show_all();

$listitem = &new GtkListItem();
$listitem->add($box);

?>

Whatever your list item consists of, the GtkList will only respond to it as a GtkListItem. If you have different kinds of list item contents in the same list, you will need to exercise a great deal of caution if you are connecting callbacks to any form of select signal.

See also: GtkList, which has a working example under the constructor.