<?php
/**
* TreeDropdown-like field that gives you a tree of items including an empty field, using ajax.
* Author: Marijn Kampf www.exadium.com
* Date: 24 Nov 2009
* Version: 2.0
* Revision date: 17 June 2010
* Changes: Updated to work with SilverStripe 2.4, tree function added.
*/
class OptionalTreeDropdownField extends TreeDropdownField {
private static $postTree = '</li></ul>';

/**
* Helper function to return the header (rather than defining same line twice).
*/
function preTree() {
   
return '<li id="0" class="l"> <a>' . _t('OptionalTreeDropdownField.NONE', "(None)", PR_MEDIUM, 'Non selected value of a dropdown') . '</a>';
}

/**
* Return the site tree
* For version 2.3 and earlier
*/
/*function gettree() {
echo $this->preTree();
parent::gettree();
echo $this->postTree;
}*/

/**
* Get the whole tree of a part of the tree via an AJAX request with empty / none item prepended.
*
* @param SS_HTTPRequest $request
* @return string
* for version 2.4 and later
*/
function tree($request) {
return $this->preTree() . parent::tree($request) . $this->postTree;
}
}
?>

   $f = new SimpleTreeDropdownField("PageLinkToID","Page link to", "SiteTree");
   $f->setHasEmptyDefault(true);