function parameterFields()
{
$subsites = Subsite::accessible_sites('CMS_ACCESS_CMSMain');
$options = $subsites->toDropdownMap('ID', 'Title');
$subsiteField = new TreeMultiselectField('Subsites', 'Sites', $options);
$subsiteField->setValue(array_keys($options));
// We don't need to make the field editable if only one subsite is available
if (sizeof($options) <= 1) {
$subsiteField = $subsiteField->performReadonlyTransformation();
}
$fields = parent::parameterFields();
if ($fields) {
$fields->insertBefore($subsiteField, $fields->First()->Name());
} else {
$fields = new FieldSet($subsiteField);
}
return $fields;
}
