silverstripe-dms/code/cms/DMSDocumentAddExistingField.php

<?php

class DMSDocumentAddExistingField extends CompositeField {

	public $useFieldContext = true;

	function __construct($name, $title = null) {
		$this->name = $name;
		$this->title = ($title === null) ? $name : $title;

		parent::__construct(new TreeDropdownField('PageSelector', 'Add from another page', 'SiteTree', 'ID', 'TitleWithNumberOfDocuments'));
	}

	/**
	 * Force a record to be used as "Parent" for uploaded Files (eg a Page with a has_one to File)
	 * @param DataObject $record
	 */
	public function setRecord($record) {
		$this->record = $record;
		return $this;
	}
	/**
	 * Get the record to use as "Parent" for uploaded Files (eg a Page with a has_one to File) If none is set, it will use Form->getRecord() or Form->Controller()->data()
	 * @return DataObject
	 */
	public function getRecord() {
		if (!$this->record && $this->form) {
			if ($this->form->getRecord() && is_a($this->form->getRecord(), 'DataObject')) {
				$this->record = $this->form->getRecord();
			} elseif ($this->form->Controller() && $this->form->Controller()->hasMethod('data') 
					&& $this->form->Controller()->data() && is_a($this->form->Controller()->data(), 'DataObject')) {
				$this->record = $this->form->Controller()->data();
			}
		}
		return $this->record;
	}

	public function FieldHolder($properties = array()) {
		return $this->Field($properties);
	}

	public function Field($properties = array()) {
		Requirements::javascript(DMS_DIR.'/javascript/DMSDocumentAddExistingField.js');
		Requirements::javascript(DMS_DIR."/javascript/DocumentHtmlEditorFieldToolbar.js");

		return $this->renderWith('DMSDocumentAddExistingField');
	}

	/**
	 * Sets or unsets the use of the "field" class in the template. The "field" class adds Javascript behaviour
	 * that causes unwelcome hiding side-effects when this Field is used within the link editor pop-up
	 */
	public function setUseFieldClass($use = false) {
		$this->useFieldContext = $use;
	}
}