PhutilEventListener.php
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	<?php

	/*
	* Copyright 2012 Facebook, Inc.
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	/**
	* @group event
	* @stable
	*/
	abstract class PhutilEventListener {

	private $listenerID;
	private static $nextListenerID = 1;

	final public function __construct() {
	// <empty>
	}

	abstract public function register();
	abstract public function handleEvent(PhutilEvent $event);

	final public function listen($type) {
	$engine = PhutilEventEngine::getInstance();
	$engine->addListener($this, $type);
	}


	/**
	* Return a scalar ID unique to this listener. This is used to deduplicate
	* listeners which match events on multiple rules, so they are invoked only
	* once.
	*
	* @return int A scalar unique to this object instance.
	*/
	final public function getListenerID() {
	if (!$this->listenerID) {
	$this->listenerID = self::$nextListenerID;
	self::$nextListenerID++;
	}
	return $this->listenerID;
	}


	}