我正在开发一个 API，我希望能够知道何时添加或删除对象上的事件侦听器。原因是我正在触发的某些事件将要求我不断地轮询对象以获取更新，并且如果没有人在监听事件，我不想轮询对象。我正在轮询 html5 媒体播放器和其他播放器以缓冲更新，因此不需要轮询不是一种选择。我也不希望用户在添加或删除事件侦听器时必须调用函数来启动轮询。
我开发了一个解决方案，在将调用传递给闭包库之前拦截事件侦听器的添加，但这是一种非常hacky的做事方式，所以我想找到一种更好的方法。我将在下面发布我的方法，但我很想找到一种更好的方法来做到这一点。
正如我上面所说，我知道这是一种非常老套的做事方式，但这是我想出的唯一方法。随意删除sometechie.命名空间引用和/或在您正在处理的任何项目中使用任何或所有此代码。
/**
* @fileoverview Adds the ability to get events when an event listener is added or removed.
* @author Joshua Dwire
* @requires goog.events
*/
goog.provide('sometechie.eventhack');
goog.provide('sometechie.eventhack.GotListenerEvent');
goog.provide('sometechie.eventhack.LostListenerEvent');
goog.require('goog.events');
/**
* @class Provides a way to get events when an event listener is added or removed
*/
sometechie.eventhack={}
/**
* Generates the type of event that will be fired when a listener of the given type is added.
*
* @example goog.events.listen([src], sometechie.eventhack.generateGotListenerEventType([type]), [listener], [opt_capt], [opt_handler])
*
* @param {string} type Event Type.
* @returns {string} The type of event that will be fired when a listener of the given type is added.
*/
sometechie.eventhack.generateGotListenerEventType=function(type){
return '$sometechie.eventhack.gotlistener@'+type;
}
/**
* Generates the type of event that will be fired when the first listener of the given type is added.
*
* @example goog.events.listen([src], sometechie.eventhack.generateGotFirstListenerEventType([type]), [listener], [opt_capt], [opt_handler])
*
* @param {string} type Event Type.
* @returns {string} The type of event that will be fired when the first listener of the given type is added.
*/
sometechie.eventhack.generateGotFirstListenerEventType=function(type){
return '$sometechie.eventhack.gotfirstlistener@'+type;
}
/**
* Generates the type of event that will be fired when a listener of the given type is removed.
*
* @example goog.events.listen([src], sometechie.eventhack.generateLostListenerEventType([type]), [listener], [opt_capt], [opt_handler])
*
* @param {string} type Event Type.
* @returns {string} The type of event that will be fired when a listener of the given type is removed.
*/
sometechie.eventhack.generateLostListenerEventType=function(type){
return '$sometechie.eventhack.lostlistener@'+type;
}
/**
* Generates the type of event that will be fired when the last listener of the given type is removed.
*
* @example goog.events.listen([src], sometechie.eventhack.generateLostLastListenerEventType([type]), [listener], [opt_capt], [opt_handler])
*
* @param {string} type Event Type.
* @returns {string} The type of event that will be fired when the last listener of the given type is removed.
*/
sometechie.eventhack.generateLostLastListenerEventType=function(type){
return '$sometechie.eventhack.lostlastlistener@'+type;
}
/**
* Object representing a eventhack GotListener event.
*
* @param {string} type Event type.
* @param {Object} target
* @param {string} eventType listener type added.
* @param {boolean} gotFirst If this was the first listener added (there were no listeners before).
* @extends {goog.events.Event}
* @constructor
*/
sometechie.eventhack.GotListenerEvent = function(type, target, eventType, gotFirst) {
goog.base(this, type, target);
this.eventType = eventType;
this.gotFirst = gotFirst;
};
goog.inherits(sometechie.eventhack.GotListenerEvent, goog.events.Event);
/**
* The type of event that was added.
* @type {string}
*/
sometechie.eventhack.GotListenerEvent.prototype.eventType='';
/**
* If this was the first listener added (there were no listeners before).
* @type {boolean}
*/
sometechie.eventhack.GotListenerEvent.prototype.gotFirst=false;
/**
* Object representing a eventhack LostListener event.
*
* @param {string} type Event type.
* @param {Object} target
* @param {string} eventType listener type lost.
* @param {boolean} lostLast If the last listener was removed (there are no listeners anymore).
* @extends {goog.events.Event}
* @constructor
*/
sometechie.eventhack.LostListenerEvent = function(type, target, eventType,lostLast) {
goog.base(this, type, target);
this.eventType = eventType;
this.lostLast = lostLast;
};
goog.inherits(sometechie.eventhack.LostListenerEvent, goog.events.Event);
/**
* The type of event that was removed.
* @type {string}
*/
sometechie.eventhack.LostListenerEvent.prototype.eventType='';
/**
* If the last listener was removed (there are no listeners anymore).
* @type {boolean}
*/
sometechie.eventhack.LostListenerEvent.prototype.lostLast=false;
//Capture adding of event listeners
goog.events.$st_listen_overridden=goog.events.listen;
goog.events.listen=function(src, type, listener, opt_capt, opt_handler){
var eventSrc = /** @type {goog.events.EventTarget} */ src;
var hadListener=false;
try{
if(!goog.isArray(type) && !goog.isNull(type))hadListener=goog.events.hasListener(src,type);
}catch(e){}
var ret = goog.events.$st_listen_overridden.apply(this,arguments);
try{
if(!goog.isArray(type) && !goog.isNull(type)){
var hasListener=goog.events.hasListener(src,type);
var gotFirst=!hadListener&&hasListener;
if(gotFirst){
goog.events.dispatchEvent(eventSrc,
new sometechie.eventhack.GotListenerEvent(
sometechie.eventhack.generateGotFirstListenerEventType(type),
src,type,true));
}
goog.events.dispatchEvent(eventSrc,
new sometechie.eventhack.GotListenerEvent(
sometechie.eventhack.generateGotListenerEventType(type),
src,type,gotFirst));
}
}catch(e){}
return ret;
}
//Capture removing of event listeners
goog.events.$st_unlistenByKey_overridden=goog.events.unlistenByKey;
goog.events.unlistenByKey=function(key){
var src=null,type=null;
try{
if (goog.events.listeners_[key]){
var listener = goog.events.listeners_[key];
if (!listener.removed) {
src = /** @type {goog.events.EventTarget} */ listener.src;
type = listener.type;
}
}
}catch(e){}
var ret = goog.events.$st_unlistenByKey_overridden.apply(this,arguments);
try{
if(src!=null&&type!=null){
var lostLast=!goog.events.hasListener(src,type);
if(lostLast){
goog.events.dispatchEvent(src,
new sometechie.eventhack.LostListenerEvent(
sometechie.eventhack.generateLostLastListenerEventType(type),
src,type,true));
}
goog.events.dispatchEvent(src,
new sometechie.eventhack.LostListenerEvent(
sometechie.eventhack.generateLostListenerEventType(type),
src,type,lostLast));
}
}catch(e){}
return ret;
}