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Yahoo! UI Library

Event Utility  2.5.0

Yahoo! UI Library > event > EventProvider.js (source view)

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/**
 * EventProvider is designed to be used with YAHOO.augment to wrap 
 * CustomEvents in an interface that allows events to be subscribed to 
 * and fired by name.  This makes it possible for implementing code to
 * subscribe to an event that either has not been created yet, or will
 * not be created at all.
 *
 * @Class EventProvider
 */
YAHOO.util.EventProvider = function() { };

YAHOO.util.EventProvider.prototype = {

    /**
     * Private storage of custom events
     * @property __yui_events
     * @type Object[]
     * @private
     */
    __yui_events: null,

    /**
     * Private storage of custom event subscribers
     * @property __yui_subscribers
     * @type Object[]
     * @private
     */
    __yui_subscribers: null,
    
    /**
     * Subscribe to a CustomEvent by event type
     *
     * @method subscribe
     * @param p_type     {string}   the type, or name of the event
     * @param p_fn       {function} the function to exectute when the event fires
     * @param p_obj      {Object}   An object to be passed along when the event 
     *                              fires
     * @param p_override {boolean}  If true, the obj passed in becomes the 
     *                              execution scope of the listener
     */
    subscribe: function(p_type, p_fn, p_obj, p_override) {

        this.__yui_events = this.__yui_events || {};
        var ce = this.__yui_events[p_type];

        if (ce) {
            ce.subscribe(p_fn, p_obj, p_override);
        } else {
            this.__yui_subscribers = this.__yui_subscribers || {};
            var subs = this.__yui_subscribers;
            if (!subs[p_type]) {
                subs[p_type] = [];
            }
            subs[p_type].push(
                { fn: p_fn, obj: p_obj, override: p_override } );
        }
    },

    /**
     * Unsubscribes one or more listeners the from the specified event
     * @method unsubscribe
     * @param p_type {string}   The type, or name of the event.  If the type
     *                          is not specified, it will attempt to remove
     *                          the listener from all hosted events.
     * @param p_fn   {Function} The subscribed function to unsubscribe, if not
     *                          supplied, all subscribers will be removed.
     * @param p_obj  {Object}   The custom object passed to subscribe.  This is
     *                        optional, but if supplied will be used to
     *                        disambiguate multiple listeners that are the same
     *                        (e.g., you subscribe many object using a function
     *                        that lives on the prototype)
     * @return {boolean} true if the subscriber was found and detached.
     */
    unsubscribe: function(p_type, p_fn, p_obj) {
        this.__yui_events = this.__yui_events || {};
        var evts = this.__yui_events;
        if (p_type) {
            var ce = evts[p_type];
            if (ce) {
                return ce.unsubscribe(p_fn, p_obj);
            }
        } else {
            var ret = true;
            for (var i in evts) {
                if (YAHOO.lang.hasOwnProperty(evts, i)) {
                    ret = ret && evts[i].unsubscribe(p_fn, p_obj);
                }
            }
            return ret;
        }

        return false;
    },
    
    /**
     * Removes all listeners from the specified event.  If the event type
     * is not specified, all listeners from all hosted custom events will
     * be removed.
     * @method unsubscribeAll
     * @param p_type {string}   The type, or name of the event
     */
    unsubscribeAll: function(p_type) {
        return this.unsubscribe(p_type);
    },

    /**
     * Creates a new custom event of the specified type.  If a custom event
     * by that name already exists, it will not be re-created.  In either
     * case the custom event is returned. 
     *
     * @method createEvent
     *
     * @param p_type {string} the type, or name of the event
     * @param p_config {object} optional config params.  Valid properties are:
     *
     *  <ul>
     *    <li>
     *      scope: defines the default execution scope.  If not defined
     *      the default scope will be this instance.
     *    </li>
     *    <li>
     *      silent: if true, the custom event will not generate log messages.
     *      This is false by default.
     *    </li>
     *    <li>
     *      onSubscribeCallback: specifies a callback to execute when the
     *      event has a new subscriber.  This will fire immediately for
     *      each queued subscriber if any exist prior to the creation of
     *      the event.
     *    </li>
     *  </ul>
     *
     *  @return {CustomEvent} the custom event
     *
     */
    createEvent: function(p_type, p_config) {

        this.__yui_events = this.__yui_events || {};
        var opts = p_config || {};
        var events = this.__yui_events;

        if (events[p_type]) {
YAHOO.log("EventProvider createEvent skipped: '"+p_type+"' already exists");
        } else {

            var scope  = opts.scope  || this;
            var silent = (opts.silent);

            var ce = new YAHOO.util.CustomEvent(p_type, scope, silent,
                    YAHOO.util.CustomEvent.FLAT);
            events[p_type] = ce;

            if (opts.onSubscribeCallback) {
                ce.subscribeEvent.subscribe(opts.onSubscribeCallback);
            }

            this.__yui_subscribers = this.__yui_subscribers || {};
            var qs = this.__yui_subscribers[p_type];

            if (qs) {
                for (var i=0; i<qs.length; ++i) {
                    ce.subscribe(qs[i].fn, qs[i].obj, qs[i].override);
                }
            }
        }

        return events[p_type];
    },


   /**
     * Fire a custom event by name.  The callback functions will be executed
     * from the scope specified when the event was created, and with the 
     * following parameters:
     *   <ul>
     *   <li>The first argument fire() was executed with</li>
     *   <li>The custom object (if any) that was passed into the subscribe() 
     *       method</li>
     *   </ul>
     * If the custom event has not been explicitly created, it will be
     * created now with the default config, scoped to the host object
     * @method fireEvent
     * @param p_type    {string}  the type, or name of the event
     * @param arguments {Object*} an arbitrary set of parameters to pass to 
     *                            the handler.
     * @return {boolean} the return value from CustomEvent.fire
     *                   
     */
    fireEvent: function(p_type, arg1, arg2, etc) {

        this.__yui_events = this.__yui_events || {};
        var ce = this.__yui_events[p_type];

        if (!ce) {
YAHOO.log(p_type + "event fired before it was created.");
            return null;
        }

        var args = [];
        for (var i=1; i<arguments.length; ++i) {
            args.push(arguments[i]);
        }
        return ce.fire.apply(ce, args);
    },

    /**
     * Returns true if the custom event of the provided type has been created
     * with createEvent.
     * @method hasEvent
     * @param type {string} the type, or name of the event
     */
    hasEvent: function(type) {
        if (this.__yui_events) {
            if (this.__yui_events[type]) {
                return true;
            }
        }
        return false;
    }

};

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