Listeners

[askdctm]

Hi All,

I was trying to understand what exactly are listeners.

Came across the article in link http://experience-aem.blogspot.in/2014/03/aem-cq-56-sample-editconfig-listener-for-drag-drop.html. But could not understand much.

If some one could provide a detailed explanation, it would be helpful.

[Lokesh_Shivalingaiah · Accepted solution]

Basically, listeners are in simple words nothing but an activity or a service that will be watching for an event and triggers it. As scott mentioned listeners can be used for xtype (ex: Do something on selecting a selection xtype), or a JCR events like NODE_CREATE, NODE_UPDATE etc...

You can refer those articles to get indepth details about the same.

[smacdonald2008]

In AEM - there are different type of listeners (aka -- event handlers). Knowing how to work with the different types is important. 

You can code listeners at the component level. That is - when creating a custom xtype - and someone selects a value from a drop-down control - an event handler is fired off. This is just a JS method. For example: 

listeners: {
                selectionchanged: {
                    scope:this,
                    fn: this.updateHidden
                }
            },
// called when a selection in the drop-down is made

updateHidden: function() {
    var val1 = this.linkType.getValue();
    this.linkText.setValue(val1);
}

To learn how to work with event handlers for components - see this AEM community article: 

https://helpx.adobe.com/experience-manager/using/dynamically-updating-aem-custom-xtype.html

2. A second type of event handler in AEM occurs at the JCR level - you can code JCR event handles. WHen a node in the JCR is changed - an event handler is fired off. To learn how to write these types of event handlers -- see this community article: 

https://helpx.adobe.com/experience-manager/using/events.html

3. Some parts of AEM - like the DAM - also have handlers. You can write an AEM DAM Handler. See: 

https://helpx.adobe.com/experience-manager/using/damhandler.html

or replication events:

https://helpx.adobe.com/experience-manager/using/replication_events.html

4. Of course - you can use standard HTML/JS events in AEM too. Like when someone clicks a button on a form - an AJAX request is send to the server. See: 

https://helpx.adobe.com/experience-manager/using/custom-sling-servlets.html