Events « SwellJS – another big fish in the sea

Posts Tagged ‘Events’

by SleepyCod

4 Sep 09

Even more Drag&Drop coolness between your desktop and your browser!

We are making more & more progress with the native DnD API, and being native means fully taking advantage of Event Bubbling.

In essence this means that if you want to make for example a datatable with a lot of rows without attaching events to them (remember the flyweight pattern?) you’ll only need to set your draggable element at a higher level in the hierarchy to get the DnD behavior applied on all children nodes (marked with the draggable attribute), that’s powerful and of course, reduces a lot the memory footprint of your web application.

A lot of components could benefit of this approach, Treeview, Datatable, Listview and so on.

Another part of the example shows another level of interaction between the browser and desktop, and we are sure this one will get a lot of attention and excitement!

And the code

var proxyElement = html.div(null, html.span({
    'cls' : 'dd-proxy-icon'
}), html.span('Moo'));
 
 
var draggableRows = new Swell.Lib.DD.Draggable('bleh', {
    'delegate' : true,
    'proxy'  : true,
    'proxyOverride'    : proxyElement,  
    'dataCallback' : function(dt) {
        var _currentEl = this.getDragEl().current(), _stdOut = [];
 
        for(var _n = 0, _l = _currentEl.childNodes.length; _n < _l; _n++) {
            if(_currentEl.childNodes[_n].nodeType === 1) {
                var _text = $(_currentEl.childNodes[_n]).text();
                _stdOut.push(Swell.Core.trim(_text));
            }
        }
        this.setData(dt, 'text/plain', _stdOut.join("\t"));
    }
});
 
var dropTarget = new Swell.Lib.DD.Droppable('moo');
 
dropTarget.ondrop = function(e, draggable) {
    if(!!draggable) {
        draggable.getDragEl().appendTo($('moo').current().tBodies[0]);
    }
}

2 Comments , Tags: drag&drop, event delegation, Events, Javascript, Swell

by SleepyCod

13 Mar 09

Painless publish/subscribe system with swell’s custom events

Posted in Javascript, Swell

Let me start with wikipedia’s own publish/subscribe pattern definition : Publish/subscribe (or pub/sub) is an asynchronous messaging paradigm where senders (publishers) of messages are not programmed to send their messages to specific receivers (subscribers). This decoupling of publishers and subscribers can allow for greater scalability… We absolutely wanted to have this pattern implemented into Swell as we are fervent supporters of the SoC. The goal was to be able to hook the Custom event model to potentially any class as well as using custom events outside of a class context.

Custom event model

By inheriting the CustomEventModel class built-into swell, the children class is augmented with new methods and collections brought from the model. Example :

    Swell.Core.Class({
        name        : 'Hashtable',
        namespace   : 'Swell.Core',
        inherits    : [Swell.Core.Enumerable, Swell.Core.CustomEventModel],
        ...

Swell.Core.Hashtable class now have those methods :

createEvent (creates a custom event that is bound to the class ex : onHashUpdated)
fireEvent (fires desired event and will notice all the subscribers aka execute callback functions)
subscribe (subscribe to a custom event of the class from/outside the class)
unsubscribe
getEvents

In the hashtable code, we use custom events to update a static property containing the length.

var _initEvents = function() {
    /**
      * Initialization of the event
      * @event onChange fires when an item is added/updated in the hashtable
    */
    this.createEvent('onHashUpdated');
    this.subscribe('onHashUpdated', _updateLength); //_updateLength is a private function of the class
}
...
/**
 * Now triggering the event
*/
set : function(key, value) {
    if(arguments.length === 1) {
        _hash[Swell.uniqueId()] = key;
    } else {
        _hash[key] = value;
    }
    this.fireEvent('onHashUpdated', this);
    return this;
},
...

Standalone custom events

This is the simplest way of using the custom event system.
In the example below we have created a basic object called button that makes use of custom events.

var button = function() {
    var value = 1;
 
    this.setValue = function(val) {
        value = val;
        this.onValueChange.fire();
    };
 
    this.onValueChange = new Swell.Core.CustomEvent('onValueChange');
}
 
var handler = function() {
    alert('button value has changed');
}
 
var btn = new button();
btn.onValueChange.subscribe(handler);
btn.setValue('toto');