Extending dojo.gfx.Group with default instanciated shapes - oop

Question

I'm attempting to create some simple UI components with dojo.gfx. I've managed to extend dojo.gfx.Group, but am out of my depth getting any of the default shapes drawn to the surface. Inspecting the rendered SVG in Firebug, there's rightfully a node but no rect.
The simplified class looks like this:
dojo.provide("gfxui.SimpleButton");
dojo.require("dojox.gfx.shape");//-¿ needed?
dojo.require("dojox.gfx.svg");
dojo.require("dojox.gfx._base");
dojo.declare("gfxui.SimpleButton", dojox.gfx.Group, {
constructor: function(){
this.draw();
},
draw:function(){
var bg = this.createRect(this.rect_props);
//var bg = this.createObject(dojox.gfx.Rect);
}
}
gfxui.SimpleButton.nodeType = dojox.gfx.Group.nodeType;
dojo.extend(dojox.gfx.Surface, {
createButton: function(){
var button = this.createObject(gfxui.SimpleButton, null, true);
this.add(button);
return button;
}
});
And the javascript in the HTML looks like this:
dojo.require("dojox.gfx");
dojo.require("gfxui.SimpleButton");
function init(){
var g = dojox.gfx;
var surface = dojox.gfx.createSurface(dojo.byId("gfx_holder"), 800, 280, "#eee");
var button = container.createButton();
};
dojo.addOnLoad(init);

Answer 1

I prefer a simple augmentation technique. Below is the content of a script tag:
// let's include gfx (renderer will be selected dynamically)
dojo.require("dojox.gfx");
// useful short names
var d = dojo, g = dojox.gfx;
// our creator function
function createButton(color){
// let's create our main shape: group
var group = this.createGroup();
// add custom properties, if any
group._rect = group.createRect().
setShape({x: 5, y: 5, width: 100, height: 30}).
setStroke("black").
setFill(color);
return group;
}
// we want it to be available on groups and surfaces
d.extend(g.Surface, {createButton: createButton});
d.extend(g.Group, {createButton: createButton});
// let's test the result
dojo.addOnLoad(function(){
var s = g.createSurface(dojo.byId("surface"), 500, 400),
b = s.createButton("red");
});
The example above assumes that there is a <div> called "surface".
The augmentation technique works for any renderer regardless its implementation, and uses only published APIs.