[Gwt-openlayers-devl] GWT-OL OpenLayersObjectWrapper

[Edwin C. <com...@gm...>]

Hi Michel,

What exactly are the doubts you have about OpenLayersObjectWrapper?

It extends JSObjectWrapper and wraps JSObject. JSObject is a class that adds
some functionality to JavaScriptObject. JavaScriptObject is the handle GWT
provides on Javascript objects (makes sense :-)....). For a deeper
understanding of JavaScriptObject and interacting with Javascript from GWT,
I would have to refer you to the GWT documentation. JSObject and other
classes from util help dealing with the Javascript/Java communication.

There are two ways to "wrap" a Javascript object:
a) provide a wrapper class that holds on to the Javascript object via the
handles GWT provides (in our case JSObject)
b) extend JavaScriptObject/JSObject directly, which GWT calls Overlay types

In GWT we have choosen for the first option. The only difference is that in
option (a) you do getJSObject() to get at the handle on the Javascript
object you are wrapping, while in option (b) you can access the handle on
your Javascript object via this.

Overlay types were not available when GWT-OL was created and I have a slight
favor for the explicit wrapping, as it makes it more clear that you are
"wrapping" something. It is a case of favoring Composition over Inheritance.
Also, then we do not need to do anything to hide methods defined on JSObject
to users.

OpenLayersObjectWrapper simply defines methods/properties that every
OpenLayers object will have, so these can be share by all classes wrapping
OpenLayers objects. Currently I it only has getClassName() and getEvents().
The latter is defined there because you also might want to test if a class
has an Events object (and fires events).

If you are wrapping a Javascript object and it is an OpenLayers object, then
you should extend OpenLayersObjectWrapper. If it is an OpenLayers object
that fires event, then you should extend OpenLayersEObjectWrapper. Otherwise,
you shouldn't extend OpenLayers(E)ObjectWrapper

StyleMap is an OpenLayers object so it would extend OpenLayersObjectWrapper.

If you do:
var sm = new OpenLayers.StyleMap();

Then you get an object with a CLASS_NAME. That is why it should be wrapped
by OpenLayersObjectWrapper.

Greetings,
Edwin





2009/8/21 Michel vitor <mic...@gm...>

> Dear Edwin,
>
> I'm trying to make a function in Measure OL  but I have a doubt about the
> class OpenLayersObjectWrapper and
> you could give me a description of their functionality
> because I need to create a class StyleMap.js.
>
> --
> Michel Vitor A Rodrigues
> 6° Periodo de Computação
> Grupo Intec,Viçosa MG
>
>