[OpenLayers-Dev] vector behavior

[Tim Schaub]

In case it helps in understanding the design, I'll include a little 
detail on a very simple example here.

http://dev.openlayers.org/sandbox/topp/almanac/examples/v2-fixed-http-gml.html

That example does about the same thing that the gml-layer.html example 
does.  Except it is more verbose.

Instead of creating a layer like:

var layer = new OpenLayers.Layer.GML("GML", "gml/polygon.xml");

The vector behavior example (v2-fixed-http-gml.html) does the following:

var layer = new OpenLayers.Layer.Vector2("GML", {
     strategy: new OpenLayers.Strategy.Fixed(),
     protocol: new OpenLayers.Protocol.HTTP({
         url: "gml/polygon.xml"
     }),
     format: new OpenLayers.Format.GML()
});

Looks horrible, right?  And the example name is so long and tedious as well.

The point is that the existing GML layer wraps up a bunch (well, a bit) 
of vector behavior into a single class.  The GML layer requests all data 
once (that's a strategy), it uses HTTP (that's a protocol), and it 
parses responses as GML (that's a format).

The new design separates strategy, protocol, and format.  A strategy is 
tied to a layer (it has a reference to a layer and can only be used with 
a layer).  A protocol is tied to a format (it has a reference to a 
format).  You can swap out the format for a protocol (in theory) and you 
can use a protocol in the absence of a layer.

The result is that we can use these parts elsewhere.  People can mix and 
match as they like.  We can develop new strategies, protocols, and 
formats independently - assumptions about how they are integrated 
doesn't need to be tied up in a layer.

Then, of course, we can make things convenient again.  The GML layer (if 
there is demand for one) can use a Fixed strategy, an HTTP protocol, and 
a GML format.  The WFS layer can use a BBOX strategy, a WFS protocol, 
and a GML format.  Etc.

Tim

Tim Schaub wrote:
> Hey-
> 
> Some may have already seen the proposal for new vector layer behavior.
> http://trac.openlayers.org/wiki/Proposal/VectorBehavior
> 
> This week, I'll be working on implementing a bit of this new design. 
> I'm focussed on an AtomPub protocol, an Atom format, and a somewhat 
> smartish BBOX strategy.
> 
> I've started putting stuff up in an "almanac" sandbox.  The one example 
> that shows it wired together is not that impressive - but it represents 
> a new design for giving vector layers behavior.
> 
> http://dev.openlayers.org/sandbox/topp/almanac/examples/vector2.html
> 
> I appreciate any ideas on the work.  I've got a deadline to get this 
> working by next Monday - so it will be hasty work for a while.
> 
> http://trac.openlayers.org/log/sandbox/topp/almanac/
> 
> I've also refactored the WFS stuff into a WFS protocol.  This is 
> completely untested and expected not to work currently.  If anybody is 
> interested in picking that up, sbenthall will be working on it this week 
> as well.
> 
> Tim
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