[jbosside-dev] Extension Point best Practices

[Max Rydahl Andersen]

Just updating this thread so i matches my understanding of extension  
points ;)

> paulweb515 had 3 suggestions:
> <paulweb515> rawblem: I've seen 3 common usages
> <paulweb515> rawblem: 1) Tell you users to implement IPackageType that  
> has
> setId(*) as well as getId(*) ... then you can set your user's data when  
> you
> create the executable extension
>
> If you just let the extender implement IChef, he'll be filling in id and
> label twice, once in the extension point, and once in API.
> So paulweb suggests setters, but that's not a great idea because then  
> anyone
> who gets a reference to your object can
> change the ID and label. Obviously that's a glaring error.

There should be no setters in the required interface if you don't need to  
change it.

> <paulweb515> rawblem: 2) Like ViewPart, create an abstract base class  
> that
> they must use instead of just an interface.  ViewPart uses
> setInitializationData(*) to store the config element for the client to  
> use
> in a protected  method, and extracts id, label etc into the base abstract
> class ... but they're private, and it only provides public final String
> getId() so they can't change it
>
> This sounds like the best way, I'll look at it momentarily.

This is the most flexible setup. Note that the setInitializationData is
actually from IExtensionExecutable and it is a way for user classes to
*optionally* be told what is actually inside the plugin definition.

Thus the IViewPart has the getId() but the user could just implement
that by hardcode a value in the getter....AbstractViewPart then ensures
via IExtensionExecutable to setup the IViewPart contract to return the
correct value.

> <paulweb515> or 3) don't store the ID in the object, have that ID be  
> part of
> an association that your extension point knows.
>
> Not exactly the best way, because then given an IChef, you cannot get  
> his id
> or label.

Makes perfect sense if the id value is something not needed all the time;  
e.g.
fastViewWidthRatio for a ViewPart.

> All are welcome to give forth their suggestions or other best practices  
> they
> use WRT extension points ;)
> I'll probably be using a methodology similar to the one paulweb515
> suggested.

Having an interface and require users to extend a concrete abstract class  
instead
is a design flaw because then the interface is just dead code.

-- 
--
Max Rydahl Andersen
callto://max.rydahl.andersen

Hibernate
max at hibernate.org
http://hibernate.org

JBoss a division of Red Hat
max.andersen at jboss.com