Re: [e4-dev] Some random thoughts after browsing the e4 code base

[John Arthorne <John_Arthorne@xxxxxxxxxx>]

>4. What is the use of OSGi services in e4? So
far I have seen there is
>an IEclipseContext which allows you to fetch services like the old
>IServiceLocator in 3.x does. What about putting more services directly
>into OSGi (that are not local to any part of the workbench)? I would
put
>my declarative services to more use depending on the workbench services
>available.

Yes, that is certainly the intent: services
not local to a specific part are obtained as OSGi services. OSGi services
can be obtained through an IEclipseContext, and this is used in a few places
in e4 (for example IWorkspace is obtained as a service in the e4 photo
demo). Using the context for lookup allows overriding of how the service
lookup is done. By default it will doing a regular OSGi service lookup,
but more local contexts could override this to do a more specific lookup
(for example adding an LDAP filter), or even provide a service implementation
that isn't available in the framework service registry. Generally the services
are bound to the application code by injecting a context into an object,
rather than by directly referencing IEclipseContext, which avoids direct
dependency on e4-specific API. There is also some use of declarative services
in e4, but there are likely more places where we could take advantage of
it. We're still getting the hang of this programming model, so if you see
specific opportunities for using OSGi services where we currently aren't,
please enter a bug report.

John

Philipp Kursawe <phil.kursawe@xxxxxxxxx>
Sent by: e4-dev-bounces@xxxxxxxxxxx

07/22/2009 06:19 AM

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Subject	[e4-dev] Some random thoughts after browsing the e4 code base

Hello all,

I hope its ok for non-contributors to post on this list?

I thought I might get some more information about how e4 is supposed to
work (I have no idea what all this modeling is doing though) and checked
out the newest HEAD. Some random thoughts I would like to share with you:

1. Why is e4 still using an (empty) Activator in almost every project?
Shouldn't it be a good OSGi citizen and use the
FramworkUtil.getBundle(Class) whenever the current Bundle/BundleContext
is needed? Also the Activator.ID is error prone to refactoring, thats
why I never use it in my own projects.
A similar problem has the NLS feature of Eclipse PDE, when it creates 
the Messages class and puts the BUNDLE into a string rather to have
NLS.initialize(Messages.class.getPackage().getName() + ".messages",
Messages.class)

2. Why are you still using Require-Bundle in almost every bundle when a
I-P would do just fine? And then the CSS core bundle is requiring the
batik bundle which it does not use one class from, does it?

3. The CSS bundles are too tightly coupled with each other. As far as I
understand the concept, there are handlers for CSS elements. Couldn't
those handlers and other components that make up a CSS engine
implementation be contributed by extensions?

4. What is the use of OSGi services in e4? So far I have seen there is
an IEclipseContext which allows you to fetch services like the old
IServiceLocator in 3.x does. What about putting more services directly
into OSGi (that are not local to any part of the workbench)? I would put
my declarative services to more use depending on the workbench services
available. For instance, now in 3.5 I export the IWorkbench as a service
myself and have my other services consume it. Similar to the
ISelectionService, IProgressService and others.

5. I actually like the idea of being able to define the layout of RCP
applications. Currently I have gone through great pain to have a custom
view on top of each perspective that you can not close/move or whatever.
It provides a kind of "startbar" with custom gradient background.
See here:

Please understand my points not as criticism purely, I am sure for a lot
of things there are good reasons just unknown to me.

Said that, I am more than willing to contribute to e4 if possible after
I got more insight on the processes going on.

Keep up the good work!

Cheers,
Phil

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