On 10/10/07, Fabio Mancinelli < fabio.mancinelli@xwiki.com> wrote:

Dear all,

I am starting to take a deeper look at XEclipse and I think there are
some improvements at the design level that, IMHO, are worth to be
taken into account.
These improvements leverage Eclipse platform's features that, to some
extent, have been re-implemented in XEclipse.

Yes, this is very likely since myself and Tharindu did not have much experience with Eclipse Plugin Development when we started off XEclipse. A similar situation occurred with dynamic proxies and Catalin helped us out.

1) Deferred tree content managers.
I am a big fan of this feature and I tend to use it whenever I can.
Basically a deferred tree content manager allows you to "fetch" tree
children in a deferred way.
One example is the "SVN Repository" or "CVS Repository" views in your
Eclipse IDE. When you expand a node it displays a "Pending..." element
and, when the fetching job is over, the actual elements ( i.e., files
and directories available on the repository) are displayed.

The same mechanism could be used in XEclipse to fetch Spaces and Pages.

The good thing about this approach is that the manager takes care of
everything:
* A tree node that is collapsed before the fetching job is terminated
deletes the corresponding job;
* Changing the input element of the tree invalidates all the active jobs
* You can expand different tree nodes without waiting that the
previous ones terminate their fetching job: in this case you will
have several "Pending..." indicators in the tree.

You can play a bit with the "SVN Repository" view and see what I mean.
The best news is that all of this already implemented and available
in the eclipse platform through the DeferredTreeContentManager[1] class.

Using the deferred tree content fetching mechanism eliminates the
need of having additional logic in XWikiSpace for understanding when
pages are ready (i.e., all the code that manages isPagesReady in
XWikiSpace.java). You will simply have a method getPages that could
take possibly forever and that directly fetches the pages from the
XMLRPC source (or from the offline cache).

I think that this will also have impact on the Decorators that are
used to wrap XWiki* elements in order to provide a visual feedback on
what's going on (i.e., all the GuiUtils.runOperationWithProgress will
be unnecessary since the deferred tree content manager will take care
of everything)

2) Adapters
I noticed that there is a TreeAdapter interface that basically is
used for providing labels, children and so on.
All classes that can be "displayed" in a tree implements this
interface (i.e., XWikiConnection, XWikiPage, XWikiSpace).

I think that this "pollutes" the model because, for example, getPages
and getTreeChildren basically return the same thing and, therefore,
are duplicated methods. Moreover in this way you put "GUI"-oriented
stuff in the model and this is not good.

The Eclipse platform has a mechanism for providing adapters that are
able to give information about model elements to GUI components[2].
Not surprisingly they are called Adapters and are handled via
extension points. Basically you register an AdapterFactory that
provides IWorkbenchAdapters.
An IWorkbenchAdapter[3] actually contains what was declared in
XEclipse TreeAdapter.

When you need structural information about an object, you can then
query the platform for an adapter that matches a given interface and
is suitable for a given object. In our case I can register an adapter
for XWikiSpace that implements the getChildren method and that will
simply call the getPages method of the XWikiSpace model object.

In this way I can clearly separate the "GUI" code from the "model"
code and leave Eclipse handle the rest.

It is worth to notice that many GUI content providers directly
support IWorkbenchAdapters out of the box, so if you carefully write
your model adapters you will never have to write a content/label
provider; but even when you write your own content provider you can
always put a lookup to the adapter and then talk to it for getting
the information to display (this is actually a standard practice).

In the attachment you can find a sample implementation of the
"deferred tree" way of displaying the XWiki navigator that makes use
of adapters.
Notice the getChildren methods in XWikiSpaceAdapter (declared in
AdapterFactory.java). It calls a method myGetPages that I've added
for testing purposes to the IXWikiSpace interface and that basically
does the following straight simple thing:

public Collection<IXWikiPage> myGetPages() throws
ConfluenceException, SwizzleConfluenceException {
   Confluence rpc = getConnection().getRpcProxy();
   String spaceKey = getKey();
   List<Object> pages = rpc.getPages(spaceKey);
   List<IXWikiPage> result = new ArrayList<IXWikiPage>();
   for (int i = 0; i < pages.size(); i++) {
     PageSummary pageSummary = (PageSummary) pages.get(i);
     XWikiPage xWikiPage = new XWikiPage(this, pageSummary);
     result.add(xWikiPage);
   }

   return result;
}

+1 to all changes. I think I can learn a lot along the way.

Of course this is a proposal to discuss about.
But I think that we should spend some time on it because we could end
up with a lighter design and a more maintainable product.

WDYT?

Cheers,
Fabio

Thanks a lot.

- Asiri

[1] http://help.eclipse.org/help33/index.jsp?topic=/
org.eclipse.platform.doc.isv/reference/api/org/eclipse/ui/progress/
DeferredTreeContentManager.html
[2] Of course the adapters mechanism is not limited to GUI components
but can be used to adapt an object to whatever interface we need to.
[3] http://help.eclipse.org/help33/index.jsp?topic=/
org.eclipse.platform.doc.isv/reference/api/org/eclipse/ui/model/
IWorkbenchAdapter.html

These are the XML lines in plugin.xml that defines the
org.eclipse.core.runtime.adapters extension point for registering the
AdapterFactory and types:

<extension point="org.eclipse.core.runtime.adapters">
   <factory
      adaptableType="org.xwiki.plugins.eclipse.model.IXWikiConnection"
      class=" fm.AdapterFactory">
     <adapter
type="org.eclipse.ui.progress.IDeferredWorkbenchAdapter"></adapter>
   </factory>
   <factory
      adaptableType="org.xwiki.plugins.eclipse.model.IXWikiSpace "
      class="fm.AdapterFactory">
     <adapter
type="org.eclipse.ui.progress.IDeferredWorkbenchAdapter"></adapter>
   </factory>
</extension>

_______________________________________________
devs mailing list
devs@xwiki.org
http://lists.xwiki.org/mailman/listinfo/devs