[news.eclipse.platform] Re: Communication between two plugins.

[Suvi Dhirakaosal <suviATcorelisDOTcom@xxxxxxxxxxxxxxxx>]

Walter,

Thank you very much for the explanation.  With little modification to 
the example source code, I got my test code to work as intended. :)

Regards,
Suvi D.

Walter Harley wrote:
> "Suvi Dhirakaosal" <suviATcorelisDOTcom@xxxxxxxxxxxxxxxx> wrote in message 
> news:ekg67f$vs8$1@xxxxxxxxxxxxxxxxxxxx
> > Hello all,
> >
> > I have been trying to get two plug-ins that I created/modified to do some 
> > basic communication for a few days (passing text).  From googling to 
> > searching the Eclipse newsgroups it seems that there are quite a few ways, 
> > and the most formal method is to use extensions/extension points.
> >
> > My setup is the following:
> >
> > Plug-in A with:
> > - extension point P
> > - interface I
> >
> > Plug-in B with:
> > - extension
> > - class C implementing I
> >
> > Now I'm at the point where I am trying to instantiate C within plug-in A 
> > and call the methods of I.
>
>
> The way you do it is with IConfigurationElement.createExecutableExtension(). 
> You get the IConfigurationElement from the platform registry - basically it 
> amounts to parsing the XML of the extension declaration.  What 
> createExecutableExtension() does is to reach into plug-in B, cause it to 
> instantiate a C, and then return it as an I.
>
> So, plug-in A *never ever* sees class C; it only ever sees an I.  But under 
> the covers it's actually a C, created by plug-in B's classloader.
>
> Here's a bit of sample code, excerpted from FactoryPathUtil in 
> org.eclipse.jdt.apt.core.  Sorry for the muddled indents.  In this case, 
> AnnotationProcessorFactory corresponds to your "I".  Note the "HERE'S YOUR 
> PAYLOAD" line, that's where you actually get your C.
>
>   IExtensionPoint extensionPoint = 
> Platform.getExtensionRegistry().getExtensionPoint(
>     AptPlugin.PLUGIN_ID, // name of plugin that exposes this extension point
>     "annotationProcessorFactory"); //$NON-NLS-1$ - extension id
>
>   // Iterate over all declared extensions of this extension point.
>   // A single plugin may extend the extension point more than once, although 
> it's not recommended.
>   for (IExtension extension : extensionPoint.getExtensions())
>   {
>    // Iterate over the children of the extension to find one named 
> "factories".
>    for(IConfigurationElement factories : 
> extension.getConfigurationElements())
>    {
>     if (!"factories".equals(factories.getName())) { //$NON-NLS-1$ - name of 
> configElement
>      continue;
>     }
>
>     // Iterate over the children of the "factories" element to find all the 
> ones named "factory".
>     for (IConfigurationElement factory : factories.getChildren()) {
>      if (!"factory".equals(factory.getName())) { //$NON-NLS-1$
>       continue;
>      }
>      try {
>       Object execExt = factory.createExecutableExtension("class"); 
> //$NON-NLS-1$ - attribute name
>       if (execExt instanceof AnnotationProcessorFactory){
>        //////  HERE'S YOUR PAYLOAD: apf = 
> (AnnotationProcessorFactory)execExt;
>       }
>      } catch(CoreException e) {
>       AptPlugin.log(e, "Unable to load annotation factory from plug-in"); 
> //$NON-NLS-1$
>      }
>     }
>    }
>   }