[news.eclipse.tools] Re: publishing extension points - help!

["ted stockwell" <ted.stockwell@xxxxxxxxxx>]

That was an excellent explanation.
Thanks very much.

ted

"Vlad Klicnik" <klicnik@xxxxxxxxxx> wrote in message
news:3B81303F.F109F61D@xxxxxxxxxxxxx
> The argument on the createExecutableExtension refers to the attribute name
in
> your plugin.xml extension markup that specifies
> the name of a Java class implementing the extension. Let's take a look at
a
> concrete example.
>
> The Eclipse workbench defines an extension point
"org.eclipse.ui.importWizards"
> for adding new import wizards. The Eclipse workbench specifies that all
new
> implementations of an import wizard must implement
org.eclipse.ui.IImportWizard
> interface. It also specifies the "shape" of the extension markup for
import
> wizards. Below is an example.
>
>    <extension point="org.eclipse.ui.importWizards">
>       <wizard
>          id="com.xyz.ImportWizard1"
>          name="XYZ Web Scraper"
>          class="com.xyz.imports.ImportWizard1"
>          icon="./icons/import1.gif">
>          <description>
>             A simple engine that searches the Web and imports files
>          </description>
>          <selection class="org.eclipse.core.resources.IResource"/>
>       </wizard>
>    </extension>
>
> As part of the extension markup, the workbench expects <wizard
class="..."> to
> specify the implementation class being added to the workbench as the new
import
> wizard. The rest of the attributes are for the most part used to describe
how
> the new wizard will appear in the UI (ie. labels, icons, etc). So at
startup the
> workbench would retrieve all the import wizars extension defined in the
> plugin.xml (by calling the IPluginRegistry). It constructs its UI, and
keeps
> track of which UI element (ie. import wizard selection) corresponds to
which
> extension definition. So when the user picks a specific import wizard, the
> workbench has the corresponding IConfigurationElement that actually
represents
> the desired import wizard extension.
>
> The workbench would then do
>
> IImportWizard wiz = (IImportWizard)
> selectedCfig.createExecutableExtension("class");
>
> The workbench knows it is expecting IImportWizard so it can declare a
variable
> of this type, and do the cast (real code would have some error handling to
> handle bad extensions (case exceptions, etc)). The workbench knows it is
> expecting the markup to contain <wizard class="..."> so it specifies
"class" as
> the argument. It so happens the above markup uses the string "class" as
the
> attribute name, but it could have been anything else, like
"implementation",
> "wizardClass", or any other attribute name). The implementation of
> createExecutableExtension looks up the value of the attribute in the
config
> element (get "com.xyz.imports.ImportWizard1" in the above example), loads
that
> Java class (Class.forName(...)) and creates an instance of it
(c.newInstance())
> using default constructor. So to answer your question,
createExecutableExtension
> does not know it is creating an instance of IImportWizard. But the
workbench
> does and casts it as such.Once cast to the actual type, the workbench then
> interacts with the new object using the "contract" defined by the
IImportWizard
> interface.
>
> Hope this helps ... this same pattern (with variations) is repeated for
handling
> of all extension points in Eclipse (workbench, or any other).
>
> > Hi Vlad,
> >
> > >
> > > IFoo someFoo = (IFoo) cfg[0].createExecutableExtension("fooclass");
> > >
> >
> > I have some more questions if you don't mind...
> >
> > What is "fooclass" in the call above (the docs say it is the name of a
> > property but I don't get what property they're talking about)?
> > And how does the createExecutableExtension method know to create an
instance
> > of the IFoo class from the configuration element?
> >
> > Thanks in advance,
> > ted stockwell
>