Home » Newcomers » Newcomers » Invoking plugins, plugin relationships
| Invoking plugins, plugin relationships [message #147781] |
Mon, 10 April 2006 16:29  |
Eclipse User |
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Originally posted by: ecc11718.yahoo.com
Apologies if this isn't the correct place. New to Eclipse development.
Plugin A creates extension point that Plugin B extends. Extension point
Java interface's package is exposed in Runtime of Plugin A's plugin.xml.
Plugin B lists Plugin A in Dependencies of its plugin.xml. Both plugins
are independent of the Eclipse UI framework. Plugin A has defined a
contract of interactions (in the interface) it asks other plugins to
fulfill, in this case, Plugin B.
I believe both plugin.xmls and schema are satisfied. Both projects can
find the other via their respective plugin.xmls. Now I want to invoke
Plugin B, in effect, its implementation class of Plugin A's interface -- I
want to do this inside Plugin A.
Reading Eclipse documentation, "host" (A) plugins invoke "extender" (B)
plugins via the host's interface, the host oblivious to the extender's
implementation. Is that accurate? Obviously, at some point, Plugin A's
classloader would find the implementor class as specified in Plugin B's
plugin.xml, but where does this actually happen in the code? I'd like to
test Plugin B's implementation through a Plugin JUnit (for now, residing
in Plugin A).
Can someone point me to a code snippet or provide one, or direct me to
resources on this topic? I've researched this a bit online and can find no
concrete examples.
Thanks,
-Steven
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| Re: Invoking plugins, plugin relationships [message #147790 is a reply to message #147781] |
Mon, 10 April 2006 18:20  |
| Eclipse User |
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Originally posted by: wharley.bea.com
"Steven" <ecc11718@yahoo.com> wrote in message
news:e6507c3989bf7de11f4108e8b6ad9164$1@www.eclipse.org...
> Apologies if this isn't the correct place. New to Eclipse development.
You're in exactly the right place.
> Plugin A creates extension point that Plugin B extends. Extension point
> Java interface's package is exposed in Runtime of Plugin A's plugin.xml.
> Plugin B lists Plugin A in Dependencies of its plugin.xml. Both plugins
> are independent of the Eclipse UI framework. Plugin A has defined a
> contract of interactions (in the interface) it asks other plugins to
> fulfill, in this case, Plugin B.
>
> I believe both plugin.xmls and schema are satisfied. Both projects can
> find the other via their respective plugin.xmls. Now I want to invoke
> Plugin B, in effect, its implementation class of Plugin A's interface -- I
> want to do this inside Plugin A.
>
> Reading Eclipse documentation, "host" (A) plugins invoke "extender" (B)
> plugins via the host's interface, the host oblivious to the extender's
> implementation. Is that accurate? Obviously, at some point, Plugin A's
> classloader would find the implementor class as specified in Plugin B's
> plugin.xml, but where does this actually happen in the code? I'd like to
> test Plugin B's implementation through a Plugin JUnit (for now, residing
> in Plugin A).
>
> Can someone point me to a code snippet or provide one, or direct me to
> resources on this topic? I've researched this a bit online and can find no
> concrete examples.
The part up to where you ask "is that accurate" is accurate :-) Plug-in A,
itself, is not going to be able to see or create any of B's classes. To do
that, A would have to depend on B, which it can't, because B depends on A.
Instead, A is going to ask the platform to create a class from B on A's
behalf. That class will be visible to A only as an instance of the
interface. That is, if the interface is named IFoo, and B contains a class
Foo that implements IFoo, A will only ever see an IFoo (even though under
the covers what it has is a Foo). Foo is not available to A's classloader!
The platform method that you call to do this is
IConfigurationElement.createExecutableExtension(). You get the
IConfigurationElement from a call to IExtension; you get the IExtension from
a call to IExtensionPoint; you get the IExtensionPoint from
Platform.getExtensionRegistry().
For concrete examples, just find a plug-in that exposes an extension point,
and search its source code for createExecutableExtension(). Be aware that
since the plug-in framework is a very old part of the Eclipse code, the APIs
have changed a bit over time, so try to find a relatively new or at least
up-to-date example.
I imagine that this is documented somewhere in the online help. But
personally, I learned about it in the book "Eclipse: Building
Commercial-Quality Plug-ins" (Addison-Wesley; ISBN of the new edition:
032142672X), which I would recommend.
HTH,
-Walter Harley
BEA Systems, Inc.
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