eclipse plug in development
(Page 2)
A Mechanism For Extensibility
Figure 1-7
We all know that eclipse is extensible. In order to achieve this
extensibility eclipse uses the concept of extension points and
extension. Think of extension point as Electric socket and think of
extension as a plug. Plug-in A exposes a extension point (electric
socket) which Plug-in B extends by providing an extension (an electric
plug). Plug-in A knows nothing about plug-in B. If we think about it
this is very similar to concept of Inheritance – we extend functionality
of base class to provide more specific implementation. Think of Plug-in
A as a text editor and Plug-in B as xml editor. Text editor declares
extension point thereby declaring to the world that it is open for
extension and xml editor extends text editor by using its extension
point to customize it in its own way. It is important to understand that
each extension point essentially declares
a contract. An extension point provider only accepts those extensions
which abide by the contract.
These extension points and extensions are declared in plugin.xml
(discussed earlier). The runtime is able to wire extensions and
extension points and form a registry using markup alone.
Plug-in Example
Now that we have covered good amount of architecture basics, its time to
get our hands dirty with some actual plug-in coding. The process for
creating a plug-in is best demonstrated by implementing a plug-in on
which discussion and examples can be based. Here we will take a
step-by-step approach to create a simple but fully operational plug-in.
This example will try to give you an feel of eclipse plug-in
development. However, don’t try to grab all the details at this point.
It is fine if you are not able to understand much of the details in this
example. Rest of the tutorial will cover all the topics in great depth.
We will build a simple Resource Manager plug-in. Features of this
plug-in are as follows:
- Ability to add/remove resources (essentially files in workspace)
to resource manager.
- Display list of resources which were added to resource manager.
- Ability to open up associated editor whenever resource is
clicked.
Note: All Examples in this tutorial have been implemented using
Eclipse version 3.1.2
Creating a Plug-in
1. Launch Eclipse.
2. From File menu, select New Project. This will open up New Project
wizard.
3. Now select Plug-in Project and click on the next button. (see
Figure 1-8)
Figure 1-8
4. On next page of the wizard (see Figure 1-9), enter the name of the
project "com.myplugin.rmp"
Figure 1-9
5. Fill in the other fields as shown and then click the Next button. The
next wizard page displays options for generating plug-in Java class.
Fill all the fields as shown below. Do not fill anything in classpath
field - This has been removed in eclipse 3.4. Plug-in Activator is
required if we want to do anything on plug-in start up or shut down. For
example we want to acquire some resources at plug-in start up and
perform clean up when plug-in is shutdown. It is important to note that
Eclipse startup does not essentially means that your plug-in is starting
up. Plug-ins are loaded/started only when they are demanded or required.
So activator is used when plug-in startup/shutdown happens.
Figure 1-10
6. Click Next, select Plug-in with a view and then click the Next
button.
Figure 1-11
7. Next, Enter the values for this page (see Figure 1-12), and click the
Next button.
Figure 1-12
8. Finally, uncheck all the options (see Figure 1-13). and click Finish
button.
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