Creating Extension Points

In Chapter 11, Creating Extension Points: How Others Can Extend Your Plug-ins, you learned how to define new extensions using extension points. The example defined in project com.ibm.jdg2e.extensionpoint demonstrates how to write a plug-in that offers the possibility for other plug-ins to extend it. This plug-in defines a common toolbar pulldown, conceptually similar to the Run > External Tools menu choice:

A second plug-in, defined in project com.ibm.jdg2e.extensionpoint.test, shows how to extend the first plug-in.

Running the Example

To run the example, launch the run-time instance of Eclipse (Run > Run As > Eclipse Application) from the Plug-in Development perspective. The contributed menu choices are shown from the toolbar menu pulldown (). If you have customized the perspective, you may need to explicitly add the "JDG2E: Tool Actions" action set (Window > Customize Perspective... > Commands).

Roadmap of the Example

As described above, this example is partitioned into two projects. All but the last class in this table are contained in the com.ibm.jdg2e.extensionpoint project.

Class (All) Description

IToolAction Interface that all tool action contributions to the com.ibm.jdg2e.extensionpoint.toolAction extension point must implement, that is, the class specified in the tool attribute of the <action> tag.

HelloWorldToolAction Quick test of implementation; action displays an information message.

ToolActionsPulldownDelegate Processes extension point contributions to com.ibm.jdg2e.extensionpoint.toolAction, handles menu choice selections from the common toolbar pulldown and delegates them to its associate tool action (IToolAction). Also registers as a register change listener (Platform.getExtensionRegistry().addRegistryChangeListener(IRegistryChangeListener) to support dynamically installed plug-ins.

ContributedTestToolAction Similar to HelloWorldToolAction, this is contributed by another plug-in, in project com.ibm.jdg2e.extensionpoint.test. It also displays an information message, and parses some of the parameters supplied as part of the IConfigurationElement interface.

References

FAQ 88: Can my extension point schema contain nested elements?
FAQ 100: How do I find out more about a certain extension point?
FAQ 114: How do I locate the owner plug-in from a given class?
FAQ 117: How do I make my plug-in dynamic enabled?
FAQ 118: How do I make my plug-in dynamic aware?

Class (All)	Description
`IToolAction`	Interface that all tool action contributions to the `com.ibm.jdg2e.extensionpoint.toolAction` extension point must implement, that is, the class specified in the `tool` attribute of the `<action>` tag.
`HelloWorldToolAction`	Quick test of implementation; action displays an information message.
`ToolActionsPulldownDelegate`	Processes extension point contributions to `com.ibm.jdg2e.extensionpoint.toolAction`, handles menu choice selections from the common toolbar pulldown and delegates them to its associate tool action (`IToolAction`). Also registers as a register change listener (`Platform.getExtensionRegistry().addRegistryChangeListener(IRegistryChangeListener)` to support dynamically installed plug-ins.
`ContributedTestToolAction`	Similar to `HelloWorldToolAction`, this is contributed by another plug-in, in project `com.ibm.jdg2e.extensionpoint.test`. It also displays an information message, and parses some of the parameters supplied as part of the `IConfigurationElement` interface.