Creating Extension Points¶

In the Plug-in Manifest Editor’s Extension Point tab, new extension points can be declared. In addition, the plugin.xml file can be edited by hand to declare new extension points.

Plug-in Manifest Editor

• Open Plug-in Manifest Editor (double click on plugin.xml)
• Click Extension Point tab
• Click Add button
• Enter ID - this is appended to your plugin id to form a fully qualified identification for the extension point
• Enter Name (human reading purposes)
• Click Finish

The extension-point schema defines how to parameterize extensions.

Extension-point Schema

The extension-point schema defines how to parameterize extensions. An extension-point schema can be edited by hand or using Eclipse’s extension-point schema editor.

See Eclipse help guide for detailed instructions on editing extension-point schemas.

To create a extension-point schema that requires a extension to implement an interface:

• Create an extension-point as described above.
• If extension-point schema editor does not open. Open it. (double click on the new .exsd file)
• Click new Element button
• In the properties view click on the Name property and enter a name for the element. It should be logical. Parser is a good example.
• Ensure Parser is selected in editor and click the New Attribute button
• In properties view change Name to class.
• In properties view change Kind to java
• In properties view change Based On to “name of Interface”. Remember to include package name.
• (Not required) In properties view change Name to id.
• (Not required) Create a Name attribute
• Select extension in Editor
• Right click on Sequence under Element Grammar Heading
• Select New->Reference->”Name of Created Element”

Done.

Finding Extensions¶

The following classes demonstrates how to find registered extensions:

import org.eclipse.core.runtime.IConfigurationElement;
import org.eclipse.core.runtime.IExtension;

public interface IProcessMember {
    public Object process(IExtension extension,
      IConfigurationElement member);
}

This class is a visitor.

import org.eclipse.core.runtime.IConfigurationElement;
import org.eclipse.core.runtime.IExtension;
import org.eclipse.core.runtime.IExtensionPoint;
import org.eclipse.core.runtime.IExtensionRegistry;
import org.eclipse.core.runtime.Platform;

public class ProcessExtensions {
 public static void process(String xpid, IProcessMember processor) {
        IExtensionRegistry registry = Platform.getExtensionRegistry();
        IExtensionPoint extensionPoint =
            registry.getExtensionPoint(xpid);
        IExtension[] extensions = extensionPoint.getExtensions();
        // For each extension ...
     for (int i = 0; i < extensions.length; i++) {
            IExtension extension = extensions[i];
         IConfigurationElement[] elements =
              extension.getConfigurationElements();
            // For each member of the extension ...
         for (int j = 0; j < elements.length; j++) {
                IConfigurationElement element = elements[j];
             processor.process(extension, element);
            }
        }
    }
}

This class is used to process extensions as identified by an id. An id and a visitor are passed to the process method. The visitor knows the class that uses the extension.