Eclipse 3.0 adapter issues

Last modified: February 16, 2004

This document outlines proposed changes in the 3.0 timeframe to the IAdapterManager infrastructure. Related bug reports contain much of the rationale and discussion:

Current limitations

Nothing is known about an adapter factory until the plugin that provides the adapter is loaded. This makes it difficult to calculate if an action contribution or refactoring participant may potentially be applicable for a given selection until it is executed.
The current API only supports returning a single adapter for a given adaptable type. For example, only one factory is allowed to adapt IFile to IPropertySource. In some contexts, it is appropriate to obtain all possible adapters on a type. Several plug-ins may want to supply an IPropertySource or an IActionFilter for IFile.

Proposed solution

Add the following three new methods to IAdapterManager:

public boolean hasAdapter(Object adaptable, String adapterTypeName);
public Object getAdapter(Object adaptable, String adapterTypeName);
public Object[] getAdapters(Object adaptable, String adapterTypeName);

getAdapter returns the first non-null adapter found as it does today (transitive search of superclasses and then super-interfaces). getAdapters returns all adapters for all superclasses and interfaces of the supplied object. Only factories belonging to loaded plug-ins will be consulted by the getAdapter* methods. hasAdapter consults both loaded and unloaded factories.

A new "adapters" extension in the runtime plug-in will specify the name of the factory class, removing the need for plug-ins to explicitly register their adapters on startup (they would be lazily registered on the first lookup on that factory after the plug-in is loaded):

<extension point="org.eclipse.core.runtime.adapters">
   <factory 
	class="org.eclipse.jdt.internal.ui.JavaElementAdapterFactory" 
	adaptableType="org.eclipse.jdt.core.IJavaElement">
      <adapter class="org.eclipse.core.resources.IFile">
      <adapter class="org.eclipse.ui.views.IPropertySource">
      <adapter class="org.eclipse.ui.model.IWorkbenchAdapter">
      ...
   </factory>
</extension>

This extension point specifies a factory that adapts IJavaElement to IFile, IPropertySource, etc. Of course, for backwards compatibility we will continue to support adapters registered manually that do no have associated markup.