Question

The Eclipse command framework allows you to create a generic command and handler. However, when you create an extension point that targets ‘copy’ the runtime complains:

<extension point="org.eclipse.ui.handlers">
 <handler class="example.Handler" commandId="org.eclipse.ui.edit.copy"/>
</extension>

!MESSAGE Conflicting handlers for org.eclipse.ui.edit.copy: {org.eclipse.ui.internal.handlers.WidgetMethodHandler:copy} vs {example.Handler}

If you add an activeWhen clause, so that the special handler is only invoked when an object of a particular type is selected in a viewer, then you get an exception when you try and copy:

<extension point="org.eclipse.ui.handlers">
 <handler class="example.Handler" commandId="org.eclipse.ui.edit.copy">
     <activeWhen>
        <with
              variable="selection">
           <iterate
                 ifEmpty="false"
                 operator="or">
              <instanceof
                    value="sample.Class">
              </instanceof>
           </iterate>
        </with>
     </activeWhen>
   </handler>
</extension>

Caused by: org.eclipse.core.commands.NotHandledException: There is no handler to execute for command org.eclipse.ui.edit.copy

What’s the right way of using the commands framework to provide a specific copy operation for objects of a particular type?

Answer 1

Your activeWhen clause looks acceptable. What will matter is what selection you are going for. ex:

  <handler class="z.ex.cmd.handlers.LongCopyHandler"
        commandId="org.eclipse.ui.edit.copy">
     <activeWhen>
        <with variable="selection">
           <iterate ifEmpty="false"
                 operator="and">
              <adapt type="org.eclipse.core.resources.IMarker"/>
           </iterate>
        </with>
     </activeWhen>
  </handler>

I originally tried instanceof in my activeWhen expression to get access to the IMarkers in the markers view, but that didn’t work (the objects don’t implement IMarker). I had to adapt them to get my handler to work correctly. This would apply to .java files in the Package Explorer as well, they adapt to an IResource but they’re actually IJavaElements or something.