/**
   * @see
   *     org.eclipse.core.commands.AbstractHandler#execute(org.eclipse.core.commands.ExecutionEvent)
   */
  public Object execute(ExecutionEvent event) throws ExecutionException {
    toSelect = new ArrayList<EObject>();
    IEditorPart editor = RequirementUtils.getCurrentEditor();
    IEditorServices services = SupportingEditorsManager.getInstance().getServices(editor);
    CurrentPage page = RequirementHelper.INSTANCE.getCurrentPage();

    if (services != null
        && ((EvaluationContext) event.getApplicationContext()).getDefaultVariable()
            instanceof List<?>) {
      EditingDomain editingDomain = services.getEditingDomain(editor);
      // Get the current selection
      List<?> elements =
          ((List<?>) ((EvaluationContext) event.getApplicationContext()).getDefaultVariable());
      CompoundCommand compoundCmd =
          new CompoundCommand(Messages.getString("AddAttributeHandler.1")); // $NON-NLS-1$
      for (Object currObject : elements) {
        EObject parent = null;
        if (currObject instanceof Attribute) {
          parent = ((Attribute) currObject).eContainer();
          int newIndex = calculateIndex(parent, (EObject) currObject);

          Attribute toDuplicate = null;
          if (currObject instanceof AttributeLink) {
            toDuplicate =
                RequirementHelper.INSTANCE.duplicateAttributeLink((AttributeLink) currObject);
          } else if (currObject instanceof ObjectAttribute) {
            toDuplicate =
                RequirementHelper.INSTANCE.duplicateObjectAttribute((ObjectAttribute) currObject);
          }
          if (parent != null && toDuplicate != null) {
            toSelect.add(toDuplicate);
            compoundCmd.appendIfCanExecute(
                AddCommand.create(
                    editingDomain,
                    parent,
                    RequirementPackage.eINSTANCE.getRequirement_Attribute(),
                    toDuplicate,
                    newIndex));
          }
        }
      }
      if (!compoundCmd.isEmpty() && compoundCmd.canExecute()) {
        editingDomain.getCommandStack().execute(compoundCmd);
        page.setSelection(new StructuredSelection(toSelect));
      }
    }
    return null;
  }
 /** Refreshes the current page viewer */
 private void refreshViewer() {
   CurrentPage page = RequirementHelper.INSTANCE.getCurrentPage();
   page.setSelection(new StructuredSelection(toCopy));
 }