Enable/disable menu item in Eclipse plugin

Question

I've made a pop-up menu with one menu item, I want to enable it only when I do a right click on a tree item of a certain class type otherwise disable it.

How can I achieve this?

Answer 1

You can add a handler that uses activeWhen and associate it with that menu's command id.

Here is a handler that makes a command active only when the current selection is not empty, and the selection is an item that can be adapted to an object of type Widget:

<extension point="org.eclipse.ui.handlers">
  <handler class="com.myproject.handlers.ExportWidgetHandler"
           commandId="com.myproject.commands.exportWidget">
     <activeWhen>
        <with variable="selection">
           <iterate ifEmpty="false" operator="and">
              <adapt type="com.myproject.objects.Widget"/>
           </iterate>
        </with>
     </activeWhen>
  </handler>
</extension>