Notifies this action delegate that the selection in the workbench has changed.
Implementers can use this opportunity to change the availability of the action or to modify other presentation properties.
When the selection changes, the action enablement state is updated based on the criteria specified in the plugin.xml file. Then the delegate is notified of the selection change regardless of whether the enablement criteria in the plugin.xml file is met.
@param action the action proxy that handles presentation portion of the action
@param selection the current selection, or
null
if thereis no selection.