our example by installing an activity policy filter on \p rootNode and \p nodeA using the convenience functions of Qtilities::CoreGui::TreeNode. 

\code
rootNode->enableActivityControl(ObserverHints::CheckboxActivityDisplay,ObserverHints::CheckboxTriggered);
nodeA->enableActivityControl(ObserverHints::CheckboxActivityDisplay,ObserverHints::CheckboxTriggered);
\endcode

After adding the activity filter, the observer widget will look like this:

\image html observer_widget_doc_tree_view_activity_control.jpg "