The OnBase widget registers an Activate OnBase and a Deactivate OnBase command when it initializes in the Geocortex Viewer. Following either of these commands, the OnBase widget publishes either an OnBaseActivatedEvent or an OnBaseDeactivatedEvent in case you need to listen to when this widget becomes activated or deactivated.
In addition, it is possible to configure the widget by following steps previously mentioned to enable a SendToOnBase command, which takes results from valid Geocortex Viewer application operations and sends them to the OnBase widget for results. When the command fires, it publishes a SendToOnBase Event.
See your Geocortex documentation on commands and events for more information.