class MyNavigator extends Application, implements INavigator
     {
         import com.adobe.portfolio.api.INavigator;
     
         public function set host(val:INavigatorHost):void
         {
             if(val)
                 {
                  NavigatorHostInstance.initialize(val);
     
                     //Other initialization...
             } 
                 else
                 {
                     NavigatorHostInstance.release();
                     
                     //Other cleanup code...
                 } 
         } 
     
     }