ChartObjectsSelectionChangedEventArgs

 using cAlgo.API;
 namespace cAlgo
 {
     // This example shows how to use the Chart ChartObjectsSelectionChangedEventArgs
     // Draw an object, select it and unselect it
     [Indicator(IsOverlay = true, TimeZone = TimeZones.UTC, AccessRights = AccessRights.None)]
     public class ChartObjectsSelectionChangedEventArgsSample : Indicator
     {
         protected override void Initialize()
         {
             Chart.ObjectsSelectionChanged += Chart_ObjectsSelectionChanged;
         }
         private void Chart_ObjectsSelectionChanged(ChartObjectsSelectionChangedEventArgs obj)
         {
             Print("Added objects #: {0} | Removed Objects #: {1}", obj.ObjectsAddedToSelection.Count, obj.ObjectsRemovedFromSelection.Count);
         }
         public override void Calculate(int index)
         {
         }
     }
 }

 import clr
 clr.AddReference("cAlgo.API")
 from cAlgo.API import *
 class Test():    
     def initialize(self):
         api.Chart.ObjectsSelectionChanged += self.on_chart_objects_selection_changed
     def on_chart_objects_selection_changed(self, args):
         print(f"Added objects #: {args.ObjectsAddedToSelection.Count} | Removed Objects #: {args.ObjectsRemovedFromSelection.Count}")