private Activity HandleSystemMessage(Activity message) { if (message.Type == ActivityTypes.DeleteUserData) { // Implement user deletion here // If we handle user deletion, return a real message } else if (message.Type == ActivityTypes.ConversationUpdate) { // Handle conversation state changes, like members being added and removed // Use Activity.MembersAdded and Activity.MembersRemoved and Activity.Action for info // Not available in all channels foreach (var x in message.MembersAdded) { ConversationState.AddUser(x.Name); } } else if (message.Type == ActivityTypes.ContactRelationUpdate) { // Handle add/remove from contact lists // Activity.From + Activity.Action represent what happened } else if (message.Type == ActivityTypes.Typing) { // Handle knowing tha the user is typing } else if (message.Type == ActivityTypes.Ping) { } return(null); }