public async Task RemoveScreenCastViewer(string agentName)
{
await Groups.RemoveFromGroupAsync(Context.ConnectionId, agentName);
_castManager.RemoveViewer(Context.ConnectionId);
if (!_castManager.IsViewerExists(agentName))
{
await Clients.Groups(AgentGroupPrefix + agentName).SendAsync("NoViewer");
_castManager.MessageCount += 1;
}
_castManager.MessageCount += 1;
}