public void SendFile(FileMessage fileMessage, string receiver)
 {
     if (ClientCallBacks.ContainsKey(receiver))
     {
         ClientCallBacks[receiver].ReceiverFile(fileMessage, receiver);
     }
     else
     {
         throw new FaultException(fileMessage.Sender + "Không online...");
     }
 }
 public void SendFile(FileMessage fileMessage, string receiver)
 {
     if (ClientCallBacks.ContainsKey(receiver))
         {
             ClientCallBacks[receiver].ReceiverFile(fileMessage, receiver);
         }
         else
         {
             throw new FaultException(fileMessage.Sender + "Không online...");
         }
 }