private void UnsubscribeClearCacheCallback()
 {
     if (_streamEventDispatcher != null)
     {
         _streamEventDispatcher.RemoveStreamCallback(ClearCache);
         _streamEventDispatcher = null;
     }
 }
 private void ClearCacheOnStreamCallback(StreamContext context)
 {
     if (_streamEventDispatcher != context.dispatcher)
     {
         UnsubscribeClearCacheCallback(); // unsub from previous dispatcher
     }
     _streamEventDispatcher = context.dispatcher;
     _streamEventDispatcher.AddStreamCallback(context.updateID, ClearCache);
 }