public void CloseMessageBoxTip()
{
if (null != _messageBoxTip && _messageBoxTip.IsLoaded)
{
// only keep the last prompt message to show
log.InfoFormat("Prompt message arrived, but previous message is still displayed, close it. Message -- {0}", _messageTipExtraInfo);
_messageBoxTip.Close();
_messageBoxTip = null;
}
}