问JSQMessagesViewController 7.3.4 + Firebase (3.7.1) observeMessages无法访问FIRDataSnapshot

EN

private func observeMessages() {
        let messagesQuery = messageRef.queryLimited(toLast: 25)

        messagesQuery.observe(.childAdded) { (snapshot: FIRDataSnapshot!) in

            let id = (snapshot.value as! NSDictionary)["name"] as! String
            let text = (snapshot.value as! NSDictionary)["text"] as! String
            //let photoUrl = (snapshot.value as! NSDictionary)["photoUrl"] as! String

            self.addMessage(id: id, text: text)
            self.finishReceivingMessage()
        }
    }