我想在訂閱塊中調用方法，但我得到“無法讀取未定義的屬性‘showMessageFromSocket’”。如何調用 showMessageFromSocket 方法？從角度來看這是可能的。export default class ConnectedChatroom extends Component<  ConnectedChatroomProps,  ConnectedChatroomState> {  wsObj: CompatClient;  constructor(props: Props, context: *) {    super(props, context);    this.configureSocketChannel('dassfa')  }  showMessageFromSocket(message)  {    console.log(message);    //do something  }  configureSocketChannel(senderId: string) {    let ws = Stomp.client("ws://localhost:8080/chat");    ws.connect({}, function (frame) {      ws.subscribe("/topic/messages", function (message) {        this.showMessageFromSocket(message);      });    }, function (error) {      console.log("STOMP error " + error);    });    this.wsObj = ws;  }