我正在开发一个反应原生应用程序与Firebase身份验证。但是当我成功登录时，导航显示出一些问题，比如，未定义不是一个对象（评估this.props.navigation）。我尝试了很多方法，但都没用。伙计们，请帮帮我。

      import React from "react";
      import {
        Text,
        View,
        Image,
        TouchableOpacity,
        AsyncStorage,
        TextInput
      } from "react-native";
      import { styles } from "./Css";
      import { KeyboardAvoidingView } from "react-native";
      import { RkTextInput, RkButton } from "react-native-ui-kitten";
      import { Actions } from "react-native-router-flux";
      import { Icon } from "react-native-elements";

      import * as firebase from "firebase";
      export default class Login extends React.Component {
        constructor(props) {
          super(props);

          this.state = {
            email: "",
            password: "",
            userId: "",
            errorMessage: null,
          };
        }
        componentDidMount() {
          this._loadInitialState().done();
        }
        _loadInitialState = async () => {
          var value = await AsyncStorage.getItem("user");

          if (value !== null) {
            this.props.navigation.navigate("NewHome")
          }
        };

        handleLogin = (email, password) => {
          if(this.state.email.length<1){
            alert("Enter an Email");
            return;
          }

          if (this.state.email.includes("@")==false){
              alert("Use an email as Username");
              return;
            }

          if(this.state.password.length<6){
            alert("please enter correct password")
            return;
          }

          //alert(firebase.auth().currentUser.uid)
          firebase.auth().signInWithEmailAndPassword(email, password).then(function(user){
            if(user){
              this.props.navigation.navigate("NewHome"), //problem
              //--------------------------Async Test--------------------------
              AsyncStorage.setItem("user", firebase.auth().currentUser.uid)
              //--------------------------------------------------------------
            }else{

            }
          }


            )
            .catch(function(error) {
              var errorCode = error.code;
              var errorMessage = error.message;

              if (errorCode === "auth/wrong-password") {
                alert("Wrong password.");
                return;
              } else {
                alert(errorMessage);
                return;
              }
              console.log(error);
            });
        };