在 reactnative 中设置动态 'initialRouteName'

问题很简单，我知道同一个问题有很多答案，但我有不同的设置我自己的App.js个文件，我try 了几乎所有，但没有成功.

所以我的App.js看起来像这样

import React, { Component } from 'react';
import {
  Platform,
  StyleSheet,
  Text,
  View,
  StatusBar
} from 'react-native';
import { createStackNavigator  } from 'react-navigation';
import { Header, Button, Spinner } from './src/components/comman';
import SplashScreen from 'react-native-splash-screen';
import LoginForm from './src/components/LoginForm';
import SignupForm from './src/components/SignupForm';
import Home from './src/components/Home';
import ForgetPassword from './src/components/ForgetPassword';


import { YellowBox } from 'react-native';
YellowBox.ignoreWarnings(['Warning: isMounted(...) is deprecated', 'Module RCTImageLoader']);
const App = createStackNavigator ({
  Login: { screen: LoginForm },
  Home: { screen: Home },
  Signup: { screen: SignupForm },
  ForgetPassword: { screen : ForgetPassword },
  },
  { 
  initialRouteName: 'Login',
  });

export default App;

现在我将登录状态存储在我的LoginForm.js中的AsyncStorage中，如下所示

.
.
AsyncStorage.setItem('isLoggedIn', 'true').then((a) => {
    this.onLoginSuccess(responseData.user_id);
});
.
.

现在我想根据本地存储元素设置initialRouteName.

简单但不知道如何在my App.js中使用它

请帮忙:)