我是 React Native 新手，正在尝试创建我的第一个应用程序。所以我有一个问题：

我有 2 个屏幕（使用 react-navigation）。第一个屏幕上会渲染带有旋转器的应用程序徽标（来自 native-base）并同时获取到服务器。并且我只需要在获取结束并处理响应时导航到另一个屏幕。请帮我找出我的错误！

index.ios.js

import React, { Component } from 'react';
import {
  AppRegistry,
  StyleSheet,
  Text,
  View,
  TextInput,TouchableHighlight
} from 'react-native';
import { StackNavigator } from 'react-navigation';
import LoadingScreen from './src/screens/LoadingScreen.js';
import MainContainer from './src/screens/MainContainer.js';

export default class Calculator2 extends Component {
  render() {
    return (
      <LoadingScreen/>
    );
  }
}
const AppNavigator = StackNavigator({
  Loading: {
    screen: LoadingScreen
   },
  Main: {
    screen: MainContainer
  }
});

AppRegistry.registerComponent('Calculator2', () => Calculator2);

LoadingScreen.js：

import React, { Component } from 'react';
import {
  AsyncStorage,
  AppRegistry,NetInfo,
  Text,Image,View
} from 'react-native';
import { StackNavigator } from 'react-navigation';
import AppNavigator from '../../index.ios.js';
import { Container, Header, Content, Spinner } from 'native-base';

export default class LoadingScreen extends Component {
  static navigationOptions = {
    title: 'Loading',
  };
  constructor(props){
   super(props);

  }
  componentDidMount(){
    const {navigate} = this.props.navigation;
    fetch('url').then( (response) => {navigate('Main')});
  }
  render() {
    return(
          <View>
            App logo with spinner
          </View>
   );
  }
}

MainContainer.js

import React, { Component } from 'react';
import {
  AppRegistry,Alert,NetInfo,
  StyleSheet,
  Text,
  View,ActivityIndicator,
  TextInput,TouchableHighlight
} from 'react-native';

import { StackNavigator } from 'react-navigation';
import AppNavigator from '../../index.ios.js';

export default class MainContainer extends Component {
  static navigationOptions = {
    title: 'Main',
  };

  render() {
    return (
      <View  style={{flexDirection: 'column'}}>
         ...
      </View>
    );
  }
}

而我得到的只是在 LoadingScreen.componentDidMount 处出现的错误“无法读取未定义的属性‘navigate’”

UPD 实际上我的获取应该是一个获取响应并处理它的函数，它应该等到处理完成：

async function getData(){
    var response = await fetch('url', {
      method: 'GET'
    });
    storage = await response.json(); // storage for response
    regions = Object.keys(storage); // an array of regions names
    console.log(storage, Object.keys(storage));
  };