问react本机应用程序没有运行-启动屏幕显示

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import { registerRootComponent } from 'expo';

import App4 from './App4';

// registerRootComponent calls AppRegistry.registerComponent('main', () => App);
// It also ensures that whether you load the app in Expo Go or in a native build,
// the environment is set up appropriately
registerRootComponent(App4);

import React from 'react'
import List from './List.js'

const App = () => {
   return (
      <List />
   )
}
export default App

import React, { Component } from 'react'
import { Text, View, TouchableOpacity, StyleSheet, Image } from 'react-native'
   
class List extends Component {
   state = {
      products: []
   }

   componentDidMount() {
      this.GetAllProducts();
   }

   GetAllProducts() {
      //fetch("http://192.168.2.14:3000/getallproducts")
      fetch("https://categoriesexpress444.herokuapp.com/getallproducts")
         .then(res => res.json())
         .then(jsonresult => {
            this.setState({
                  products: jsonresult
            });
            console.log(this.state.products);
         });
   }

   getsrcPath(string) { // this function distinguishes between images in UserImages folder and images on Cloudinary
      var firstChar = string.charAt(0);
      if (firstChar == '~') { // image is in UserImages folder and item.picture path starts wih ~/UserImages/
         return string.substring(1, string.length);
      }
      else { // image is at Cloudinary and item.picture starts with http://
         return string;
      }
   }

   render() {
      return (
         <View>
            {
               this.state.products.map((item, index) => (
                  <TouchableOpacity
                     key = {item.id}
                     style = {styles.container}>
                     <Text style = {styles.text}>{item.productname}</Text>
                     <Text>{item.description}</Text>
                     <Text>€ {item.price}</Text>
                     <img src={this.getsrcPath(item.picture)} />
                     <Text style = {styles.text}>
                        {item.name}
                     </Text>
                  </TouchableOpacity>
               ))
            }
         </View>
      )
   }
}
export default List

const styles = StyleSheet.create ({
   container: {
      padding: 10,
      marginTop: 3,
      backgroundColor: '#ffffff',
      alignItems: 'center',
      cursor: 'none'
   },
   text: {
      color: '#4f603c'
   }
})