来自 API 调用的 React-Native 变量引发错误

Question

I'm really rusty with my react-native, haven't touched it in like 4 years.

I am trying to extract a cryptocurrency price from a publicly available API (as shown in the code below). i think I got the price but packing that value into something that's usable is proving to be difficult. What am i doing wrong? Either I haven't set up the const correctly or something else is going on.

import React, {Component, useState, useEffect} from 'react';
import {AppRegistry, StyleSheet, Text, View} from 'react-native';

const getPriceFromApi = () => {
  //GET request
  fetch('https://api.coingecko.com/api/v3/simple/price?ids=bone-shibaswap&vs_currencies=usd', {
    method: 'GET',
  })
    .then((response) => response.json())
      //If response is json then in success
    .then((responseJson) => {
      //Success
      return responseJson;
    })
}

const App = () => {
  const [price, setPrice] = useState([]);

  useEffect(() => {
    const fetchPrice = async () => {
      const data = await getPriceFromApi();
      setPrice(data);
      // this should produce ONE value and one value only. 
      // however it’s throwing an error, grrrrr. 
    }
  }, [getPriceFromApi])

  return ();

type Props = {};
export default class MyApp extends Component<Props> {
  render() {
    return (
      <View style={styles.container}>
      <Text style={styles.bone}>
          🍖
        </Text>
        <Text style={styles.welcome}>
          you have > 120.00
        </Text>
        <Text style={styles.instructions}>
          the value of bone is: 
        </Text>
      </View>
    );
  }
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    justifyContent: 'center',
    alignItems: 'center',
    backgroundColor: '#2A2734',
  },
  bone: {
    fontSize: 64,
    textAlign: 'center',
    margin: 10,
    color: 'red'
  },
  welcome: {
    fontSize: 20,
    textAlign: 'center',
    margin: 10,
    color: 'white'
  },
  instructions: {
    textAlign: 'center',
    color: '#B0B0B0',
    marginBottom: 5,
  },
});

// You must register the main component
// with the same name as the project
AppRegistry.registerComponent(
  'bone-price', () => MyApp
);

Answer 1

If you are writing a another function for fetching data from API, you may forget to return the value by fetch. It will always return undefined.

You should modify the function getPriceFromApi().

const getPriceFromApi = () => {
  //This return is for function - getPriceFromApi()
  return fetch('https://api.coingecko.com/api/v3/simple/price?ids=bone-shibaswap&vs_currencies=usd', {
    method: 'GET',
  })
    .then((response) => response.json())
    .then((responseJson) => {
      //This return is for function - fetch()
      return responseJson;
    })
}