geocodeAync 错误阻止 function 拍摄

Question

enter image description here ] 1 rybody I am building a location based component need to take the city name to pass it through a get request for API to be like this axios.get( /${cityName}/JSON );

in the component I am writing some times working well but most of the time is giving that error ( null is not an object (evaluating 'location.coords')] )

How to get over that and how to get the cityName alone using latitude and longitude or whatever any other method

import React, { useState, useEffect } from 'react';
import { Platform, Text, View, Button } from 'react-native';
import Constants from 'expo-constants';
import * as Location from 'expo-location';


export default function App() {
  const [location, setLocation] = useState(null);
  const [errorMsg, setErrorMsg] = useState(null);
  const [city, setCity] = useState('');

 const getLocation = async () => {
    let { status } = await Location.requestPermissionsAsync();
    if (status !== 'granted') {
      setErrorMsg('Permission to access location was denied');
    }

    let location = await Location.getCurrentPositionAsync({});
    setLocation(location);
    console.log(location);
  }

  const getCity = async () => {
      const place = await Location.reverseGeocodeAsync({
          latitude : location.coords.latitude,
          longitude : location.coords.longitude
      });
      setCity(place.city);
      console.log(city);
  }

    useEffect(() => {
        getLocation() , getCity();
    } , []);



  let text = 'Waiting..';
  if (errorMsg) {
    text = errorMsg;
  } else if (location) {
    text = JSON.stringify(location);
  }

  return (
    <View >
        <Text> </Text>
        <Button title = 'press' 
        onPress = {getCity}
        />
    </View>
  );
}

Answer 1

So, the issue is that you are calling getCity when the component is first redered here without having the location object:

useEffect(() => {
    getLocation() , getCity();
} , []);

Both functions are async, but that is not a guarantee that they will happen in that order. Moreover, what happens is that the functions run in parallel and that leads to your error.

You have multiple options here: - you can chain together multiple promises to ensure order of execution - you can remove the getCity call from the above useEffect and call it only after the getLocation call is done (do not allow the user to Interact before that)