为什么 getCurrentPositionAsync 从不 returns 任何东西？

Question

感谢您访问此 post。我在使用 React Native 获取用户位置时遇到问题。

我找了好久，也看了别人关于这个功能的post。看来这个功能有几个问题。

而且 React Native Expo 文档似乎已过时。 https://docs.expo.dev/versions/latest/sdk/location/ 我在使用部分使用此处的代码。

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

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

  useEffect(async () => {
    (async () => {
      let { status } = await Location.requestForegroundPermissionsAsync();
      console.log(status);
      if (status !== 'granted') {
        console.log("denied")
        setErrorMsg('Permission to access location was denied');
        return;
      }

      console.log("status", status); // <=== always says "granted"

      let location = await Location.getCurrentPositionAsync({
        accuracy: Location.Accuracy.Highest,
        maximumAge: 10000,
        timeout: 5000
      });
      console.log({ location }) // <== never reach here.
      setLocation(location);
      setErrorMsg('No ERROR');
    })();
  }, []);

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

  return (
    <View>
      <Text>{text}</Text>
    </View>
  );
}

我看到 post 中的一个说我必须将 accuracy, maximumAge 的参数传递给 getCurrentPositionAsync，而不是 expo 文档中提供的 {} empty object . 但还是不行。由于 getCurrentPositionAsync 挂起，屏幕继续显示 waiting...。

当然，我相信 android 模拟器设置正确，因为我确实看到了状态日志，它说 "granted"。

非常感谢您的帮助和阅读我的post。

    "expo": "~43.0.2",
    "expo-location": "~13.0.4",
    "expo-status-bar": "~1.1.0",
    "react": "17.0.1",
    "react-dom": "17.0.1",
    "react-native": "0.64.3",
    "react-native-web": "0.17.1"

Answer 1

您不能将 async 与 useEffect 一起使用，因此不能等待。

你试过相反的方法吗？

const [position, setPosition] = useState(false)
// useEffect  
  Location.getCurrentPositionAsync({
    accuracy: Location.Accuracy.Highest,
    maximumAge: 10000,
    timeout: 5000
  })
  .then(res => setPosition(res))
  .catch(e => console.log(e)

我也有更多机会没有非脂肪箭头 IIFE，你应该试试

(function () {
      let { status } = await Location.requestForegroundPermissionsAsync();
      console.log(status);
      if (status !== 'granted') {
        console.log("denied")
        setErrorMsg('Permission to access location was denied');
        return;
      }

      console.log("status", status); // <=== always says "granted"

      let location = await Location.getCurrentPositionAsync({
        accuracy: Location.Accuracy.Highest,
        maximumAge: 10000,
        timeout: 5000
      });
      console.log({ location }) // <== never reach here.
      setLocation(location);
      setErrorMsg('No ERROR');
})();

为什么 getCurrentPositionAsync 从不 returns 任何东西？

Why does getCurrentPositionAsync never returns anything?

android

geolocation

react-native