javascript - 指南针使用expo记录磁力计的值？

Question

我想制作一个应用程序，使指南针和指南针应该随着磁力计方向的变化而变化。下面附加的代码显示了一个奇怪的错误。虽然我已经运行 npm install react-timer-mixin 来解决问题。通过在 Expo 上运行此代码，它会显示类似

的错误

Super expression must either be a null or a function.

import React, {Components} from 'react';
import {Image, ImageBackground, View, Text, StyleSheet} from 'react-native';
import Expo from 'expo';

export default class App extends Components{
  state={
    isReady: false,
    v: null,
  };

  _setMagnetometerAsync = async() =>{
    Expo.Magnetometer.addListener((v)=>{
      this.setState({v});
    });
  }
  componentDidMount() {
    this._setupMagnetometerAsync();
  }
  render(){
    return(
      <View style = {styles.container}>
      <Text>{JSON.stringify(this.state.v)}</Text>
      <ImageBackground
      source = {require('./compassFace.png')}
      style = {{
        height: 320,
        width: 320,
        paddingTop:Expo.Constants.statusBarHeight,
        alignItems: 'center',
        justifyContents: 'center',
      }}>
        <Image
        source = {require('./CompassNeedle.png')}
        style={{
          height: 420,
          width: 420,
          opacity: 0.65,
        }}
        />
      </ImageBackground>
      </View>
    );
  }
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    justifyContent: 'center',
    alignItems: 'center',
    backgroundColor: '#ecf0f1',
  },
  paragraph:{
    margin: 24,
    fontSize: 18,
    fontWeight: 'bold',
    textAlign: 'center',
    color: '#34495e',
  },
});

Answer 1

一些修复:1.

import React, {Components} from 'react';

到

import * as React from 'react';

2.

 componentDidMount(){
        this._setupMagnetometerAsync();
      }

到

 componentDidMount(){
        this._setMagnetometerAsync();
      }

3.

 export default class App extends Components{

至

export default class App extends React.Component{