App.js

import React, { Component } from 'react';
import {Text, View, StyleSheet, Alert, TouchableOpacity, Image} from 'react-native';
import { RNCamera } from 'react-native-camera';
  
  export default class BarcodeScan extends Component {
    constructor(props) {
      super(props);
    this.handleTourch = this.handleTourch.bind(this);
    this.state = {
      torchOn: false
    }
  }

  onBarCodeRead = (e) => {Alert.alert("Código de barras:" + "\n" + e.data, "Tipo do código de barras:" + "\n" + e.type);}
  
  render() {
    return (
      <View style={styles.container}>
        <RNCamera
          style={styles.preview}
          torchMode={this.state.torchOn ? RNCamera.Constants.FlashMode.torch : RNCamera.Constants.FlashMode.off}
          onBarCodeRead={this.onBarCodeRead}
          ref={cam => this.camera = cam}>

        <Text style={{backgroundColor: 'white'}}>BARCODE SCANNER</Text>

        </RNCamera>

        <View style={styles.bottomOverlay}>
          <TouchableOpacity onPress={() => this.handleTourch(this.state.torchOn)}>
            <Image style={styles.cameraIcon} />
            </TouchableOpacity>
        </View>
      </View>)
  }
  handleTourch(value) {
    if (value === true) {
    this.setState({ torchOn: false });
    } else {
    this.setState({ torchOn: true });}
    }
  }
  
  const styles = StyleSheet.create({
  container: {
  flex: 1,
  flexDirection: 'row',
  },preview: {
  flex: 1,
  justifyContent: 'flex-end',
  alignItems: 'center'
  },
  cameraIcon: {
  margin: 5,
  height: 40,
  width: 40
  },bottomOverlay: {
  position: "absolute",
  width: "100%",
  flex: 20,
  flexDirection: "row",
  justifyContent: "space-between"},});