expo webview android backbutton

I’ve started a week ago expo to publish my site to App with webview.
And I made my App with the code below. But,
problem is…
When I press back-button of android, my app turns off.
I want to make that, when I click back-button of android, my webview go back the page that I read just before.

Can I get some help? Thanks. (My English is a little poor. Sorry.)

	import React, { Component } from 'react';
	import { StyleSheet, Text, View,WebView } from 'react-native';
	import { Button } from 'react-native';   

	export default class App extends Component {
		onNavigationStateChange = navState => {
		  if (navState.url.indexOf('https://www.google.com') === 0) {
			const regex = /#access_token=(.+)/;
			let accessToken = navState.url.match(regex)[1];

		render() {
			const url = 'https://nandallinda.com';
			return (
				<View style={{marginTop: 24, flex:1, backgroundColor: '#fff'}}>
						uri: url,
					style={{ flex: 1 }}

	const styles = StyleSheet.create({
		container: {
			flex: 1,
			backgroundColor: '#fff',
			alignItems: 'center',
			justifyContent: 'center'