React-Native: Go back on android hardware back but

问题:

I am trying to add going back on webview when the android backbutton was pressed and I still couldn't manage to make it work.

This is my code:

<WebView
    ref={WEBVIEW_REF}
    source={source}
    domStorageEnabled={true}
    onNavigationStateChange={this.onNavigationStateChange}
/>

componentDidMount() {
    BackAndroid.addEventListener('hardwareBackPress', function() {
        if(this.state.backButtonEnabled) {
            this.refs[WEBVIEW_REF].goBack();
            return true;
        }
    });
};

onNavigationStateChange = (navState) => {
    this.setState({
        backButtonEnabled: navState.canGoBack,
    });
};

With the code above I'm getting the error undefined is not an object this.state.backButtonEnabled (which is set in the state).

Than I just wanted to see if the goBack works so I removed the if statement and than I was getting the error undefined is not an object this.refs[WEBVIEW_REF].

What is the best solution for this?

回答1:

class MyComponent extends Component {
    state = {};
    componentDidMount(){
         BackHandler.addEventListener('hardwareBackPress', this.backHandler);
    }
    componentWillUnmount(){
         BackHandler.removeEventListener('hardwareBackPress', this.backHandler);
    }
    backHandler = () => {
        if(this.state.backButtonEnabled) {
            this.refs[WEBVIEW_REF].goBack();
            return true;
        }
    }
}

1) Bind your handler 2) Do not forget to removeListener on unmount.

回答2:

Wanted to add a full example in case it helps anyone:

import React, { Component } from 'react';
import {
  BackHandler,
  Platform,
  WebView,
} from 'react-native';

class ExampleWebView extends Component {
  webView = {
    canGoBack: false,
    ref: null,
  }

  onAndroidBackPress = () => {
    if (this.webView.canGoBack && this.webView.ref) {
      this.webView.ref.goBack();
      return true;
    }
    return false;
  }

  componentWillMount() {
    if (Platform.OS === 'android') {
      BackHandler.addEventListener('hardwareBackPress', this.onAndroidBackPress);
    }
  }

  componentWillUnmount() {
    if (Platform.OS === 'android') {
      BackHandler.removeEventListener('hardwareBackPress');
    }
  }

  render() {
    return (
      <WebView
        source={{ uri: "https://www.google.com" }}
        ref={(webView) => { this.webView.ref = webView; }}
        onNavigationStateChange={(navState) => { this.webView.canGoBack = navState.canGoBack; }}
      />
    );
  }
}

回答3:

This might help someone as the above solutions didn't solve my problem....

import React, { Component } from 'react';
import {
  BackHandler,
  WebView,
} from 'react-native';

export default class App extends Component {

constructor(props) {
    super(props);
    this.WEBVIEW_REF = React.createRef();
}

componentDidMount() {
    BackHandler.addEventListener('hardwareBackPress', this.handleBackButton);
}

componentWillUnmount() {
  BackHandler.removeEventListener('hardwareBackPress', this.handleBackButton);
}

handleBackButton = ()=>{
   this.WEBVIEW_REF.current.goBack();
   return true;
}

onNavigationStateChange(navState) {
  this.setState({
    canGoBack: navState.canGoBack
  });
}

render(){
   return (
    <WebView
        source={{ uri: "https://www.cbt.ng" }}
        ref={this.WEBVIEW_REF}
        onNavigationStateChange={this.onNavigationStateChange.bind(this)}
     />
    )

 }
}

回答4:

Here's a solution with Typescript and useRef and useEffect hooks.

I didn't use canGoBack, but it seems to work regardless.

import React, { useEffect, useRef } from 'react';
import { BackHandler } from 'react-native';
import WebView from 'react-native-webview';

const WebViewWrapper = (): JSX.Element => {
  const webview = useRef<WebView>(null);
  const onAndroidBackPress = (): boolean => {
    if (webview.current) {
      webview.current.goBack();
      return true; // prevent default behavior (exit app)
    }
    return false;
  };
  useEffect((): (() => void) => {
    BackHandler.addEventListener('hardwareBackPress', onAndroidBackPress);
    return (): void => {
      BackHandler.removeEventListener('hardwareBackPress', onAndroidBackPress);
    };
  }, []); // Never re-run this effect
  return (
    <WebView
      source={{ uri: 'https://stackoverflow.com' }}
      ref={webview}
    />
  )
}

回答5:

In case of webview in react native, app exit when pressing the back button of mobile by default. If you want to go the previous page when pressing the back button then you need to implement the "goback" function of react-native webview.

You can see the Step 5 : Handle Mobile Back Button section of this article.