使用 flutter webview 作为主页并按后退按钮关闭应用程序

问题描述 投票：0回答：9

我正在尝试使用 flutter 中的 webview 作为我的应用程序的主页。一切都加载得很好，但是点击后退按钮不会将我带到网络视图中的上一个网页，它只是退出应用程序。

import 'package:flutter/material.dart';
import 'package:webview_flutter/webview_flutter.dart';
import 'package:url_launcher/url_launcher.dart';

class _StudentPortalState extends State<StudentPortal>{

  _launchURL(url) async {

  if (await canLaunch(url)) {
    await launch(url);
  } else {
    throw 'Could not launch $url';
  }
}
  Widget build (BuildContext context){
    return Scaffold(
      body: WebView(
              javascriptMode: JavascriptMode.unrestricted,
              initialUrl: 'https://sites.google.com/ttmsa.org/ttmsa/home',

              navigationDelegate: (NavigationRequest request) {

                if(request.url.contains("intent:")) {

                  _launchURL('https://forms.gle/XfNbn1Ph9xFdUaKeA');
                  return NavigationDecision.prevent;
                }
                return NavigationDecision.navigate;
              },   
      ),

    );
  }
}`
flutter webview flutter-dependencies
9个回答
34
投票

使用 WillPopScope 包裹脚手架，当用户单击设备后退按钮时执行 WebView 控制器返回

onwillpop 代码片段

    @override
  Widget build(BuildContext context) {
    return WillPopScope(
      onWillPop: () => _exitApp(context),
      child: Scaffold(
        appBar: AppBar(
          title: const Text('Flutter WebView example'),
          // This drop down menu demonstrates that Flutter widgets can be shown over the web view.
          actions: <Widget>[
            NavigationControls(_controller.future),
            SampleMenu(_controller.future),
          ],
        ),

退出应用程序的代码片段

WebViewController controllerGlobal;

Future<bool> _exitApp(BuildContext context) async {
  if (await controllerGlobal.canGoBack()) {
    print("onwill goback");
    controllerGlobal.goBack();
    return Future.value(true);
  } else {
    Scaffold.of(context).showSnackBar(
      const SnackBar(content: Text("No back history item")),
    );
    return Future.value(false);
  }
}

完整代码

// Copyright 2018 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'dart:async';
import 'dart:convert';
import 'package:flutter/material.dart';
import 'package:webview_flutter/webview_flutter.dart';

void main() => runApp(MaterialApp(home: WebViewExample()));

const String kNavigationExamplePage = '''
<!DOCTYPE html><html>
<head><title>Navigation Delegate Example</title></head>
<body>
<p>
The navigation delegate is set to block navigation to the youtube website.
</p>
<ul>
<ul><a href="https://www.youtube.com/">https://www.youtube.com/</a></ul>
<ul><a href="https://www.google.com/">https://www.google.com/</a></ul>
<ul><a href="https://www.google.com/">https://nodejs.org/en</a></ul>
</ul>
</body>
</html>
''';

class WebViewExample extends StatefulWidget {
  @override
  _WebViewExampleState createState() => _WebViewExampleState();
}

WebViewController controllerGlobal;

Future<bool> _exitApp(BuildContext context) async {
  if (await controllerGlobal.canGoBack()) {
    print("onwill goback");
    controllerGlobal.goBack();
  } else {
    Scaffold.of(context).showSnackBar(
      const SnackBar(content: Text("No back history item")),
    );
    return Future.value(false);
  }
}

class _WebViewExampleState extends State<WebViewExample> {
  final Completer<WebViewController> _controller =
  Completer<WebViewController>();

  @override
  Widget build(BuildContext context) {
    return WillPopScope(
      onWillPop: () => _exitApp(context),
      child: Scaffold(
        appBar: AppBar(
          title: const Text('Flutter WebView example'),
          // This drop down menu demonstrates that Flutter widgets can be shown over the web view.
          actions: <Widget>[
            NavigationControls(_controller.future),
            SampleMenu(_controller.future),
          ],
        ),
        // We're using a Builder here so we have a context that is below the Scaffold
        // to allow calling Scaffold.of(context) so we can show a snackbar.
        body: Builder(builder: (BuildContext context) {
          return WebView(
            initialUrl: 'https://flutter.dev',
            javascriptMode: JavascriptMode.unrestricted,
            onWebViewCreated: (WebViewController webViewController) {
              _controller.complete(webViewController);
            },
            // TODO(iskakaushik): Remove this when collection literals makes it to stable.
            // ignore: prefer_collection_literals
            javascriptChannels: <JavascriptChannel>[
              _toasterJavascriptChannel(context),
            ].toSet(),
            navigationDelegate: (NavigationRequest request) {
              if (request.url.startsWith('https://www.youtube.com/')) {
                print('blocking navigation to $request}');
                return NavigationDecision.prevent;
              }
              if (request.url.startsWith('https://flutter.dev/docs')) {
                print('blocking navigation to $request}');
                return NavigationDecision.prevent;
              }
              print('allowing navigation to $request');
              return NavigationDecision.navigate;
            },
            onPageFinished: (String url) {
              print('Page finished loading: $url');
            },
          );
        }),
        floatingActionButton: favoriteButton(),
      ),
    );
  }

  JavascriptChannel _toasterJavascriptChannel(BuildContext context) {
    return JavascriptChannel(
        name: 'Toaster',
        onMessageReceived: (JavascriptMessage message) {
          Scaffold.of(context).showSnackBar(
            SnackBar(content: Text(message.message)),
          );
        });
  }

  Widget favoriteButton() {
    return FutureBuilder<WebViewController>(
        future: _controller.future,
        builder: (BuildContext context,
            AsyncSnapshot<WebViewController> controller) {
          if (controller.hasData) {
            return FloatingActionButton(
              onPressed: () async {
                final String url = await controller.data.currentUrl();
                Scaffold.of(context).showSnackBar(
                  SnackBar(content: Text('Favorited $url')),
                );
              },
              child: const Icon(Icons.favorite),
            );
          }
          return Container();
        });
  }
}

enum MenuOptions {
  showUserAgent,
  listCookies,
  clearCookies,
  addToCache,
  listCache,
  clearCache,
  navigationDelegate,
}

class SampleMenu extends StatelessWidget {
  SampleMenu(this.controller);

  final Future<WebViewController> controller;
  final CookieManager cookieManager = CookieManager();

  @override
  Widget build(BuildContext context) {
    return FutureBuilder<WebViewController>(
      future: controller,
      builder:
          (BuildContext context, AsyncSnapshot<WebViewController> controller) {
        return PopupMenuButton<MenuOptions>(
          onSelected: (MenuOptions value) {
            switch (value) {
              case MenuOptions.showUserAgent:
                _onShowUserAgent(controller.data, context);
                break;
              case MenuOptions.listCookies:
                _onListCookies(controller.data, context);
                break;
              case MenuOptions.clearCookies:
                _onClearCookies(context);
                break;
              case MenuOptions.addToCache:
                _onAddToCache(controller.data, context);
                break;
              case MenuOptions.listCache:
                _onListCache(controller.data, context);
                break;
              case MenuOptions.clearCache:
                _onClearCache(controller.data, context);
                break;
              case MenuOptions.navigationDelegate:
                _onNavigationDelegateExample(controller.data, context);
                break;
            }
          },
          itemBuilder: (BuildContext context) => <PopupMenuItem<MenuOptions>>[
            PopupMenuItem<MenuOptions>(
              value: MenuOptions.showUserAgent,
              child: const Text('Show user agent'),
              enabled: controller.hasData,
            ),
            const PopupMenuItem<MenuOptions>(
              value: MenuOptions.listCookies,
              child: Text('List cookies'),
            ),
            const PopupMenuItem<MenuOptions>(
              value: MenuOptions.clearCookies,
              child: Text('Clear cookies'),
            ),
            const PopupMenuItem<MenuOptions>(
              value: MenuOptions.addToCache,
              child: Text('Add to cache'),
            ),
            const PopupMenuItem<MenuOptions>(
              value: MenuOptions.listCache,
              child: Text('List cache'),
            ),
            const PopupMenuItem<MenuOptions>(
              value: MenuOptions.clearCache,
              child: Text('Clear cache'),
            ),
            const PopupMenuItem<MenuOptions>(
              value: MenuOptions.navigationDelegate,
              child: Text('Navigation Delegate example'),
            ),
          ],
        );
      },
    );
  }

  void _onShowUserAgent(
      WebViewController controller, BuildContext context) async {
    // Send a message with the user agent string to the Toaster JavaScript channel we registered
    // with the WebView.
    controller.evaluateJavascript(
        'Toaster.postMessage("User Agent: " + navigator.userAgent);');
  }

  void _onListCookies(
      WebViewController controller, BuildContext context) async {
    final String cookies =
    await controller.evaluateJavascript('document.cookie');
    Scaffold.of(context).showSnackBar(SnackBar(
      content: Column(
        mainAxisAlignment: MainAxisAlignment.end,
        mainAxisSize: MainAxisSize.min,
        children: <Widget>[
          const Text('Cookies:'),
          _getCookieList(cookies),
        ],
      ),
    ));
  }

  void _onAddToCache(WebViewController controller, BuildContext context) async {
    await controller.evaluateJavascript(
        'caches.open("test_caches_entry"); localStorage["test_localStorage"] = "dummy_entry";');
    Scaffold.of(context).showSnackBar(const SnackBar(
      content: Text('Added a test entry to cache.'),
    ));
  }

  void _onListCache(WebViewController controller, BuildContext context) async {
    await controller.evaluateJavascript('caches.keys()'
        '.then((cacheKeys) => JSON.stringify({"cacheKeys" : cacheKeys, "localStorage" : localStorage}))'
        '.then((caches) => Toaster.postMessage(caches))');
  }

  void _onClearCache(WebViewController controller, BuildContext context) async {
    await controller.clearCache();
    Scaffold.of(context).showSnackBar(const SnackBar(
      content: Text("Cache cleared."),
    ));
  }

  void _onClearCookies(BuildContext context) async {
    final bool hadCookies = await cookieManager.clearCookies();
    String message = 'There were cookies. Now, they are gone!';
    if (!hadCookies) {
      message = 'There are no cookies.';
    }
    Scaffold.of(context).showSnackBar(SnackBar(
      content: Text(message),
    ));
  }

  void _onNavigationDelegateExample(
      WebViewController controller, BuildContext context) async {
    final String contentBase64 =
    base64Encode(const Utf8Encoder().convert(kNavigationExamplePage));
    controller.loadUrl('data:text/html;base64,$contentBase64');
  }

  Widget _getCookieList(String cookies) {
    if (cookies == null || cookies == '""') {
      return Container();
    }
    final List<String> cookieList = cookies.split(';');
    final Iterable<Text> cookieWidgets =
    cookieList.map((String cookie) => Text(cookie));
    return Column(
      mainAxisAlignment: MainAxisAlignment.end,
      mainAxisSize: MainAxisSize.min,
      children: cookieWidgets.toList(),
    );
  }
}



class NavigationControls extends StatelessWidget {
  const NavigationControls(this._webViewControllerFuture)
      : assert(_webViewControllerFuture != null);

  final Future<WebViewController> _webViewControllerFuture;

  @override
  Widget build(BuildContext context) {
    return FutureBuilder<WebViewController>(
      future: _webViewControllerFuture,
      builder:
          (BuildContext context, AsyncSnapshot<WebViewController> snapshot) {
        final bool webViewReady =
            snapshot.connectionState == ConnectionState.done;
        final WebViewController controller = snapshot.data;
        controllerGlobal = controller;

        return Row(
          children: <Widget>[
            IconButton(
              icon: const Icon(Icons.arrow_back_ios),
              onPressed: !webViewReady
                  ? null
                  : () async {
                if (await controller.canGoBack()) {
                  controller.goBack();
                } else {
                  Scaffold.of(context).showSnackBar(
                    const SnackBar(content: Text("No back history item")),
                  );
                  return;
                }
              },
            ),
            IconButton(
              icon: const Icon(Icons.arrow_forward_ios),
              onPressed: !webViewReady
                  ? null
                  : () async {
                if (await controller.canGoForward()) {
                  controller.goForward();
                } else {
                  Scaffold.of(context).showSnackBar(
                    const SnackBar(
                        content: Text("No forward history item")),
                  );
                  return;
                }
              },
            ),
            IconButton(
              icon: const Icon(Icons.replay),
              onPressed: !webViewReady
                  ? null
                  : () {
                controller.reload();
              },
            ),
          ],
        );
      },
    );
  }
}

工作演示。我点击桌面页面，然后按设备后退按钮，您可以看到信息显示“onwill goback”。然后返回上一页

14
投票

完美运行的代码

import 'dart:async';
import 'dart:io';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:webview_flutter/webview_flutter.dart';

class Homepage extends StatefulWidget {
  @override
  HomepageState createState() => HomepageState();
}

class HomepageState extends State<Homepage> {
  WebViewController _controller;

  final Completer<WebViewController> _controllerCompleter =
      Completer<WebViewController>();

  @override
  void initState() {
    super.initState();
    // Enable hybrid composition.
    if (Platform.isAndroid) WebView.platform = SurfaceAndroidWebView();
  }

  @override
  Widget build(BuildContext context) {
    return WillPopScope(
      onWillPop: () => _goBack(context),
      child: WebView(
        initialUrl: 'https://google.com',
        javascriptMode: JavascriptMode.unrestricted,
        onWebViewCreated: (WebViewController webViewController) {
          _controllerCompleter.future.then((value) => _controller = value);
          _controllerCompleter.complete(webViewController);
        },
      ),
    );
  }

  Future<bool> _goBack(BuildContext context) async {
    if (await _controller.canGoBack()) {
      _controller.goBack();
      return Future.value(false);
    } else {
      showDialog(
          context: context,
          builder: (context) => AlertDialog(
                title: Text('Do you want to exit'),
                actions: <Widget>[
                  FlatButton(
                    onPressed: () {
                      Navigator.of(context).pop();
                    },
                    child: Text('No'),
                  ),
                  FlatButton(
                    onPressed: () {
                      SystemNavigator.pop();
                    },
                    child: Text('Yes'),
                  ),
                ],
              ));
      return Future.value(true);
    }
  }
}
7
投票

你必须控制WillPopScope组件中的逻辑：

import 'package:flutter/material.dart';
import 'package:webview_flutter/webview_flutter.dart';
import 'dart:async';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Home', url: 'https://flutter.dev/'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title, this.url});

  final String title;
  final String url;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  WebViewController _controller;

  final Completer<WebViewController> _controllerCompleter =
      Completer<WebViewController>();
  //Make sure this function return Future<bool> otherwise you will get an error
  Future<bool> _onWillPop(BuildContext context) async {
    if (await _controller.canGoBack()) {
      _controller.goBack();
      return Future.value(false);
    } else {
      return Future.value(true);
    }
  }

@override
  Widget build(BuildContext context) {
    return WillPopScope(
      onWillPop: () => _onWillPop(context),
      child: Scaffold(
        appBar: AppBar(
          title: Text(widget.title),
        ),
        body: SafeArea(
            child: WebView(
          key: UniqueKey(),
          onWebViewCreated: (WebViewController webViewController) {
            _controllerCompleter.future.then((value) => _controller = value);
            _controllerCompleter.complete(webViewController);
          },
          javascriptMode: JavascriptMode.unrestricted,
          initialUrl: widget.url,
        )),
      ),
    );
  }
}
3
投票

将 

WillPopScope
包裹在 Webview 小部件上，并使用 
canGoBack()
方法检查是否可以返回网页，如果可以，请使用 Webview 控制器中的 
goBack()
方法转到上一个网页。

class TheScreen extends StatelessWidget{

WebViewController? _controller;


Widget build(BuildContext context){
return WillPopScope(
      onWillPop: () async {
    bool? goBack = _controller?.canGoBack();
    if(goBack != true) return true;
    else {
        _controller.goBack();
        return false;
    }
},
child: WebView(
    initialUrl: "www.flutter.com",
    onWebViewCreated: (controller)=> _controller = controller),
}
}


}
2
投票

这是必须更好的答案（100％工作）-

  // Use any webview plugin
  // WebView _controller;

  Future<void> _handleBack(context) async {
    var status = await _controller.canGoBack();
    if (status) {
      _controller.goBack();
    } else {
      showDialog(
          context: context,
          builder: (context) => AlertDialog(
                title: Text('Do you want to exit'),
                actions: <Widget>[
                  FlatButton(
                    onPressed: () {
                      Navigator.of(context).pop();
                    },
                    child: Text('No'),
                  ),
                  FlatButton(
                    onPressed: () {
                      SystemNavigator.pop();
                    },
                    child: Text('Yes'),
                  ),
                ],
              ));
    }
  }

这里正在调用WillPopScope

  @override
  Widget build(BuildContext context) {
    return WillPopScope(
            onWillPop: () => _handleBack(context),
            child: SafeArea(
              top: true,
              child: Scaffold(......)))
2
投票

我改变后，chunhunghan的答案对我有用

return Future.value(true);

在 _exitApp() 的 if 块中

return Future.value(false);

如果为 true，网络视图将返回到上一个站点，在此之后 “默认设备后退按钮处理程序”（我不知道它的确切命名方式）关闭了应用程序。但是如果设置为 false，则打开 goBack 站点后应用程序不会关闭。

我将此作为额外答案发布，因为我的声誉太低，无法对答案发表评论。但我花了几个小时来找出这一点，并希望这些信息对其他人和我一样有帮助。

0
投票

onbackpressed Webview 代码

处理后退按钮的未来

    WebViewController controllerGlobal;

Future<bool> browserBack(BuildContext context) async{
  print('activated');
 if (await controllerGlobal.canGoBack()) {
    Scaffold.of(context).showSnackBar(
      const SnackBar(content: Text("Munching....")),
    );
    print("onwill goback");
    controllerGlobal.goBack();
  }
 else {
    SystemChannels.platform.invokeMethod('SystemNavigator.pop');
 return Future.value(false);
  }
}

WillPopScope 小部件

Widget build(BuildContext context) {


    return WillPopScope(
      onWillPop: ()=> browserBack(context),
      child:Scaffold(

      body: Builder(builder: (BuildContext context){
          return WebView(
            initialUrl: 'https://flutter.dev/docs/deployment/android',
            javascriptMode: JavascriptMode.unrestricted,
            onWebViewCreated: (WebViewController webViewController) {
            //  _controller.complete(webViewController);
              controllerGlobal = webViewController;
            },
          );
      },),

      ),
    );
0
投票

我发现了一种非常酷的前进和后退方式，既简单又实用。

这将由 appbar 完成。

appBar: AppBar(
        backgroundColor: Colors.red[900],
          actions: <Widget>[
            ElevatedButton(onPressed: (){
              print("Voltando");
              controller.goBack();
            },
                  style: ElevatedButton.styleFrom(
                  backgroundColor: Colors.red[900],
                ),
                child: Image.network('https://raw.githubusercontent.com/HeroRickyGAMES/Projeto-CPJ-Consulta-Juridica-de-Processos/master/src/voltar.png')
            ),
            ElevatedButton(onPressed: (){
              print("Indo pra frente");
              controller.goForward();
            },
              style: ElevatedButton.styleFrom(
              backgroundColor: Colors.red[900],
            ),
                child: Image.network('https://raw.githubusercontent.com/HeroRickyGAMES/Projeto-CPJ-Consulta-Juridica-de-Processos/master/src/irprafrente.png')
            )
          ],
        title: Text("Minha Pagina Web"),
      ),
0
投票

'WillPopScope'
已弃用，不应使用。请改用 PopScope。此功能在 v3.12.0-1.0.pre 之后已弃用。 （文档）

    @override
      Widget build(BuildContext context) {
        return PopScope(
          canPop: false,
          onPopInvoked: (bool didPop) {
            if (didPop) {
              return;
            }
            onPopScopePressBackShowAlertDialog();
          },
          child: Scaffold()
    );
}


exit(0);
离开申请

Future onPopScopePressBackShowAlertDialog() async {
  if (await webViewController.canGoBack()) {
    webViewController.goBack();
  } else {
    showDialog(
        context: context,
        barrierDismissible: false,
        builder: (BuildContext context) {
          return AlertDialog(
           title: Text('Are you sure you want to close the application?',
    textAlign: TextAlign.center,
  ),
  contentPadding:
  const EdgeInsets.only(left: 10.0, right: 10.0, top: 5.0, bottom: 5.0),
  actions: <Widget>[
    TextButton(
      child: Text('Leave'),
      onPressed: () {
        exit(0);
      },
    ),
    ElevatedButton(
      style: ElevatedButtonNormal(context),
      child: Text('Stay'),
      onPressed: () {
        Navigator.pop(context);
      },
    ),
  ],
);
        });
  }
}
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