使用flutter webview作为主页并按下后退按钮关闭应用程序答案

【问题标题】：Using flutter webview as home and pressing back button closes Application使用flutter webview作为主页并按下后退按钮关闭应用程序
【发布时间】：2020-01-12 16:32:12
【问题描述】：

我正在尝试在 Flutter 中使用 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 web 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;
              },   
      ),

    );
  }
}`

【问题讨论】：

我认为这是使用 webview 插件时的预期行为，除非您知道任何文档另有说明。
你试过使用 WebViewController 类吗？使用 canGoBack 方法检查是否有返回历史记录，然后使用 goBack 方法返回上一页。
@FarhanSyah 好主意，我会查看 webview 控制器，看看是否存在返回方法，谢谢

标签： flutter webview flutter-dependencies

【解决方案1】：

onbackpressed Webview 的代码

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;
            },
          );
      },),

      ),
    );

【讨论】：

_controller 来自哪里？是的，它不存在。删除这个
"返回 Future.value(false);"应该在 if/else 语句之外

【解决方案2】：

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);
    }
  }
}

【讨论】：

虽然此代码可能会回答问题，但提供有关它如何和/或为什么解决问题的额外上下文将提高答案的长期价值。

【解决方案3】：

您必须控制 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,
        )),
      ),
    );
  }
}

【讨论】：

【解决方案4】：

这是最好的答案（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'),
                  ),
                ],
              ));
    }
  }

这里是调用 WillPopScope

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

【讨论】：

【解决方案5】：

用 WillPopScope 包裹 Scaffold 并在用户单击设备返回按钮时执行 WebView Controller goback

code sn-p onwillpop

    @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),
          ],
        ),

退出应用的代码 sn-p

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。我单击桌面页面，然后按设备返回按钮，您可以看到信息显示“onwill goback”。并返回上一页

【讨论】：

pub.dev/packages/minimize_app 调用比Scaffold.of(context).showSnackBar(const SnackBar(content: Text("No back history item")),); 有用
@Yash 不是更好的答案。不使用 inappwebview
我想隐藏 appBar: AppBar.如果我删除 appBar - 后退导航不起作用。我该怎么办？
_exitApp()的返回值是不是顺序不对？如果应用程序应该返回而不是 webview，它不应该返回 true 吗？
这项工作！非常感谢！