如果在 Flutter android 中使用 webview 页面时互联网连接丢失，则显示消息“无互联网”

Question

bool connectionStatus = true;
Future check() async {
  try {
    final result = await InternetAddress.lookup('google.com');
    if (result.isNotEmpty && result[0].rawAddress.isNotEmpty) {
      connectionStatus = true;
    }
  } on SocketException catch (_) {
    connectionStatus = false;
  }
}

class _BackButtonState extends State<BackButton> {
  DateTime backbuttonpressedTime;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: PreferredSize(
        preferredSize: Size(double.infinity, 0),
        child: AppBar(
          title: Text(""),
          backgroundColor: Colors.deepPurple,
        ),
      ),
      body: FutureBuilder(
          future: check(), // a previously-obtained Future or null
          builder: (BuildContext context, AsyncSnapshot<dynamic> snapshot) {
            if (connectionStatus == true) {
              return WillPopScope(
                onWillPop: onWillPop,
                child: WebviewScaffold(
                  url: 'https://www.theonlineindia.co.in',
                  hidden: true,
                  initialChild: Container(
                    child: const Center(
                      child: CircularProgressIndicator(
                          valueColor:
                              AlwaysStoppedAnimation<Color>(Colors.deepPurple)),
                    ),
                  ),
                ),
              );
            } else {
              return Center(
                  child: Column(
                mainAxisAlignment: MainAxisAlignment.center,
                crossAxisAlignment: CrossAxisAlignment.center,
                children: <Widget>[
                  Container(
                    child: Text('No internet connection !!!',
                        style: TextStyle(
                          // your text
                          fontFamily: 'Aleo',
                          fontStyle: FontStyle.normal,
                          fontWeight: FontWeight.bold,
                          fontSize: 25.0,
                        )),
                  ),
                  /* RaisedButton(
                    onPressed: () {
                      setState(() {});
                    },
                    color: Color(0xFF673AB7),
                    textColor: Colors.white,
                    child: Text('Refresh'),
                  ), */
                  // your button beneath text
                ],
              ));
            }
          }),
    );
  }

  Future<bool> onWillPop() async {
    DateTime currentTime = DateTime.now();

    //ifbackbuttonhasnotbeenpreedOrToasthasbeenclosed
    //Statement 1 Or statement2
    bool backButton = backbuttonpressedTime == null ||
        currentTime.difference(backbuttonpressedTime) > Duration(seconds: 2);
    if (backButton) {
      backbuttonpressedTime = currentTime;
      Fluttertoast.showToast(
          msg: "Double tap to exit the app",
          backgroundColor: Colors.deepPurple,
          textColor: Colors.white);
      return false;
    }
    exit(0);
    return true;
  }
}

在上面的代码中，我只能在启动应用程序时显示消息“没有互联网”。 我想在应用程序启动后显示相同的消息，如果在访问 webview 中的网页时互联网连接丢失。

我宁愿通过代码本身而不是寻找任何插件来实现上述目标。插件将是次要选项。

*

Answer 1

选项 1

定义一个定期检查连接的计时器

  const period= const Duration(seconds:5);
  new Timer.periodic(period, (Timer t) => check());

选项 2

使用connectivity 插件并在您的应用主小部件中定义一个流

    StreamSubscription<ConnectivityResult> networkSubscription;
    @override
      void initState() {
        super.initState();
        networkSubscription = Connectivity().onConnectivityChanged.listen((ConnectivityResult result) {
          check();
        });
        checkNetwork(); // Needed for the check on start
      }