连接插件在其文档中声明，它只在有网络连接的情况下提供信息，但不包括网络连接到Internet的情况。使用下面的代码，不要忘记使用“.timeout()”，因为使用“await”可能会永远卡住。

import 'dart:io';

Future<bool> isConnected() async {
  try {
    List<InternetAddress> result = await InternetAddress.lookup('example.com')
        .timeout(Duration(seconds: 5));

    //
    if (result.isNotEmpty && result[0].rawAddress.isNotEmpty) {
      return true;
    }
    //
    else {
      return false;
    }
  } on SocketException catch (_) {
    return false;
  }
}

Null安全代码:

One time check: Create this method: Future<bool> hasNetwork() async { try { final result = await InternetAddress.lookup('example.com'); return result.isNotEmpty && result[0].rawAddress.isNotEmpty; } on SocketException catch (_) { return false; } } Usage: bool isOnline = await hasNetwork(); Setting up a listener: Add the following dependency to your pubspec.yaml file. connectivity_plus: ^2.0.2 Full code: void main() => runApp(MaterialApp(home: HomePage())); class HomePage extends StatefulWidget { @override _HomePageState createState() => _HomePageState(); } class _HomePageState extends State<HomePage> { Map _source = {ConnectivityResult.none: false}; final MyConnectivity _connectivity = MyConnectivity.instance; @override void initState() { super.initState(); _connectivity.initialise(); _connectivity.myStream.listen((source) { setState(() => _source = source); }); } @override Widget build(BuildContext context) { String string; switch (_source.keys.toList()[0]) { case ConnectivityResult.mobile: string = 'Mobile: Online'; break; case ConnectivityResult.wifi: string = 'WiFi: Online'; break; case ConnectivityResult.none: default: string = 'Offline'; } return Scaffold( body: Center(child: Text(string)), ); } @override void dispose() { _connectivity.disposeStream(); super.dispose(); } } class MyConnectivity { MyConnectivity._(); static final _instance = MyConnectivity._(); static MyConnectivity get instance => _instance; final _connectivity = Connectivity(); final _controller = StreamController.broadcast(); Stream get myStream => _controller.stream; void initialise() async { ConnectivityResult result = await _connectivity.checkConnectivity(); _checkStatus(result); _connectivity.onConnectivityChanged.listen((result) { _checkStatus(result); }); } void _checkStatus(ConnectivityResult result) async { bool isOnline = false; try { final result = await InternetAddress.lookup('example.com'); isOnline = result.isNotEmpty && result[0].rawAddress.isNotEmpty; } on SocketException catch (_) { isOnline = false; } _controller.sink.add({result: isOnline}); } void disposeStream() => _controller.close(); }

截图:

来源:connectivity_plus和Günter Zöchbauer

对我来说，我只是在Firebase中创建一个数据，并使用未来构建器来等待数据。在这里，就像这样，你可以检查连接是否太慢，所以数据将被加载:

FutureBuilder(
    future: _getImage(context),
    builder: (context, snapshot) {
      switch (snapshot.connectionState) {
        case ConnectionState.none:
          return Text('Press button to start.');
        case ConnectionState.active:
        case ConnectionState.waiting:
          return Container(
              height:
                  MediaQuery.of(context).size.height / 1.25,
              width:
                  MediaQuery.of(context).size.width / 1.25,
              child: Loading());
        case ConnectionState.done:
          if (snapshot.hasData) {
            return snapshot.data;
          } else {
            return FlatButton(
              onPressed: () {
                Navigator.push(
                    context,
                    MaterialPageRoute(
                        builder: (context) =>
                            ProfilePage()));
              },
              child: Icon(
                Icons.add_a_photo,
                size: 50,
              ),
            );
          }
        // You can reach your snapshot.data['url'] in here
      }
      return null;
    },
  ),

基于这个答案https://stackoverflow.com/a/68436867/10761151

如果你使用dart零安全，你会得到一个错误， 因此，您可以将依赖项data_connection_checker: ^0.3.4更新为internet_connection_checker: ^0.0.1+2

你可以用这个代码

import 'dart:async';
import 'package:connectivity_plus/connectivity_plus.dart';
import 'package:internet_connection_checker/internet_connection_checker.dart';

class ConnectionUtil {
  static final ConnectionUtil _singleton = new ConnectionUtil._internal();
  ConnectionUtil._internal();

  static ConnectionUtil getInstance() => _singleton;

  bool hasConnection = false;

  StreamController connectionChangeController = StreamController();

  final Connectivity _connectivity = Connectivity();
  void initialize() {
    _connectivity.onConnectivityChanged.listen(_connectionChange);
  }

  void _connectionChange(ConnectivityResult result) {
    _hasInternetInternetConnection();
  }

  Stream get connectionChange => connectionChangeController.stream;
  Future<bool> _hasInternetInternetConnection() async {
    bool previousConnection = hasConnection;
    var connectivityResult = await (Connectivity().checkConnectivity());
    if (connectivityResult == ConnectivityResult.mobile || connectivityResult == ConnectivityResult.wifi) {
      // this is the different
      if (await InternetConnectionChecker().hasConnection) {
        hasConnection = true;
      } else {
        hasConnection = false;
      }
    } else {
      hasConnection = false;
    }

    if (previousConnection != hasConnection) {
      connectionChangeController.add(hasConnection);
    }
    return hasConnection;
  }
}

在有状态小部件上可以实现此代码

  bool hasInterNetConnection = false;

  @override
  initState() {
    ConnectionUtil connectionStatus = ConnectionUtil.getInstance();
    connectionStatus.initialize();
    connectionStatus.connectionChange.listen(connectionChanged);

    super.initState();
  }

  void connectionChanged(dynamic hasConnection) {
    setState(() {
      hasInterNetConnection = hasConnection;
    });
  }

使用observe_internet_connectivity包。

可用的特性

检查设备是否有互联网连接

  final hasInternet = await InternetConnectivity().hasInternetConnection;
  if (hasInternet) {
    //You are connected to the internet
  } else {
    //"No internet connection
  }

通过流收听互联网连接变化

  final subscription =
      InternetConnectivity().observeInternetConnection.listen((bool hasInternetAccess) {
        if(!hasInternetAccess){
          showToast('No Internet Connection');
        }
      });

   await Future.delayed(const Duration(seconds: 10 ));
   subscription.cancel();

使用InternetConnectivityListener监听flutter小部件内的互联网连接变化

    return InternetConnectivityListener(
      connectivityListener: (BuildContext context, bool hasInternetAccess) {
        if (hasInternetAccess) {
          context.showBanner('You are back Online!', color: Colors.green);
        } else {
          context.showBanner('No internet connection', color: Colors.red);
        }
      },
      child: Scaffold(
        body: Container(),
      ),
    );

使用InternetConnectivityBuilder构建互联网连接感知小部件

    return InternetConnectivityBuilder(
      connectivityBuilder: (BuildContext context, bool hasInternetAccess, Widget? child) { 
        if(hasInternetAccess) {
          return OnlineWidget();
        } else {
          return OfflineWidget();
        }
      },
      child: ChildWidget(),
    );

连接插件在其文档中声明，它只在有网络连接的情况下提供信息，但不包括网络连接到Internet的情况

请注意，在Android上，这并不保证连接到互联网。例如，应用程序可能有wifi接入，但它可能是一个VPN或酒店wifi，没有接入。

你可以使用

import 'dart:io';
...
try {
  final result = await InternetAddress.lookup('example.com');
  if (result.isNotEmpty && result[0].rawAddress.isNotEmpty) {
    print('connected');
  }
} on SocketException catch (_) {
  print('not connected');
}

更新

不建议使用连接包。请使用官方的Flutter Community connectivity_plus包。