我使用此代码检查互联网。我也将这个函数包装到 initState 中。当互联网不可用时， snackbar 始终显示。但是联网后， snackbar 并没有消失。我不能使用连接插件，因为他们在 Android 上说，该插件不能保证连接到互联网。

 checking1(TextEditingController usernameController, BuildContext context,
      String _url, GlobalKey<ScaffoldState> _scaffoldKey) async {
    try {
      final result = await InternetAddress.lookup('google.com');
      if (result.isNotEmpty && result[0].rawAddress.isNotEmpty) {
        usernameController.text == '' ?
        showDialog(...some code...) :
        usernameValidation(usernameController.text, context, _url);
      }
    }
    on SocketException
    catch (_) {
      _showSnackBar(_scaffoldKey);
    }
  }

最佳答案

完整示例演示了互联网连接及其来源的监听器。

Original post

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

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

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  Map _source = {ConnectivityResult.none: false};
  MyConnectivity _connectivity = MyConnectivity.instance;

  @override
  void initState() {
    super.initState();
    _connectivity.initialise();
    _connectivity.myStream.listen((source) {
      setState(() => _source = source);
    });
  }

  @override
  Widget build(BuildContext context) {
    String status = "Offline";
    switch (_source.keys.toList()[0]) {
      case ConnectivityResult.none:
        status = "Offline";
        break;
      case ConnectivityResult.mobile:
        status = "Mobile: Online";
        break;
      case ConnectivityResult.wifi:
        status = "WiFi: Online";
        break;
      case ConnectivityResult.ethernet:
        status = "Ethernet: Online";
        break;
    }

    return Scaffold(
      appBar: AppBar(title: Text("Internet")),
      body: Center(child: Text(status)),
    );
  }

  @override
  void dispose() {
    _connectivity.disposeStream();
    super.dispose();
  }
}

class MyConnectivity {
  MyConnectivity._internal();

  static final MyConnectivity _instance = MyConnectivity._internal();

  static MyConnectivity get instance => _instance;

  Connectivity connectivity = Connectivity();

  StreamController 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');
      if (result.isNotEmpty && result[0].rawAddress.isNotEmpty) {
        isOnline = true;
      } else {
        isOnline = false;
      }
    } on SocketException catch (_) {
      isOnline = false;
    }
    controller.sink.add({result: isOnline});
  }

  void disposeStream() => controller.close();
}

关于dart - 如何在 Flutter 上持续检查互联网连接与否？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/55060998/