How to continuously check internet connect or not on Flutter? - dart

Question

I use this code for check internet. and I wrap this function into initState also. Snack bar always displays when internet not available. But after connecting to the internet, the snack bar is not disappeared. I can't use connectivity plugin because they said on Android, the plugin does not guarantee connection to the Internet.
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);
}
}

Answer 1

Full example demonstrating a listener of the internet connectivity and its source.
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();
}

Answer 2

Another option also can be this package: https://pub.dartlang.org/packages/flutter_offline that deal with this issue really straightforward.
You need first to import the package 'package:flutter_offline/flutter_offline.dart';
After that you include the OfflineBuilder on Widget build(BuildContext context) and it will read all all stream changes from ConnectivityResult continuously.
Like the example on the link or like the following one
#override
Widget build(BuildContext context) {
return OfflineBuilder(
debounceDuration: Duration.zero,
connectivityBuilder: (
BuildContext context,
ConnectivityResult connectivity,
Widget child,
) {
if (connectivity == ConnectivityResult.none) {
return Scaffold(
appBar: AppBar(
title: const Text('Home'),
),
body: Center(child: Text('Please check your internet connection!')),
);
}
return child;
},
child: Scaffold(
resizeToAvoidBottomPadding: false,
appBar: AppBar(
title: Text("Home")
),
body: new Column(
children: <Widget>[
new Container(
decoration: new BoxDecoration(color: Theme.of(context).cardColor),
child: _buildTxtSearchBox(),
),
new Divider(height: 10.0),
new FloatingActionButton.extended(
icon: Icon(Icons.camera_alt),
),
new Container(
...
),
],
),
floatingActionButtonLocation: FloatingActionButtonLocation.centerFloat,
drawer: MenuDrawer(),
)
);
}

Answer 3

The connectivity package will do what you want. It has an onConnectivityChanged stream which you can subscribe to. This will notify your app when the connectivity state changes. But just because your device is connected to a network doesn't mean it can access your server and be connected. So a DNS lookup would be a good idea before then updating the internal state of your application.
https://pub.dartlang.org/documentation/connectivity/latest/connectivity/Connectivity-class.html

Answer 4

I find this to be reliable & more convincing :
Future<bool> connectivityChecker() async {
var connected = false;
print("Checking internet...");
try {
final result = await InternetAddress.lookup('google.com');
final result2 = await InternetAddress.lookup('facebook.com');
final result3 = await InternetAddress.lookup('microsoft.com');
if ((result.isNotEmpty && result[0].rawAddress.isNotEmpty) ||
(result2.isNotEmpty && result2[0].rawAddress.isNotEmpty) ||
(result3.isNotEmpty && result3[0].rawAddress.isNotEmpty)) {
print('connected..');
connected = true;
} else {
print("not connected from else..");
connected = false;
}
} on SocketException catch (_) {
print('not connected...');
connected = false;
}
return connected;
}
Based on the bool value of connected returned, I'd run a timer based loop to check for internet again & again till its connected. Open to any suggestions