我有一个网络调用要执行。但在此之前，我需要检查设备是否有互联网连接。
这是我目前为止所做的:
var connectivityResult = new Connectivity().checkConnectivity();// User defined class
if (connectivityResult == ConnectivityResult.mobile ||
connectivityResult == ConnectivityResult.wifi) {*/
this.getData();
} else {
neverSatisfied();
}
上述方法行不通。
当前回答
我发现仅仅使用连接包不足以判断互联网是否可用。在安卓系统中，它只会检查是否有WIFI或移动数据是否打开，而不会检查是否有实际的互联网连接。在我的测试中，即使没有移动信号ConnectivityResult。Mobile将返回true。
在IOS系统中，我的测试发现，连接插件在手机没有信号的情况下能够正确地检测出是否有网络连接，而Android系统中才存在这个问题。
我找到的解决方案是使用data_connection_checker包以及连接性包。这只是通过向几个可靠的地址发出请求来确保有一个互联网连接，检查的默认超时时间大约是10秒。
我完成的isInternet函数看起来有点像这样:
Future<bool> isInternet() async {
var connectivityResult = await (Connectivity().checkConnectivity());
if (connectivityResult == ConnectivityResult.mobile) {
// I am connected to a mobile network, make sure there is actually a net connection.
if (await DataConnectionChecker().hasConnection) {
// Mobile data detected & internet connection confirmed.
return true;
} else {
// Mobile data detected but no internet connection found.
return false;
}
} else if (connectivityResult == ConnectivityResult.wifi) {
// I am connected to a WIFI network, make sure there is actually a net connection.
if (await DataConnectionChecker().hasConnection) {
// Wifi detected & internet connection confirmed.
return true;
} else {
// Wifi detected but no internet connection found.
return false;
}
} else {
// Neither mobile data or WIFI detected, not internet connection found.
return false;
}
}
if (await DataConnectionChecker(). hasconnection)部分对于移动连接和wifi连接都是一样的，可能应该移动到一个单独的函数。我在这里没有这样做是为了让它更易于阅读。
其他回答
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;
});
}
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;
},
),
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
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(),
);
我最终(虽然不情愿)选择了@abernee在之前回答这个问题时给出的解决方案。我总是尝试在我的项目中尽可能少地使用外部包——因为我知道外部包是我所创建的软件的唯一[潜在]故障点。所以链接到两个外部包只是为了一个简单的实现，像这样对我来说并不容易。
尽管如此，我还是采用了abernee的代码，并对其进行了修改，使其更精简、更合理。我说的明智是指他在自己的功能中消耗了Connectivity包的功能，但在内部由于没有从这个包中返回最有价值的输出(即网络标识)而浪费了它。这是阿伯尼解决方案的修改版本:
import 'package:connectivity/connectivity.dart';
import 'package:data_connection_checker/data_connection_checker.dart';
// 'McGyver' - the ultimate cool guy (the best helper class any app can ask for).
class McGyver {
static Future<Map<String, dynamic>> checkInternetAccess() async {
//* ////////////////////////////////////////////////////////////////////////////////////////// *//
//* INFO: ONLY TWO return TYPES for Map 'dynamic' value => <bool> and <ConnectivityResult> *//
//* ////////////////////////////////////////////////////////////////////////////////////////// *//
Map<String, dynamic> mapCon;
final String isConn = 'isConnected', netType = 'networkType';
ConnectivityResult conRes = await (Connectivity().checkConnectivity());
switch (conRes) {
case ConnectivityResult.wifi: //* WiFi Network: true !!
if (await DataConnectionChecker().hasConnection) { //* Internet Access: true !!
mapCon = Map.unmodifiable({isConn: true, netType: ConnectivityResult.wifi});
} else {
mapCon = Map.unmodifiable({isConn: false, netType: ConnectivityResult.wifi});
}
break;
case ConnectivityResult.mobile: //* Mobile Network: true !!
if (await DataConnectionChecker().hasConnection) { //* Internet Access: true !!
mapCon = Map.unmodifiable({isConn: true, netType: ConnectivityResult.mobile});
} else {
mapCon = Map.unmodifiable({isConn: false, netType: ConnectivityResult.mobile});
}
break;
case ConnectivityResult.none: //* No Network: true !!
mapCon = Map.unmodifiable({isConn: false, netType: ConnectivityResult.none});
break;
}
return mapCon;
}
}
然后你可以在代码中的任何地方通过简单的调用来使用这个静态函数，如下所示:
bool isConn; ConnectivityResult netType;
McGyver.checkInternetAccess().then(
(mapCIA) { //* 'mapCIA' == amalgamation for 'map' from 'CheckInternetAccess' function result.
debugPrint("'mapCIA' Keys: ${mapCIA.keys}");
isConn = mapCIA['isConnected'];
netType = mapCIA['networkType'];
}
);
debugPrint("Internet Access: $isConn | Network Type: $netType");
遗憾的是，你必须链接到两个外部包才能在你的Flutter项目中获得这个非常基本的功能-但我想目前这是我们拥有的最好的。实际上，我更喜欢数据连接检查器包而不是连接包——但是(在发布这篇文章的时候)前者缺少我从连接包中需要的非常重要的网络识别功能。这就是我(暂时)默认采用这种方法的原因。
