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
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。
我为小部件状态创建了一个基类
使用BaseState<LoginPage>代替State<LoginPage> 然后使用布尔变量isOnline
Text(isOnline ? 'is Online' : 'is Offline')
首先，添加连接性插件:
dependencies:
connectivity: ^0.4.3+2
然后添加BaseState类
import 'dart:async';
import 'dart:io';
import 'package:flutter/services.dart';
import 'package:connectivity/connectivity.dart';
import 'package:flutter/widgets.dart';
/// a base class for any statful widget for checking internet connectivity
abstract class BaseState<T extends StatefulWidget> extends State {
void castStatefulWidget();
final Connectivity _connectivity = Connectivity();
StreamSubscription<ConnectivityResult> _connectivitySubscription;
/// the internet connectivity status
bool isOnline = true;
/// initialize connectivity checking
/// Platform messages are asynchronous, so we initialize in an async method.
Future<void> initConnectivity() async {
// Platform messages may fail, so we use a try/catch PlatformException.
try {
await _connectivity.checkConnectivity();
} on PlatformException catch (e) {
print(e.toString());
}
// If the widget was removed from the tree while the asynchronous platform
// message was in flight, we want to discard the reply rather than calling
// setState to update our non-existent appearance.
if (!mounted) {
return;
}
await _updateConnectionStatus().then((bool isConnected) => setState(() {
isOnline = isConnected;
}));
}
@override
void initState() {
super.initState();
initConnectivity();
_connectivitySubscription = Connectivity()
.onConnectivityChanged
.listen((ConnectivityResult result) async {
await _updateConnectionStatus().then((bool isConnected) => setState(() {
isOnline = isConnected;
}));
});
}
@override
void dispose() {
_connectivitySubscription.cancel();
super.dispose();
}
Future<bool> _updateConnectionStatus() async {
bool isConnected;
try {
final List<InternetAddress> result =
await InternetAddress.lookup('google.com');
if (result.isNotEmpty && result[0].rawAddress.isNotEmpty) {
isConnected = true;
}
} on SocketException catch (_) {
isConnected = false;
return false;
}
return isConnected;
}
}
您需要像这样在您的状态下强制转换小部件
@override
void castStatefulWidget() {
// ignore: unnecessary_statements
widget is StudentBoardingPage;
}
在@dennmatt的回答之后，我注意到InternetAddress。查找可能会返回成功的结果，即使互联网连接断开-我测试它从我的模拟器连接到我的家庭WiFi，然后断开我的路由器的电缆。我认为原因是路由器缓存了域查找结果，所以它不必在每个查找请求时查询DNS服务器。
不管怎样，如果你像我一样使用Firestore，你可以用一个空事务替换try-SocketException-catch块并捕获TimeoutExceptions:
try {
await Firestore.instance.runTransaction((Transaction tx) {}).timeout(Duration(seconds: 5));
hasConnection = true;
} on PlatformException catch(_) { // May be thrown on Airplane mode
hasConnection = false;
} on TimeoutException catch(_) {
hasConnection = false;
}
另外，请注意，previousConnection是在async internet -check之前设置的，因此理论上，如果checkConnection()在短时间内被调用多次，那么在一行中可能有多个hasConnection=true或多个hasConnection=false。 我不确定@dennmatt是否故意这样做，但在我们的用例中没有副作用(setState只被调用两次，具有相同的值)。
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
我几乎读了所有的帖子，@dennmat的帖子对我最有用。虽然它对我没用，而且也过时了。我有更新颤振更新连接包(I。E connectivity_plus)和data_connection_checker(检查移动和wifi是否有实际的互联网连接)。 在这篇文章之后，你将能够连续监听互联网连接。
1. 添加依赖关系 A)连通性:^1.0.6 B) data_connection_checker: ^0.3.4
2. 处理所有连接的自定义类。
import 'dart:async';
import 'package:connectivity_plus/connectivity_plus.dart';
import 'package:data_connection_checker/data_connection_checker.dart';
class ConnectionUtil {
//This creates the single instance by calling the `_internal` constructor specified below
static final ConnectionUtil _singleton = new ConnectionUtil._internal();
ConnectionUtil._internal();
//This is what's used to retrieve the instance through the app
static ConnectionUtil getInstance() => _singleton;
//This tracks the current connection status
bool hasConnection = false;
//This is how we'll allow subscribing to connection changes
StreamController connectionChangeController = StreamController();
//flutter_connectivity
final Connectivity _connectivity = Connectivity();
void initialize() {
_connectivity.onConnectivityChanged.listen(_connectionChange);
}
//flutter_connectivity's listener
void _connectionChange(ConnectivityResult result) {
hasInternetInternetConnection();
}
Stream get connectionChange => connectionChangeController.stream;
Future<bool> hasInternetInternetConnection() async {
bool previousConnection = hasConnection;
var connectivityResult = await (Connectivity().checkConnectivity());
//Check if device is just connect with mobile network or wifi
if (connectivityResult == ConnectivityResult.mobile ||
connectivityResult == ConnectivityResult.wifi) {
//Check there is actual internet connection with a mobile network or wifi
if (await DataConnectionChecker().hasConnection) {
// Network data detected & internet connection confirmed.
hasConnection = true;
} else {
// Network data detected but no internet connection found.
hasConnection = false;
}
}
// device has no mobile network and wifi connection at all
else {
hasConnection = false;
}
// The connection status changed send out an update to all listeners
if (previousConnection != hasConnection) {
connectionChangeController.add(hasConnection);
}
return hasConnection;
}
}
检查任何地方的连接并倾听变化。
@override
initState() {
print('called');
//Create instance
ConnectionUtil connectionStatus = ConnectionUtil.getInstance();
//Initialize
connectionStatus.initialize();
//Listen for connection change
_connectionChangeStream = connectionStatus.connectionChange.listen((event) {
print(event);
});
super.initState();
}
切换飞行模式时检查日志。你应该得到有true和false值的日志。
注意:这将无法在flutter web工作，如果你想让它工作，请使用dio或http插件而不是data_connection_checker。
项目示例可以在这里找到。谢谢
