不断检查 Flutter 应用程序上的互联网断开连接

Question

我正在 Flutter 上创建一个移动应用程序，并且我正在调用在 Node.js 上创建的 REST API，以便始终连接和查询我的 oracle DB。

到目前为止，我一直在使用 connectivity 0.3.2，以便在异步调用或登录操作之前检查网络连接。像下面的例子：

    checkConnectivity(context) async{

  String connectionStatus;
  StreamSubscription<ConnectivityResult> _connectivitySubscription;
  final Connectivity _connectivity = new Connectivity();
  try {
    connectionStatus = (await _connectivity.checkConnectivity()).toString();
    _connectivity.onConnectivityChanged.listen((ConnectivityResult result) {
      connectionStatus = result.toString();
      //   print(connectionStatus);
    });
  } on PlatformException catch (e) {
    print(e.toString());
    connectionStatus = 'Failed to get connectivity.';
  }
  if(connectionStatus == "ConnectivityResult.none"){
    components.alertPopup(context, "No Internet Connection available" , "Please check your internet connection and try again");}

}

我想问是否有任何可能的方法可以在用户使用应用程序的每一刻持续检查互联网断开（即使他只是在读取数据，而无需在全部）。

例如为了通知用户他离线了一个 SnackBar。

Answer 1

您的 pubspec.yaml，将以下行添加为：

flutter_offline: "^0.3.0"

导入

import 'package:flutter_offline/flutter_offline.dart';

示例：

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Scaffold(
          appBar: AppBar(
            title: Text("Connection status"),
          ),
          body: Builder(
            builder: (BuildContext context) {
              return OfflineBuilder(
                connectivityBuilder: (BuildContext context,
                    ConnectivityResult connectivity, Widget child) {
                  final bool connected =
                      connectivity != ConnectivityResult.none;
                  return Stack(
                    fit: StackFit.expand,
                    children: [
                      child,
                      Positioned(
                        left: 0.0,
                        right: 0.0,
                        height: 32.0,
                        child: AnimatedContainer(
                          duration: const Duration(milliseconds: 300),
                          color:
                              connected ? Colors.green : Colors.red,
                          child: connected
                              ? Row(
                                  mainAxisAlignment: MainAxisAlignment.center,
                                  children: <Widget>[
                                    Text(
                                      "YOU ARE OFFLINE",
                                      style: TextStyle(color: Colors.white),
                                    ),
                                  ],
                                )
                              : Row(
                                  mainAxisAlignment: MainAxisAlignment.center,
                                  children: <Widget>[
                                    Text(
                                      "YOU ARE OFFLINE",
                                      style: TextStyle(color: Colors.white),
                                    ),
                                    SizedBox(
                                      width: 8.0,
                                    ),
                                    SizedBox(
                                      width: 12.0,
                                      height: 12.0,
                                      child: CircularProgressIndicator(
                                        strokeWidth: 2.0,
                                        valueColor:
                                            AlwaysStoppedAnimation<Color>(
                                                Colors.white),
                                      ),
                                    ),
                                  ],
                                ),
                        ),
                      ),
                    ],
                  );
                },
                child: Center(
                  child: Text("ONLINE Or OFFLINE"),
                ),
              );
            },
          )),
    );
  }
}

Answer 2

我刚刚实现了这个包https://pub.dartlang.org/packages/flutter_offline，它非常简单地处理了这个问题。

第一步是导入包 导入'package:flutter_offline/flutter_offline.dart';

您包含在项目中并开始使用该库，如以下示例所示：

之后，您将 OfflineBuilder 包含在 Widget build(BuildContext context) { 它会从 ConnectivityResult 读取所有流的变化，即使用户根本没有与应用程序交互（或只是读取数据）并且连接状态发生变化。

    @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),
                label: Text("Barcode"),
                onPressed: _scanQR,
              ),
              new Container(
                // padding: EdgeInsets.only(left: 24.0, right: 24.0),
                child: Row(
                  mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                  children: [
                    Column(
                      children: [
                        Icon(Icons.hotel, color: Colors.blueGrey[600]),
                      ],
                    ),
                    Column(
                      children: [
                        Icon(Icons.hotel, color: Colors.blue[400]),
                      ],
                    ),
                  ],
                ),

                alignment: Alignment(0.0, 0.0),
              ),
            ],
          ),
          floatingActionButtonLocation: FloatingActionButtonLocation.centerFloat,
          drawer: MenuDrawer(),
        )
    );
  }

Answer 3

您已经编写了代码来做您想做的事。您可以轻松地将其包装在页面 State 或 InheritedWidget 或其他一些管理类中。

final Connectivity _connectivity;
final StreamSubscription<ConnectivityResult> _subscription;

ConstructorForWhateverClassThisIs() {
    _connectivity = new Connectivity();
    _subscription = _connectivity.onConnectivityChanged.listen(onConnectivityChange);
}

void onConnectivityChange(ConnectivityResult result) {
    // TODO: Show snackbar, etc if no connectivity
}

void dispose() {
    // Always remember to cancel your subscriptions when you're done.
    subscription.cancel();
}

根据documentation，onConnectivityChanged 将在新结果发生更改时更新，这意味着您只需侦听更改而无需手动查询。

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