在 Flutter 应用程序上持续检查互联网断开连接

Question

我正在 Flutter 上创建一个移动应用程序，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 数据库。

到目前为止，我已经使用 connectivity 0.3.2 来在异步调用或登录操作之前检查网络连接。就像下面的例子：

    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");}

}

我想问问有没有什么办法可以在用户使用应用的每一个瞬间持续检查网络断开（即使他只是在读数据，不用打一个 API 电话）。

为了通知用户他离线了，比如用一个SnackBar。

Answer 1

您已经编写了代码来执行您想要的操作。您可以轻松地将其包装在一个页面 State 或 InheritedWidget 或其他页面中其他管理 class.

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，只要 onConnectivityChanged 发生变化，它就会更新为新结果，这意味着您只需监听变化，而无需手动查询。

文档摘录：

You can also listen for network state changes by subscribing to the stream exposed by connectivity plugin

Answer 2

我刚刚实现了这个包 https://pub.dartlang.org/packages/flutter_offline 来处理这个问题非常简单。

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

您将其包含在您的项目中并开始使用该库，如下例所示：

之后，您将 OfflineBuilder 添加到 Widget build(BuildContext context) { 它会从 ConnectivityResult 读取所有流更改，即使用户根本没有与应用程序交互（或仅读取数据）和连接状态更改也是如此。

    @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

您的 pubspec.yaml，添加以下行：

flutter_offline: "^0.3.0"

导入

import 'package:flutter_offline/flutter_offline.dart';

例子：

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"),
                ),
              );
            },
          )),
    );
  }
}

在 Flutter 应用程序上持续检查互联网断开连接

Continuously check internet disconnection on Flutter app

dart

flutter

connectivity