main.dart

  void main() => runApp(DemoApp());

  class DemoApp extends StatelessWidget {
    const DemoApp();

    @override
    Widget build(BuildContext context) {
      return MaterialApp(
        home: Scaffold(
            appBar: AppBar(
              title: const Text("Checking the connection"),
            ),
            body: const Center(
              child: ConnectionWidget(),
            )
        ),
      );
    }

  }
  

connection_widget.dart

  class ConnectionWidget extends StatelessWidget {
    static final _conn = Connectivity();
    const ConnectionWidget();

    @override
    Widget build(BuildContext context) {
      return StreamBuilder<ConnectivityResult>(
        stream: _conn.onConnectivityChanged,
        builder: (context, status) {
          if (status.hasData) {
            final data = status.data;

            if (data != null) {
              switch (data) {
                case ConnectivityResult.wifi:
                  return const WifiConnectionWidget();
                case ConnectivityResult.mobile:
                  return const MobileConnectionWidget();
                case ConnectivityResult.none:
                  return const NoConnectionWidget();
              }
            } else {
              debugPrint("Whoops");
            }
          }

          return const CircularProgressIndicator();
        },
      );
    }
  }
  

wifi_connection.dart

  class WifiConnectionWidget extends StatelessWidget {
    const WifiConnectionWidget();

    @override
    Widget build(BuildContext context) {
      return Wrap(
        spacing: 20,
        crossAxisAlignment: WrapCrossAlignment.center,
        direction: Axis.vertical,
        children: const <Widget>[
          Icon(Icons.wifi,
            color: Colors.lightGreen,
            size: 35,
          ),

          Text("Connected to WiFi")
        ],
      );
    }
  }
  

mobile_connection.dart

  class MobileConnectionWidget extends StatelessWidget {
    const MobileConnectionWidget();

    @override
    Widget build(BuildContext context) {
      return Wrap(
        spacing: 20,
        crossAxisAlignment: WrapCrossAlignment.center,
        direction: Axis.vertical,
        children: const <Widget>[
          Icon(Icons.network_cell,
            color: Colors.lightBlue,
            size: 35,
          ),

          Text("Connected via cellular")
        ],
      );
    }
  }
  

no_connection.dart

  class NoConnectionWidget extends StatelessWidget {
    const NoConnectionWidget();

    @override
    Widget build(BuildContext context) {
      return Wrap(
        spacing: 20,
        crossAxisAlignment: WrapCrossAlignment.center,
        direction: Axis.vertical,
        children: const <Widget>[
          Icon(Icons.error_outline,
            color: Colors.red,
            size: 35,
          ),

          Text("Not connected")
        ],
      );
    }
  }