add structure

lib/widget/offline_redirect.dart

@@ -0,0 +1,52 @@
+import 'dart:async';
+
+import 'package:flutter/material.dart';
+import 'package:provider/provider.dart';
+import 'package:fcs/model/main_model.dart';
+
+class OfflineRedirect extends StatefulWidget {
+  final Widget child;
+  OfflineRedirect({@required this.child});
+
+  @override
+  _OfflineRedirectState createState() => _OfflineRedirectState();
+}
+
+class _OfflineRedirectState extends State<OfflineRedirect> {
+  Timer offlineTimer;
+
+  @override
+  void initState() {
+    super.initState();
+  }
+
+  @override
+  void didChangeDependencies() {
+    _startOfflineTimer();
+    super.didChangeDependencies();
+  }
+
+  _startOfflineTimer() async {
+    if (offlineTimer!=null && offlineTimer.isActive) return;
+    var _duration = new Duration(milliseconds: 500);
+    this.offlineTimer = new Timer.periodic(_duration, offlineNav);
+  }
+
+  Future<void> offlineNav(Timer timer) async {
+    MainModel mainModel = Provider.of<MainModel>(context, listen: false);
+    if (!mainModel.isOnline) {
+      timer.cancel();
+      Navigator.pushNamedAndRemoveUntil(context, "/", (r) => false);
+    }
+  }
+
+  void dispose() {
+    offlineTimer.cancel();
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return widget.child;
+  }
+}