Implemented Loading Overlay

lib/pages/landing_page.dart

@@ -3,6 +3,7 @@ import 'package:provider/provider.dart';
 
 import '../widgets/flood_station_list_view.dart';
 import '../services/flood_station_provider.dart';
+import '../widgets/loading_notifier.dart';
 import '../widgets/station_filter.dart';
 import 'flood_station_page.dart';
 
@@ -17,11 +18,19 @@ class LandingPage extends StatefulWidget {
 
 class _LandingPageState extends State<LandingPage> {
   late FloodStationProvider floodStationProvider;
+  bool _isLoading = false;
+  OverlayEntry? _overlayEntry;
+
   @override
   initState() {
     super.initState();
-    WidgetsBinding.instance
-        .addPostFrameCallback((_) => floodStationProvider.loadAllStations());
+    WidgetsBinding.instance.addPostFrameCallback((_) {
+      _isLoading = true;
+      showLoadingNotifier(context: context, message: 'Loading');
+      floodStationProvider
+          .loadAllStations()
+          .whenComplete(() => removeLoadingNotifier());
+    });
   }
 
   @override
@@ -46,4 +55,35 @@ class _LandingPageState extends State<LandingPage> {
       ),
     );
   }
+
+  Future<void> showLoadingNotifier({
+    required BuildContext context,
+    required String message,
+  }) async {
+    OverlayState? overlayState = Overlay.of(context);
+    _overlayEntry = OverlayEntry(
+      builder: (c) {
+        return Positioned(
+          bottom: 16,
+          left: 0,
+          right: 0,
+          child: Center(
+            child: LoadingNotifier(
+              message: 'Loading',
+              onDismissed: () => removeLoadingNotifier(),
+            ),
+          ),
+        );
+      },
+    );
+    overlayState.insert(_overlayEntry!);
+    overlayState.setState(() {});
+  }
+
+  void removeLoadingNotifier() {
+    if (_overlayEntry != null) {
+      _overlayEntry?.remove();
+      _overlayEntry = null;
+    }
+  }
 }