merge:

app/lib/data_classes.dart

@@ -34,6 +34,7 @@ class Measurement {
 class SubDiv {
   String sub_div_id;
   int groupID;
+  String group_id;
   double minThickness;
   double avgThickness;
   LatLng center;
@@ -44,6 +45,7 @@ class SubDiv {
   SubDiv({
     required this.sub_div_id,
     required this.groupID,
+    required this.group_id,
     required this.minThickness,
     required this.avgThickness,
     required this.center,
@@ -56,6 +58,7 @@ class SubDiv {
     return SubDiv(
       sub_div_id: json['SubdivID'].toString(),
       groupID: json['GroupID'],
+      group_id: '', // Initialise empty, will be set later
       minThickness: json['MinThickness'],
       avgThickness: json['AvgThickness'],
       center: LatLng(json['CenLatitude'], json['CenLongitude']),

app/lib/main.dart

-import 'package:flutter/material.dart';
 import 'pages/default_page.dart';
+import 'package:flutter/material.dart';
 
 void main() {
   runApp(const MyApp());

app/lib/pages/consts.dart

-import 'package:flutter/material.dart';
-import 'package:google_fonts/google_fonts.dart';
-import 'package:latlong2/latlong.dart';
-
-// API variables
-const String port = "8443";
-const String serverURI = "https://127.0.0.1:$port/";
-const String mapEndpoint = "update_map";
-const int fetchInterval = 60; // Fetch marker data every n minutes
-
-// Map variables
-LatLng mapCenter = LatLng(60.7666, 10.8471);
-DateTime ?lastUpdate; // Last time data was fetched from server
-
-// Font variables
-const textColor = Colors.white;
-final appTitleStyle = GoogleFonts.dmSans(
-  fontSize: 35,
-  color: Colors.black,
-  fontWeight: FontWeight.bold,
-);
-final titleStyle = GoogleFonts.dmSans(
-  fontSize: 35,
-  color: textColor,
-  fontWeight: FontWeight.bold,
-);
-final regTextStyle = GoogleFonts.dmSans(fontSize: 19, color: textColor);
-final chartTextStyle = GoogleFonts.dmSans(fontSize: 14, color: textColor);
-final subHeadingStyle = GoogleFonts.dmSans(fontSize: 22, color: textColor, fontWeight: FontWeight.bold);
-
-// Colors
-const darkBlue = Color(0xFF015E8F);
-const teal = Color(0xFF00B4D8);
-const darkestBlue = Color(0xFF03045E);
-const lightBlue = Color(0xFFCAF0F8);
-const superLightBlue = Color(0xFFCAF0F8);
-const barBlue = Color(0xFF0077B6);
\ No newline at end of file

app/lib/pages/default_page.dart

 import 'dart:async';
 import 'package:flutter/material.dart';
-import 'widgets/map_widget.dart';
-import 'marker_handler/marker_data.dart';
-import 'consts.dart';
-import 'marker_handler/get_markers.dart';
-import 'marker_handler/get_relation.dart';
 import 'dart:typed_data';
 
+import '../consts.dart';
+import '../widgets/main_layout.dart';
+import '../data_classes.dart';
+import '../server_requests/fetch_markers.dart';
+import '../server_requests/fetch_relation.dart';
+
 class DefaultPage extends StatefulWidget {
   const DefaultPage({Key? key}) : super(key: key);
 
@@ -18,6 +19,7 @@ class _DefaultPageState extends State<DefaultPage> {
   late Timer _timer;
   bool showBar = false;
   bool serverConnection = true;
+  bool dialogShown = false;
 
   late Future<List<Measurement>> markerListFuture;
   late Future<Uint8List> relationFuture;
@@ -26,35 +28,62 @@ class _DefaultPageState extends State<DefaultPage> {
   void initState() {
     super.initState();
     // Try to fetch measurement data from server
-    markerListFuture = fetchMarkerData().then((fetchResult) {
+    markerListFuture = fetchMeasurements().then((fetchResult) {
       List<Measurement> measurements = fetchResult.measurements;
       serverConnection = fetchResult.connected;
 
       // Return the measurements
       return measurements;
     }).catchError((error) {
+      serverConnection = false;
       throw Exception("Failed to fetch measurements: $error");
     });
 
-
+    // Attempt to fetch relation from server if app establishes connection
+    if (serverConnection){
       relationFuture = fetchRelation();
-    //relationFuture = Future.value(Uint8List(0));
+    } else { // Read last saved data
+      relationFuture =  loadSavedRelation();
+    }
 
-    // Schedule fetchMarkerData to run periodically based on fetchInterval from consts
+    // Schedule fetchMarkerData to run periodically based on fetchInterval
     const Duration interval = Duration(minutes: fetchInterval); // NB fetchInterval value to be determined
     _timer = Timer.periodic(interval, (timer) {
-      fetchMarkerData();
+      fetchMeasurements();
     });
   }
 
-  // Fetch-interval timer
   @override
   void dispose() {
-    // Cancel timer on widget termination
     _timer.cancel();
     super.dispose();
   }
 
+  /// Display message to user
+  void showConnectionMessage() {
+    showDialog(
+      context: context,
+      builder: (context) => AlertDialog(
+        actions: [
+          TextButton(
+            onPressed: () {
+              Navigator.of(context).pop();
+              },
+            child: const Text("Ok"),
+          )
+        ],
+        title: const Center(
+          child: Text("No server connection")
+        ),
+        contentPadding: const EdgeInsets.all(10.0),
+        content: const Text(
+          "The app may display outdated information. Use with caution!",
+          textAlign: TextAlign.center, // Align text center
+        ),
+      ),
+    );
+  }
+
   @override
   Widget build(BuildContext context) {
     return MaterialApp(
@@ -75,22 +104,36 @@ class _DefaultPageState extends State<DefaultPage> {
         body: FutureBuilder(
           future: Future.wait([markerListFuture, relationFuture]),
           builder: (BuildContext context, AsyncSnapshot<List<dynamic>> snapshot) {
-            // Display loading screen until data is fetched
+            // Display loading screen while app state is being set
             if (snapshot.connectionState == ConnectionState.waiting) {
-              return const Center(child: Icon(
-                  Icons.severe_cold,
-                  color: Colors.blue,
-                  size: 100,
-              ));
+              return Container(
+                decoration: const BoxDecoration( // Loading screen
+                  color: darkestBlue,
+                ),
+                child: Center(
+                  child: Image.asset(
+                    'assets/icons/frozen.png', // Loading screen icon
+                    // Icon from: https://www.flaticon.com/free-icons/cold-water"
+                    color: lightBlue,
+                    width: 170,
+                    height: 170,
+                  ),
+                ),
+              );
             } else if (snapshot.hasError) {
               return Center(child: Text('Error: ${snapshot.error}'));
             } else {
-              if (!serverConnection) { // NB: implement alert
-                print("Failed to connect to server");
+              // If no server connection, alert user upon completing build
+              WidgetsBinding.instance.addPostFrameCallback((_) {
+                if (!serverConnection && !dialogShown) {
+                  dialogShown = true;
+                  showConnectionMessage();
                 }
-              // Display default page once all data is loaded from server
+              });
+
               List<Measurement> markerList = snapshot.data![0] as List<Measurement>;
               Uint8List relation = snapshot.data![1] as Uint8List;
+
               return Container( // Return container with list view and background color
                 decoration: const BoxDecoration( // Set background color
                   gradient: LinearGradient(
@@ -101,7 +144,11 @@ class _DefaultPageState extends State<DefaultPage> {
                 ),
                 child: ListView(
                   children: [
-                    MapContainerWidget(markerList: markerList, relation: relation),
+                    MapContainerWidget(
+                      markerList: markerList,
+                      relation: relation,
+                      serverConnection: serverConnection,
+                    ),
                   ],
                 ),
               );
@@ -112,4 +159,3 @@ class _DefaultPageState extends State<DefaultPage> {
     );
   }
 }
-

app/lib/pages/marker_handler/get_markers.dart

-import 'dart:async';
-import 'dart:convert';
-import 'dart:io';
-import '../consts.dart';
-import 'marker_data.dart';
-import 'package:path_provider/path_provider.dart';
-import 'package:shared_preferences/shared_preferences.dart';
-import 'package:flutter/material.dart';
-
-class FetchResult {
-  final List<Measurement> measurements;
-  final bool connected;
-
-  FetchResult(this.measurements, this.connected);
-}
-
-// fetchMarkerTemplate requests all marker data from the server
-Future<FetchResult> fetchMarkerData() async {
-  try {
-    // Custom HTTP client
-    HttpClient client = HttpClient()
-      ..badCertificateCallback = // NB: temporary disable SSL certificate validation
-          (X509Certificate cert, String host, int port) => true;
-
-    // Request markers from server
-    var request = await client.getUrl(Uri.parse(serverURI + mapEndpoint));
-    var response = await request.close(); // Close response body at end of function
-
-    // Parse body to JSON if request is ok
-    if (response.statusCode == 200) {
-      var responseBody = await response.transform(utf8.decoder).join();
-
-      if (responseBody.isNotEmpty) {
-        var jsonData = json.decode(responseBody);
-
-        // Attempt to parse response to Measurement object only if the body
-        // contains correctly formatted data
-        if (jsonData != null && jsonData is List) {
-          Directory appDocumentsDirectory = await getApplicationDocumentsDirectory();
-          String filePath = '${appDocumentsDirectory.path}/last_data.json';
-
-          try { // Write most recent time of update to file
-            await File(filePath).writeAsString(responseBody, mode: FileMode.write);
-            print('Lake data written to file');
-          } catch (error) { print('Error in writing to file: $error');}
-
-          // Update local and persistent lastUpdate variable
-          lastUpdate = DateTime.now();
-          final prefs = await SharedPreferences.getInstance();
-          await prefs.setString('lastUpdate', '${DateTime.now()}');
-
-          return FetchResult(jsonData.map((data) => Measurement.fromJson(data)).toList(), true);
-        }
-      }
-    }
-    return loadSavedData();
-  } catch (e) {
-    return loadSavedData();
-  }
-}
-
-Future<FetchResult> loadSavedData() async {
-  // Get latest saved data from file if the server does not respond
-  Directory appDocumentsDirectory = await getApplicationDocumentsDirectory();
-  String filePath = '${appDocumentsDirectory.path}/last_data.json';
-
-  // Read file contents
-  File file = File(filePath);
-  if (await file.exists()) {
-    String contents = await file.readAsString();
-    List<dynamic> jsonData = json.decode(contents); // Parse JSON string from file
-    List<Measurement> measurements = jsonData.map((data) => Measurement.fromJson(data)).toList();
-    return FetchResult(measurements, false);
-  } else {
-    throw Exception('File does not exist');
-  }
-}