added comments and refactored code

lib/widgets/map_popup.dart

@@ -5,14 +5,19 @@ import '../model/flood_station.dart';
 
 class MapPopup extends StatelessWidget {
   const MapPopup(
-      {super.key, required this.station, required this.onShowTapped});
-  final FloodStation station;
-  final Function() onShowTapped;
+      {super.key,
+      required FloodStation station,
+      required dynamic Function() onShowTapped})
+      : _onShowTapped = onShowTapped,
+        _station = station;
+
+  final FloodStation _station;
+  final Function() _onShowTapped;
 
   @override
   Widget build(BuildContext context) {
     return AlertDialog(
-      title: Text(station.label),
+      title: Text(_station.label),
       content: Column(
         crossAxisAlignment: CrossAxisAlignment.start,
         mainAxisSize: MainAxisSize.min,
@@ -22,14 +27,14 @@ class MapPopup extends StatelessWidget {
             children: [
               Icon(Icons.home_outlined),
               Padding(padding: EdgeInsets.only(left: 8)),
-              Text(station.town.isEmpty ? '-' : station.town),
+              Text(_station.town.isEmpty ? '-' : _station.town),
             ],
           ),
           Row(
             children: [
               Icon(Icons.water),
               Padding(padding: EdgeInsets.only(left: 8)),
-              Text(station.riverName.isEmpty ? '-' : station.riverName),
+              Text(_station.riverName.isEmpty ? '-' : _station.riverName),
             ],
           ),
           Row(
@@ -37,8 +42,8 @@ class MapPopup extends StatelessWidget {
               Icon(Icons.calendar_month_outlined),
               Padding(padding: EdgeInsets.only(left: 8)),
               Text(
-                station.dateOpened != null
-                    ? intl.DateFormat.yMd().format(station.dateOpened!)
+                _station.dateOpened != null
+                    ? intl.DateFormat.yMd().format(_station.dateOpened!)
                     : '-',
               ),
             ],
@@ -51,7 +56,7 @@ class MapPopup extends StatelessWidget {
           child: Text('dismiss'),
         ),
         TextButton(
-          onPressed: onShowTapped,
+          onPressed: _onShowTapped,
           child: Text('show'),
         ),
       ],