dynamically change google maps longitude and latitudes - flutter

Question

am new to flutter, and stuck logically on this problem :
i have a dropdown menu where the user will choose a gate from,
then show the chosen gate in the google map.
i've tried having the longitude and latitudes as global vairiables, but it didn't work . as if google map widget doesn't see it after it changes,
i also tried passing the longitude and latitudes using the navigator, with this the attributes does change in the google map but the dropdown menu stops showing the chosen item in the front.
i just want to change the google map depending on the choice of the dropdown menu.
heres my full code
import 'package:flutter/src/widgets/container.dart';
import 'package:flutter/src/widgets/framework.dart';
import 'package:flutter/material.dart';
import 'package:google_maps_flutter/google_maps_flutter.dart';
import '../widgets/My_wedgits.dart';
// shmalyh 3 LatLng(21.489191114466923, 39.24285294444855)
//shmalyh 1 LatLng( 21.490190928284374, 39.24029335794148)
//west 2 LatLng(21.489312801215913, 39.239637004938416)
//double lat = 21.48880614639443;
//double leng = 39.24159501940586;
String dropdownvalue = "";
const List<String> gatelist = <String>[
'NorthGate 1',
'NorthGate 3',
'WestGate 2'
];
class homepage extends StatefulWidget {
//const homepage({super.key});
double lat;
double lan;
homepage({Key? mykey, required this.lan, required this.lat})
: super(key: mykey);
#override
State<homepage> createState() => _homepageState();
}
class _homepageState extends State<homepage> {
DropdownButtonExample mydropdown = DropdownButtonExample();
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
toolbarHeight: 60,
centerTitle: true,
title: const Text(
'Wajeeh',
style: TextStyle(
fontSize: 28,
),
),
elevation: 10,
backgroundColor: const Color.fromARGB(255, 4, 105, 55),
leading: Padding(
padding: const EdgeInsets.all(6.0),
child: Image.asset(
'images/logo2.png',
height: 30,
),
),
),
backgroundColor: Colors.white,
body: Column(
children: [
const SizedBox(
height: 70,
),
Row(
// ignore: prefer_const_literals_to_create_immutables
children: [
Expanded(
child: Align(
alignment: Alignment.topCenter,
child: SizedBox(
width: 250,
child: mydropdown,
),
)),
],
),
const SizedBox(
height: 45,
),
Row(
children: [
Expanded(
child: Column(
children: [
Image.asset('images/full.jpg'),
const Text(
'Total Parking',
style: TextStyle(
fontSize: 22.0,
fontWeight: FontWeight.bold,
color: Color.fromARGB(255, 0, 0, 0)),
),
const Text(
'33',
style: TextStyle(
fontSize: 22.0,
fontWeight: FontWeight.bold,
color: Color.fromARGB(255, 4, 105, 55)),
),
],
)),
Expanded(
child: Column(
children: [
Image.asset('images/remain.jpg'),
const Text(
'Available Parking',
style: TextStyle(
fontSize: 22.0,
fontWeight: FontWeight.bold,
color: Color.fromARGB(255, 0, 0, 0)),
),
const Text(
"100",
style: TextStyle(
fontSize: 22.0,
fontWeight: FontWeight.bold,
color: Color.fromARGB(255, 4, 105, 55)),
),
],
))
],
),
//here where the map should be
const SizedBox(
height: 70,
),
Row(
// ignore: prefer_const_literals_to_create_immutables
children: [
Expanded(
child: Align(
alignment: Alignment.topCenter,
child: SizedBox(
width: 355,
height: 315,
child: Stack(
children: [
GoogleMap(
initialCameraPosition: CameraPosition(
target: LatLng(widget.lan, widget.lat),
zoom: 16,
),
),
Container(
alignment: Alignment.topLeft,
child: const Icon(
Icons.star,
color: Color.fromARGB(255, 231, 210, 23),
size: 40,
),
),
],
),
),
)),
],
),
],
));
}
// ignore: unused_element
}
class DropdownButtonExample extends StatefulWidget {
const DropdownButtonExample({super.key});
#override
State<DropdownButtonExample> createState() => _DropdownButtonExampleState();
/*Widget goodglemap() {
return GoogleMap(
initialCameraPosition: CameraPosition(
target: LatLng(lat, leng),
zoom: 16,
),
);
}*/
}
class _DropdownButtonExampleState extends State<DropdownButtonExample> {
double lat = 21.48880614639443;
double leng = 39.24159501940586;
String dropdownValue = gatelist.first;
// ignore: avoid_print
#override
Widget build(BuildContext context) {
return DropdownButton<String>(
hint: const Text("Choose a Gate"),
isExpanded: true,
value: dropdownValue,
icon: const Icon(Icons.arrow_drop_down_sharp),
style: const TextStyle(color: const Color.fromARGB(255, 4, 105, 55)),
underline: Container(
height: 2,
color: const Color.fromARGB(255, 4, 105, 55),
),
onChanged: (String? value) {
// This is called when the user selects an item.
setState(() {
dropdownValue = value!;
//see if i can reach the other classs from here
if (identical(dropdownValue, "NorthGate 1")) {
lat = 21.490190928284374;
leng = 39.24029335794148;
}
//see if i can reach the other classs from here
if (identical(dropdownValue, "NorthGate 3")) {
lat = 21.489191114466923;
leng = 39.24285294444855;
}
if (identical(dropdownValue, "WestGate 2")) {
lat = 21.489312801215913;
leng = 39.239637004938416;
}
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => homepage(lat: lat, lan: leng)));
});
},
items: gatelist.map<DropdownMenuItem<String>>((String value) {
return DropdownMenuItem<String>(
value: value,
child: Text(
value,
),
);
}).toList(),
);
}
Widget goodglemap() {
return GoogleMap(
initialCameraPosition: CameraPosition(
target: LatLng(lat, leng),
zoom: 16,
),
);
}
}