Why i am not able to use setState Under GestureDetector - flutter

Question

Why I am not able to use setState Under GestureDetector Using onTap:
After I use setState I got an error like: The function 'setState' isn't defined.
Try importing the library that defines 'setState', And VS Code editor show me
Error like: correcting the name to the name of an existing function, or defining a function named 'setState'.dart(undefined_function).
I try to fix different ways please tell me where is my problem
Thank you
Some Flutter Import Link ::::::::::
class ParsingMap extends StatefulWidget {
const ParsingMap({Key? key}) : super(key: key);
#override
_ParsingMapState createState() => _ParsingMapState();
}
class _ParsingMapState extends State<ParsingMap> {
Future<ApiList>? data;
#override
void initState() {
super.initState();
Network network = Network("https://fakestoreapi.com/products");
data = network.loadPosts();
// print(data);
setState(() {});
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
backgroundColor: Colors.white,
elevation: 0,
leading: Icon(Icons.arrow_left, color: Colors.black),
actions: [
Icon(Icons.search, color: Colors.black),
SizedBox(width: 10),
Icon(Icons.home_filled, color: Colors.black),
SizedBox(width: 8)
],
),
body: Center(
child: Container(
child: FutureBuilder(
future: data,
builder: (context, AsyncSnapshot<ApiList> snapshot) {
List<Api> allPosts;
if (snapshot.hasData) {
allPosts = snapshot.data!.apis!;
return createListView(allPosts, context);
}
return CircularProgressIndicator();
},
),
),
),
);
}
}
class Network {
final String url;
Network(this.url);
Future<ApiList> loadPosts() async {
final response = await get(Uri.parse(url));
if (response.statusCode == 200) {
// print(response.body);
return ApiList.fromJson(json.decode(response.body));
} else {
throw Exception("Faild To get posts");
}
}
}
Widget createListView(List<Api> data, BuildContext context) {
return ListView(
children: [
Container(
height: 300,
margin: EdgeInsets.symmetric(vertical: 16),
child: ListView.builder(
itemCount: data.length,
scrollDirection: Axis.horizontal,
physics: BouncingScrollPhysics(),
padding: EdgeInsets.symmetric(horizontal: 16),
itemBuilder: (context, index) {
int selectedIndex = 0;
return GestureDetector(
onTap: () {
setState(() {
selectedIndex = index;
});
},
child: Padding(
padding: const EdgeInsets.symmetric(horizontal: 10),
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
Text(
"${data[index].category}",
style: TextStyle(
fontWeight: FontWeight.bold,
color: selectedIndex == index
? Colors.black
: Colors.black38),
),
Container(
margin: EdgeInsets.only(
top: 5,
),
height: 2,
width: 30,
color: selectedIndex == index
? Colors.black
: Colors.transparent,
)
],
),
),
);
},
),
),
],
);
}

Answer 1

Put top-level createListView function in _ParsingMapState class.
class _ParsingMapState extends State<ParsingMap> {
// ...
Widget createListView(...) {}
}