setState not updating the value in the screen using Flutter desktop - flutter

Question

So I'm trying to update the value of the drop down list using the setState, but when I select a value from the list, the value on the screen won't be able to change
import 'package:demo_app_admin/Custom/custom_Font.dart';
import 'package:flutter/material.dart';
import '/Custom/Custom_Raised_Bottun.dart';
import '/Custom/Header.dart';
import '/Custom/inputField.dart';
class LoginView extends StatefulWidget {
#override
_LoginViewState createState() => _LoginViewState();
}
class _LoginViewState extends State<LoginView> {
#override
Widget build(BuildContext context) {
final GlobalKey<FormState> _formKey = GlobalKey<FormState>();
final isKeyboard = MediaQuery.of(context).viewInsets.bottom != 0;
String _dropdownvalue = "Global admin";
List<String> _items = <String> ["Global admin", "Institution admin"];
return Scaffold(
body: Container(
width: double.infinity,
decoration: BoxDecoration(
gradient: LinearGradient(begin: Alignment.topCenter, colors: [
Colors.teal[700]!,
Colors.teal[200]!,
Colors.teal[400]!
]),
),
child: Column(
children: <Widget>[
const SizedBox(
height: 80,
),
if (!isKeyboard)
Header(
padding: const EdgeInsets.all(20),
crossAxisAlignment: CrossAxisAlignment.start,
head: "Welcome",
headTextStyle:
const TextStyle(color: Colors.white, fontSize: 40),
sizedBoxHeight: 10,
subtitle: "Sign In to Your Admin Account",
subtitleTextStyle:
const TextStyle(color: Colors.white, fontSize: 18),
),
Expanded(
child: Container(
decoration: const BoxDecoration(
color: Colors.white,
borderRadius: BorderRadius.only(
topLeft: Radius.circular(60),
topRight: Radius.circular(60),
)),
child: Padding(
padding: const EdgeInsets.all(30),
child: SingleChildScrollView(
reverse: true,
padding: EdgeInsets.all(32),
child: Form(
key: _formKey,
child: Column(
children: <Widget>[
const SizedBox(
height: 40,
),
Container(
decoration: BoxDecoration(
color: Colors.white,
borderRadius: BorderRadius.circular(10)),
child: Column(
children: <Widget>[
InputField(
labelText: 'Email',
padding: EdgeInsets.all(10),
borderSide: BorderSide(color: Colors.grey),
hintText: "Enter your email",
color: Colors.grey,
inputBorder: InputBorder.none,
obscureText: false,
enableSuggestion: true,
autoCorrect: true,
onSaved: (value) {},
// (value){controller.email = value!;},
validator: (value) {
if (value == null) {
print("ERROR");
}
},
),
InputField(
labelText: 'Password',
padding: EdgeInsets.all(10),
borderSide: BorderSide(color: Colors.grey),
hintText: "Enter your password",
color: Colors.grey,
inputBorder: InputBorder.none,
obscureText: true,
enableSuggestion: false,
autoCorrect: false,
onSaved: (value) {},
// (value){ controller.password = value!;},
validator: (value) {
if (value == null) {
print("ERROR");
}
},
),
],
),
),
const SizedBox(
height: 40,
),
here is the issue
DropdownButton<String>(
value: _dropdownvalue,
icon: Icon(Icons.keyboard_arrow_down),
items: _items.map((String _items) {
return DropdownMenuItem<String>(
value: _items,
child: CustomFont(text: _items),
);
}).toList(),
onChanged: (value) {
setState(() => _dropdownvalue = value!);
}),
const SizedBox(
height: 40,
),
CustomRaisedButton(
width: 200,
height: 50.0,
margin: const EdgeInsets.symmetric(horizontal: 50),
color: Colors.teal.shade500,
borderRadius: BorderRadius.circular(10),
text: "LOGIN",
textColor: Colors.white,
fontSize: 17,
fontWeight: FontWeight.bold,
function: () {}
// {
// _formKey.currentState?.save();
// if(_formKey.currentState?.validate() !=null){
// controller.signInWithEmailAndPassword();
// }
// },
),
SizedBox(
height: 10,
),
],
),
),
),
),
))
],
),
),
);
}
}

Answer 1

The issue is here, you are declaring variables inside build. Therefore, variables get reset to default value on every build. Means setState.
Declare variables outside the build method.
class _LoginViewState extends State<LoginView> {
final GlobalKey<FormState> _formKey = GlobalKey<FormState>();
String _dropdownvalue = "Global admin";
List<String> _items = <String>["Global admin", "Institution admin"];
#override
Widget build(BuildContext context) {
final isKeyboard = MediaQuery.of(context).viewInsets.bottom != 0;
return Scaffold(
More about StatefulWidget.