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,
                            ),
                          ],
                        ),
                      ),
                    ),
                  ),
                ))
              ],
            ),
          ),
        );
      }
    }

CodePudding user response：

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.