The border does not change to red on validation error about dropdown_button2

[yashanghan22]

@nelci592 , I think your validation is returning null every time. Try removing your validation and returning a simple string instead to see if it works.

[nelci592]

@yashanghan22 I have tested on this sample project, however, on error, the underline's color remains the same:

import 'package:dropdown_example/dropdown/dropdown_button2.dart';
import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: 'DropdownButton2 Demo',
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key});

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  final List<String> items = [
    'Item1',
    'Item2',
    'Item3',
    'Item4',
    'Item5',
    'Item6',
    'Item7',
    'Item8'
  ];
  final valueListenable = ValueNotifier<String?>(null);
  AutovalidateMode _autoValidateMode = AutovalidateMode.disabled;
  final GlobalKey<FormState> _formKey = GlobalKey();

  @override
  void initState() {
    _autoValidateMode = AutovalidateMode.onUserInteraction;

    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(mainAxisAlignment: MainAxisAlignment.center, children: [
          Form(
            key: _formKey,
            child: SizedBox(
              width: 400,
              child: DropdownButtonFormField2<String>(
                autovalidateMode: _autoValidateMode,
                isExpanded: true,
                hint: const Row(
                  children: [
                    Icon(
                      Icons.list,
                      size: 16,
                      color: Colors.yellow,
                    ),
                    SizedBox(
                      width: 4,
                    ),
                    Expanded(
                      child: Text(
                        'Select Item',
                        style: TextStyle(
                          fontSize: 14,
                          fontWeight: FontWeight.bold,
                          color: Colors.yellow,
                        ),
                        overflow: TextOverflow.ellipsis,
                      ),
                    ),
                  ],
                ),
                items: items
                    .map((String item) => DropdownItem<String>(
                          value: item,
                          height: 40,
                          child: Text(
                            item,
                            style: const TextStyle(
                              fontSize: 14,
                              fontWeight: FontWeight.bold,
                              color: Colors.white,
                            ),
                            overflow: TextOverflow.ellipsis,
                          ),
                        ))
                    .toList(),
                valueListenable: valueListenable,
                validator: (value) {
                  if (value == null || value.isEmpty) {
                    return 'Please select an option';
                  }
                  return null;
                },
                onChanged: (value) {
                  valueListenable.value = value;
                },
                decoration: const InputDecoration(
                  labelText: "Text ",
                  floatingLabelBehavior: FloatingLabelBehavior.auto,
                  labelStyle: TextStyle(
                    color: Color(0xFF7F849D),
                    fontSize: 15,
                    height: 0.3,
                  ),
                  errorBorder: UnderlineInputBorder(
                      borderRadius: BorderRadius.all(Radius.circular(1)),
                      borderSide: BorderSide(color: Colors.red, width: 1)),
                  focusedBorder: UnderlineInputBorder(
                      borderRadius: BorderRadius.all(Radius.circular(1)),
                      borderSide:
                          BorderSide(color: Color(0xFF2A2C42), width: 1)),
                  border: UnderlineInputBorder(
                      borderRadius: BorderRadius.all(Radius.circular(1)),
                      borderSide:
                          BorderSide(color: Color(0xFF2A2C42), width: 1)),
                  enabledBorder: UnderlineInputBorder(
                      borderRadius: BorderRadius.all(Radius.circular(1)),
                      borderSide:
                          BorderSide(color: Color(0xFF2A2C42), width: 1)),
                  isDense: true,
                  hintStyle: TextStyle(
                    color: Color(0xFF7F849D),
                    fontSize: 15,
                  ),
                ),
                buttonStyleData: const ButtonStyleData(
                  height: 50,
                  width: 160,
                  padding: EdgeInsets.only(left: 14, right: 14),
                  elevation: 2,
                ),
                iconStyleData: const IconStyleData(
                  icon: Icon(
                    Icons.arrow_forward_ios_outlined,
                  ),
                  iconSize: 14,
                  iconEnabledColor: Colors.yellow,
                  iconDisabledColor: Colors.grey,
                ),
                dropdownStyleData: DropdownStyleData(
                  maxHeight: 200,
                  width: 200,
                  decoration: BoxDecoration(
                    borderRadius: BorderRadius.circular(14),
                    color: Colors.grey,
                  ),
                  offset: const Offset(-20, 0),
                  scrollbarTheme: ScrollbarThemeData(
                    radius: const Radius.circular(40),
                    thickness: MaterialStateProperty.all<double>(6),
                    thumbVisibility: MaterialStateProperty.all<bool>(true),
                  ),
                ),
                menuItemStyleData: const MenuItemStyleData(
                  padding: EdgeInsets.only(left: 14, right: 14),
                ),
              ),
            ),
          ),
          Padding(
            padding: const EdgeInsets.only(top: 50),
            child: TextButton(
                onPressed: () {
                  _formKey.currentState?.validate();
                },
                child: const Text("Validate")),
          )
        ]),
      ),
    );
  }
}

[yashanghan22]

Can you change the color of all the underlined borders to blue, black, or grey? Do not change the error border color.

Then see if it's work or not because you are giving light red color to focused border, border, enabled border so it might be showing like same colour as error border colour.

[nelci592]

I have already tested this but it does not seem to work. You can check the sample project that I attached.
dropdown_example.zip

[yashanghan22]

@nelci592
Let me know if it's the solution of your problem

dropdown.error.border.issue.webm

solution:
In the input decoration, there is a parameter called errorText, which is a string that can be empty (nullable). By default, its value is null (empty).

• If errorText is not null (has some text), the inputDecoration will show an error border.
• If errorText is null (empty), the inputDecoration will show a regular border.

I created a variable that will show an error based on validation. For more details, please check the updated code file.

Here is the project with updated code:
dropdown_example.zip

let me know if there is an issue in this code.