dropdown_button2

Flutter's core Dropdown Button widget with steady dropdown menu and many options you can customize to your needs.


Keywords
android, button, custom-widget, dart, dart-package, dropdown, dropdownbutton, flutter, widget
License
MIT

Documentation

Flutter DropdownButton2

Pub Version Flutter Version License: MIT Build Status

Intro

Flutter's core Dropdown Button widget with steady dropdown menu and many other options you can customize to your needs.

Image

Features

  • Dropdown menu always open below the button "as long as it's possible otherwise it'll open to the end of the screen" and you can edit its position by using the offset parameter.
  • You can control how (button, button's icon, dropdown menu and menu items) will be displayed "read Options below".
  • You can align (hint & value) and customize them.
  • You can edit the scrollbar's radius,thickness and isAlwaysShow.
  • You can set max height for the dropdown menu & it'll become scrollable if there are more items.
  • If you pass Null to dropdownMaxHeight parameter or didn't use it, the dropdown menu will take max height possible for the items and will become scrollable if there are more items.
  • If you have long scrollable list, the dropdown menu will auto scroll to current selected item and show it at the middle of the menu if possible.
  • Wrap DropdownButton2 with DropdownButtonHideUnderline to hide the underline.
  • A Custom widget of the DropdownButton2 below to make it more reusable. You can customize it to your needs and use it throughout all your app easily as shown in the examples.
  • You can use DropdownButton2 with items of different heights like dividers as shown in the examples.
  • You can use DropdownButton2 as Multiselect Dropdown with Checkboxes as shown in the examples.
  • You can use DropdownButton2 as Searchable Dropdown as shown in the examples.
  • You can use DropdownButton2 as a popup menu button by using the parameter customButton. You can pass Icon,Image or any widget and customize it as shown in the examples.
  • You can also use DropdownButtonFormField2 the same way with all options above and use it inside Form as shown in the examples.
  • Use decoration parameter for the DropdownButtonFormField2 to add borders, label and more.
  • You can customize DropdownButtonFormField2 width by wrapping it with Padding or with SizedBox and give it the width you want.

Options

DropdownButton2:

Option Description Type Required
items The list of items the user can select List<DropdownItem> Yes
selectedItemBuilder A builder to customize how the selected item will be displayed on the button DropdownButtonBuilder No
valueListenable A [ValueListenable] that represents the value of the currently selected [DropdownItem]. ValueListenable<T?>? No
multiValueListenable A [ValueListenable] that represents a list of the currently selected [DropdownItem]s ValueListenable<List<T>>? No
hint The placeholder displayed before the user choose an item Widget No
disabledHint The placeholder displayed if the dropdown is disabled Widget No
onChanged Called when the user selects an item ValueChanged<T?> No
onMenuStateChange Called when the dropdown menu opens or closes OnMenuStateChangeFn No
style The text style to use for text in the dropdown button and the dropdown menu TextStyle No
underline The widget to use for drawing the drop-down button's underline Widget No
isDense Reduce the button's height bool No
isExpanded Makes the button's inner contents expanded (set true to avoid long text overflowing) bool No
alignment Defines how the hint or the selected item is positioned within the button AlignmentGeometry No
buttonStyleData Used to configure the theme of the button ButtonStyleData No
iconStyleData Used to configure the theme of the button's icon IconStyleData No
dropdownStyleData Used to configure the theme of the dropdown menu DropdownStyleData No
menuItemStyleData Used to configure the theme of the dropdown menu items MenuItemStyleData No
dropdownSearchData Used to configure searchable dropdowns DropdownSearchData No
dropdownSeparator Adds separator widget to the dropdown menu DropdownSeparator No
customButton Uses custom widget like icon,image,etc.. instead of the default button Widget No
openWithLongPress Opens the dropdown menu on long-pressing instead of tapping bool No
barrierDismissible Whether you can dismiss this route by tapping the modal barrier bool No
barrierColor The color to use for the modal barrier. If this is null, the barrier will be transparent Color No
barrierLabel The semantic label used for a dismissible barrier String No
barrierCoversButton Specifies whether the modal barrier should cover the dropdown button or not. bool No
openDropdownListenable A [Listenable] that can be used to programmatically open the dropdown menu. Listenable? No

Subclass ButtonStyleData:

Option Description Type Required
height The height of the button double No
width The width of the button double No
padding The inner padding of the Button EdgeInsetsGeometry No
decoration The decoration of the Button BoxDecoration No
elevation The elevation of the Button int No
overlayColor Defines the ink response focus, hover, and splash colors for the button MaterialStateProperty<Color?> No

Subclass IconStyleData:

Option Description Type Required
icon The widget to use for the drop-down button's suffix icon Widget No
iconDisabledColor The color of the icon if the button is disabled Color No
iconEnabledColor The color of the icon if the button is enabled Color No
iconSize The size of the icon double No
openMenuIcon Shows different icon when dropdown menu is open Widget No

Subclass DropdownStyleData:

Option Description Type Required
maxHeight The maximum height of the dropdown menu double No
width The width of the dropdown menu double No
padding The inner padding of the dropdown menu EdgeInsetsGeometry No
scrollPadding The inner padding of the dropdown menu including the scrollbar EdgeInsetsGeometry No
decoration The decoration of the dropdown menu BoxDecoration No
elevation The elevation of the dropdown menu int No
direction The direction of the dropdown menu in relation to the button DropdownDirection No
offset Changes the position of the dropdown menu Offset No
isOverButton Opens the dropdown menu over the button instead of below it bool No
useSafeArea Determine if the dropdown menu should only display in safe areas of the screen bool No
useRootNavigator Determine whether to open the dropdown menu using the root Navigator or not bool No
scrollbarTheme Configures the theme of the menu's scrollbar ScrollbarThemeData No
openInterval The animation curve used for opening the dropdown menu (forward direction) Interval No
dropdownBuilder A builder to customize the dropdown menu DropdownBuilder No

Subclass MenuItemStyleData:

Option Description Type Required
padding The padding of menu items EdgeInsetsGeometry No
borderRadius The border radius of the menu item BorderRadius No
overlayColor Defines the ink response focus, hover, and splash colors for the items MaterialStateProperty<Color?> No
selectedMenuItemBuilder A builder to customize the selected menu item SelectedMenuItemBuilder No

Subclass DropdownSearchData:

Option Description Type Required
searchController The controller used for searchable dropdowns, if null, then it'll perform as a normal dropdown TextEditingController No
searchBarWidget The widget to be shown at the top of the dropdown menu for searchable dropdowns Widget No
searchBarWidgetHeight The height of the searchBarWidget if used double No
noResultsWidget The widget to show when the search results are empty Widget No
searchMatchFn The match function used for searchable dropdowns, if null, defaultFn will be used SearchMatchFn No

DropdownButtonFormField2 (In addition to the above):

Option Description Type Required
decoration The decoration of the dropdown button form field InputDecoration No
onSaved Called with the current selected item when the form is saved FormFieldSetter No
validator Called to validates if the input is invalid and display error text FormFieldValidator No
autovalidateMode Used to enable/disable auto validation AutovalidateMode No

Installation

add this line to pubspec.yaml

dependencies:
  dropdown_button2: ^3.0.0-beta.19

import package

import 'package:dropdown_button2/dropdown_button2.dart';

Usage and Examples

1. Simple DropdownButton2 with no styling:

Image

final List<String> items = [
  'Item1',
  'Item2',
  'Item3',
  'Item4',
];
final valueListenable = ValueNotifier<String?>(null);

@override
Widget build(BuildContext context) {
  return Scaffold(
    body: Center(
      child: DropdownButtonHideUnderline(
        child: DropdownButton2<String>(
          isExpanded: true,
          hint: Text(
            'Select Item',
            style: TextStyle(
              fontSize: 14,
              color: Theme.of(context).hintColor,
            ),
          ),
          items: items
              .map((String item) => DropdownItem<String>(
                    value: item,
                    height: 40,
                    child: Text(
                      item,
                      style: const TextStyle(
                        fontSize: 14,
                      ),
                    ),
                  ))
              .toList(),
          valueListenable: valueListenable,
          onChanged: (String? value) {
            valueListenable.value = value;
          },
          buttonStyleData: const ButtonStyleData(
            padding: EdgeInsets.symmetric(horizontal: 16),
            height: 40,
            width: 140,
          ),
        ),
      ),
    ),
  );
}

2. DropdownButton2 with few styling and customization:

Image

final List<String> items = [
  'Item1',
  'Item2',
  'Item3',
  'Item4',
  'Item5',
  'Item6',
  'Item7',
  'Item8',
];
final valueListenable = ValueNotifier<String?>(null);

@override
Widget build(BuildContext context) {
  return Scaffold(
    body: Center(
      child: DropdownButtonHideUnderline(
        child: DropdownButton2<String>(
          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,
          onChanged: (value) {
            valueListenable.value = value;
          },
          buttonStyleData: ButtonStyleData(
            height: 50,
            width: 160,
            padding: const EdgeInsets.only(left: 14, right: 14),
            decoration: BoxDecoration(
              borderRadius: BorderRadius.circular(14),
              border: Border.all(
                color: Colors.black26,
              ),
              color: Colors.redAccent,
            ),
            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.redAccent,
            ),
            offset: const Offset(-20, 0),
            scrollbarTheme: ScrollbarThemeData(
              radius: const Radius.circular(40),
              thickness: MaterialStateProperty.all(6),
              thumbVisibility: MaterialStateProperty.all(true),
            ),
          ),
          menuItemStyleData: const MenuItemStyleData(
            padding: EdgeInsets.only(left: 14, right: 14),
          ),
        ),
      ),
    ),
  );
}

3. DropdownButton2 with separator widgets like dividers:

Image

final List<String> items = [
  'Item1',
  'Item2',
  'Item3',
  'Item4',
];
final valueListenable = ValueNotifier<String?>(null);

@override
Widget build(BuildContext context) {
  return Scaffold(
    body: Center(
      child: DropdownButtonHideUnderline(
        child: DropdownButton2<String>(
          isExpanded: true,
          hint: Text(
            'Select Item',
            style: TextStyle(
              fontSize: 14,
              color: Theme.of(context).hintColor,
            ),
          ),
          items: items
              .map((String item) => DropdownItem<String>(
                    value: item,
                    height: 40,
                    child: Padding(
                      padding: const EdgeInsets.symmetric(horizontal: 8.0),
                      child: Text(
                        item,
                        style: const TextStyle(
                          fontSize: 14,
                        ),
                      ),
                    ),
                  ))
              .toList(),
          dropdownSeparator: const DropdownSeparator(
            height: 4,
            child: Padding(
              padding: EdgeInsets.symmetric(horizontal: 8.0),
              child: Divider(),
            ),
          ),
          valueListenable: valueListenable,
          onChanged: (value) {
            valueListenable.value = value;
          },
          buttonStyleData: const ButtonStyleData(
            padding: EdgeInsets.symmetric(horizontal: 16),
            height: 40,
            width: 140,
          ),
          dropdownStyleData: const DropdownStyleData(
            maxHeight: 200,
          ),
          menuItemStyleData: const MenuItemStyleData(
            padding: EdgeInsets.symmetric(horizontal: 8.0),
          ),
          iconStyleData: const IconStyleData(
            openMenuIcon: Icon(Icons.arrow_drop_up),
          ),
        ),
      ),
    ),
  );
}

4. DropdownButton2 as Multiselect Dropdown with Checkboxes:

Image

final List<String> items = [
  'All',
  'Item1',
  'Item2',
  'Item3',
  'Item4',
];
final multiValueListenable = ValueNotifier<List<String>>([]);

@override
Widget build(BuildContext context) {
  return Scaffold(
    body: Center(
      child: DropdownButtonHideUnderline(
        child: DropdownButton2<String>(
          isExpanded: true,
          hint: Text(
            'Select Items',
            style: TextStyle(
              fontSize: 14,
              color: Theme.of(context).hintColor,
            ),
          ),
          items: items.map((item) {
            return DropdownItem(
              value: item,
              height: 40,
              closeOnTap: false,
              child: ValueListenableBuilder<List<String>>(
                valueListenable: multiValueListenable,
                builder: (context, multiValue, _) {
                  final isSelected = multiValue.contains(item);
                  return Container(
                    height: double.infinity,
                    padding: const EdgeInsets.symmetric(horizontal: 16.0),
                    child: Row(
                      children: [
                        if (isSelected)
                          const Icon(Icons.check_box_outlined)
                        else
                          const Icon(Icons.check_box_outline_blank),
                        const SizedBox(width: 16),
                        Expanded(
                          child: Text(
                            item,
                            style: const TextStyle(
                              fontSize: 14,
                            ),
                          ),
                        ),
                      ],
                    ),
                  );
                },
              ),
            );
          }).toList(),
          multiValueListenable: multiValueListenable,
          onChanged: (value) {
            final multiValue = multiValueListenable.value;
            final isSelected = multiValue.contains(value);
            if (value == 'All') {
              isSelected
                  ? multiValueListenable.value = []
                  : multiValueListenable.value = List.from(items);
            } else {
              multiValueListenable.value = isSelected
                  ? ([...multiValue]..remove(value))
                  : [...multiValue, value!];
            }
          },
          selectedItemBuilder: (context) {
            return items.map(
              (item) {
                return ValueListenableBuilder<List<String>>(
                    valueListenable: multiValueListenable,
                    builder: (context, multiValue, _) {
                      return Container(
                        alignment: AlignmentDirectional.center,
                        child: Text(
                          multiValue
                              .where((item) => item != 'All')
                              .join(', '),
                          style: const TextStyle(
                            fontSize: 14,
                            overflow: TextOverflow.ellipsis,
                          ),
                          maxLines: 1,
                        ),
                      );
                    });
              },
            ).toList();
          },
          buttonStyleData: const ButtonStyleData(
            padding: EdgeInsets.only(left: 16, right: 8),
            height: 40,
            width: 140,
          ),
          menuItemStyleData: const MenuItemStyleData(
            padding: EdgeInsets.zero,
          ),
        ),
      ),
    ),
  );
}

5. DropdownButton2 as Searchable Dropdown:

Image

final List<String> items = [
  'A_Item1',
  'A_Item2',
  'A_Item3',
  'A_Item4',
  'B_Item1',
  'B_Item2',
  'B_Item3',
  'B_Item4',
];

final valueListenable = ValueNotifier<String?>(null);
final TextEditingController textEditingController = TextEditingController();

@override
void dispose() {
  textEditingController.dispose();
  super.dispose();
}

@override
Widget build(BuildContext context) {
  return Scaffold(
    body: Center(
      child: DropdownButtonHideUnderline(
        child: DropdownButton2<String>(
          isExpanded: true,
          hint: Text(
            'Select Item',
            style: TextStyle(
              fontSize: 14,
              color: Theme.of(context).hintColor,
            ),
          ),
          items: items
              .map((item) => DropdownItem(
                    value: item,
                    height: 40,
                    child: Text(
                      item,
                      style: const TextStyle(
                        fontSize: 14,
                      ),
                    ),
                  ))
              .toList(),
          valueListenable: valueListenable,
          onChanged: (value) {
            valueListenable.value = value;
          },
          buttonStyleData: const ButtonStyleData(
            padding: EdgeInsets.symmetric(horizontal: 16),
            height: 40,
            width: 200,
          ),
          dropdownStyleData: const DropdownStyleData(
            maxHeight: 200,
          ),
          dropdownSearchData: DropdownSearchData(
            searchController: textEditingController,
            searchBarWidgetHeight: 50,
            searchBarWidget: Container(
              height: 50,
              padding: const EdgeInsets.only(
                top: 8,
                bottom: 4,
                right: 8,
                left: 8,
              ),
              child: TextFormField(
                expands: true,
                maxLines: null,
                controller: textEditingController,
                decoration: InputDecoration(
                  isDense: true,
                  contentPadding: const EdgeInsets.symmetric(
                    horizontal: 10,
                    vertical: 8,
                  ),
                  hintText: 'Search for an item...',
                  hintStyle: const TextStyle(fontSize: 12),
                  border: OutlineInputBorder(
                    borderRadius: BorderRadius.circular(8),
                  ),
                ),
              ),
            ),
            noResultsWidget: const Padding(
              padding: EdgeInsets.all(8),
              child: Text('No Item Found!'),
            ),
            searchMatchFn: (item, searchValue) {
              return item.value.toString().contains(searchValue);
            },
          ),
          //This to clear the search value when you close the menu
          onMenuStateChange: (isOpen) {
            if (!isOpen) {
              textEditingController.clear();
            }
          },
        ),
      ),
    ),
  );
}

6. DropdownButton2 as Popup menu button using customButton parameter:

Example 1 using icon:

Image

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

  @override
  State<PopupIconExample> createState() => _PopupIconExampleState();
}

class _PopupIconExampleState extends State<PopupIconExample> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: DropdownButtonHideUnderline(
          child: DropdownButton2(
            customButton: const Icon(
              Icons.list,
              size: 46,
              color: Colors.red,
            ),
            items: [
              ..._MenuItems.firstItems.map(
                (item) => DropdownItem<_MenuItem>(
                  value: item,
                  height: 48,
                  child: _MenuItems.buildItem(item),
                ),
              ),
              const DropdownItem<Divider>(
                enabled: false,
                height: 8,
                child: Divider(),
              ),
              ..._MenuItems.secondItems.map(
                (item) => DropdownItem<_MenuItem>(
                  value: item,
                  height: 48,
                  child: _MenuItems.buildItem(item),
                ),
              ),
            ],
            onChanged: (value) {
              _MenuItems.onChanged(context, value! as _MenuItem);
            },
            dropdownStyleData: DropdownStyleData(
              width: 160,
              padding: const EdgeInsets.symmetric(vertical: 6),
              decoration: BoxDecoration(
                borderRadius: BorderRadius.circular(4),
                color: Colors.redAccent,
              ),
              offset: const Offset(0, 8),
            ),
            menuItemStyleData: const MenuItemStyleData(
              padding: EdgeInsets.only(left: 16, right: 16),
            ),
          ),
        ),
      ),
    );
  }
}

class _MenuItem {
  const _MenuItem({
    required this.text,
    required this.icon,
  });

  final String text;
  final IconData icon;
}

abstract class _MenuItems {
  static const List<_MenuItem> firstItems = [home, share, settings];
  static const List<_MenuItem> secondItems = [logout];

  static const home = _MenuItem(text: 'Home', icon: Icons.home);
  static const share = _MenuItem(text: 'Share', icon: Icons.share);
  static const settings = _MenuItem(text: 'Settings', icon: Icons.settings);
  static const logout = _MenuItem(text: 'Log Out', icon: Icons.logout);

  static Widget buildItem(_MenuItem item) {
    return Row(
      children: [
        Icon(item.icon, color: Colors.white, size: 22),
        const SizedBox(
          width: 10,
        ),
        Expanded(
          child: Text(
            item.text,
            style: const TextStyle(
              color: Colors.white,
            ),
          ),
        ),
      ],
    );
  }

  static void onChanged(BuildContext context, _MenuItem item) {
    switch (item) {
      case _MenuItems.home:
        //Do something
        break;
      case _MenuItems.settings:
        //Do something
        break;
      case _MenuItems.share:
        //Do something
        break;
      case _MenuItems.logout:
        //Do something
        break;
    }
  }
}

Example 2 using image and openWithLongPress parameter:

Image

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

  @override
  State<PopupImageExample> createState() => _PopupImageExampleState();
}

class _PopupImageExampleState extends State<PopupImageExample> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: DropdownButtonHideUnderline(
          child: DropdownButton2(
            customButton: Container(
              height: 240,
              width: 240,
              decoration: BoxDecoration(
                borderRadius: BorderRadius.circular(40),
                image: const DecorationImage(
                  image: AssetImage(
                    'assets/images/city.jpg',
                  ),
                  fit: BoxFit.cover,
                ),
              ),
            ),
            openWithLongPress: true,
            items: [
              ..._MenuItems.firstItems.map(
                (item) => DropdownItem<_MenuItem>(
                  value: item,
                  height: 48,
                  child: _MenuItems.buildItem(item),
                ),
              ),
              const DropdownItem<Divider>(
                enabled: false,
                height: 8,
                child: Divider(),
              ),
              ..._MenuItems.secondItems.map(
                (item) => DropdownItem<_MenuItem>(
                  value: item,
                  height: 48,
                  child: _MenuItems.buildItem(item),
                ),
              ),
            ],
            onChanged: (value) {
              _MenuItems.onChanged(context, value! as _MenuItem);
            },
            buttonStyleData: ButtonStyleData(
              // This is necessary for the ink response to match our customButton radius.
              decoration: BoxDecoration(
                borderRadius: BorderRadius.circular(40),
              ),
            ),
            dropdownStyleData: DropdownStyleData(
              width: 160,
              padding: const EdgeInsets.symmetric(vertical: 6),
              decoration: BoxDecoration(
                borderRadius: BorderRadius.circular(4),
                color: Colors.redAccent,
              ),
              offset: const Offset(40, -4),
            ),
            menuItemStyleData: const MenuItemStyleData(
              padding: EdgeInsets.only(left: 16, right: 16),
            ),
          ),
        ),
      ),
    );
  }
}

class _MenuItem {
  const _MenuItem({
    required this.text,
    required this.icon,
  });

  final String text;
  final IconData icon;
}

class _MenuItems {
  static const List<_MenuItem> firstItems = [like, share, download];
  static const List<_MenuItem> secondItems = [cancel];

  static const like = _MenuItem(text: 'Like', icon: Icons.favorite);
  static const share = _MenuItem(text: 'Share', icon: Icons.share);
  static const download = _MenuItem(text: 'Download', icon: Icons.download);
  static const cancel = _MenuItem(text: 'Cancel', icon: Icons.cancel);

  static Widget buildItem(_MenuItem item) {
    return Row(
      children: [
        Icon(
          item.icon,
          color: Colors.white,
          size: 22,
        ),
        const SizedBox(
          width: 10,
        ),
        Expanded(
          child: Text(
            item.text,
            style: const TextStyle(
              color: Colors.white,
            ),
          ),
        ),
      ],
    );
  }

  static void onChanged(BuildContext context, _MenuItem item) {
    switch (item) {
      case _MenuItems.like:
        //Do something
        break;
      case _MenuItems.share:
        //Do something
        break;
      case _MenuItems.download:
        //Do something
        break;
      case _MenuItems.cancel:
        //Do something
        break;
    }
  }
}

7. Using DropdownButtonFormField2 with Form:

Image

final List<String> genderItems = [
  'Male',
  'Female',
];
final valueListenable = ValueNotifier<String?>(null);

final _formKey = GlobalKey<FormState>();

@override
Widget build(BuildContext context) {
  return Scaffold(
    body: Form(
      key: _formKey,
      child: Padding(
        padding: const EdgeInsets.symmetric(horizontal: 80),
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            TextFormField(
              decoration: InputDecoration(
                contentPadding: const EdgeInsets.all(16),
                hintText: 'Enter Your Full Name.',
                hintStyle: const TextStyle(fontSize: 14),
                border: OutlineInputBorder(
                  borderRadius: BorderRadius.circular(15),
                ),
              ),
            ),
            const SizedBox(height: 30),
            DropdownButtonFormField2<String>(
              isExpanded: true,
              decoration: InputDecoration(
                // Add Horizontal padding using menuItemStyleData.padding so it matches
                // the menu padding when button's width is not specified.
                contentPadding: const EdgeInsets.symmetric(vertical: 16),
                border: OutlineInputBorder(
                  borderRadius: BorderRadius.circular(15),
                ),
                // Add more decoration..
              ),
              hint: const Text(
                'Select Your Gender',
                style: TextStyle(fontSize: 14),
              ),
              items: genderItems
                  .map((item) => DropdownItem<String>(
                        value: item,
                        child: Text(
                          item,
                          style: const TextStyle(
                            fontSize: 14,
                          ),
                        ),
                      ))
                  .toList(),
              valueListenable: valueListenable,
              validator: (value) {
                if (value == null) {
                  return 'Please select gender.';
                }
                return null;
              },
              onChanged: (value) {
                valueListenable.value = value;
              },
              iconStyleData: const IconStyleData(
                icon: Icon(
                  Icons.arrow_drop_down,
                  color: Colors.black45,
                ),
              ),
              dropdownStyleData: DropdownStyleData(
                decoration: BoxDecoration(
                  borderRadius: BorderRadius.circular(15),
                ),
              ),
              menuItemStyleData: const MenuItemStyleData(
                padding: EdgeInsets.symmetric(horizontal: 16),
              ),
            ),
            const SizedBox(height: 30),
            TextButton(
              onPressed: () {
                if (_formKey.currentState!.validate()) {
                  // Do something.
                }
              },
              child: const Text('Submit Button'),
            ),
          ],
        ),
      ),
    ),
  );
}

How to make a reusable DropdownButton2 for your app

class CustomDropdownButton2 extends StatelessWidget {
  const CustomDropdownButton2({
    required this.hint,
    required this.valueListenable,
    required this.dropdownItems,
    required this.onChanged,
    this.selectedItemBuilder,
    this.hintAlignment,
    this.valueAlignment,
    this.buttonHeight,
    this.buttonWidth,
    this.buttonPadding,
    this.buttonDecoration,
    this.buttonElevation,
    this.icon,
    this.iconSize,
    this.iconEnabledColor,
    this.iconDisabledColor,
    this.itemHeight,
    this.itemPadding,
    this.dropdownHeight,
    this.dropdownWidth,
    this.dropdownPadding,
    this.dropdownDecoration,
    this.dropdownElevation,
    this.scrollbarRadius,
    this.scrollbarThickness,
    this.scrollbarAlwaysShow,
    this.offset = Offset.zero,
    super.key,
  });
  final String hint;
  final ValueListenable<String?>? valueListenable;
  final List<String> dropdownItems;
  final ValueChanged<String?>? onChanged;
  final DropdownButtonBuilder? selectedItemBuilder;
  final Alignment? hintAlignment;
  final Alignment? valueAlignment;
  final double? buttonHeight, buttonWidth;
  final EdgeInsetsGeometry? buttonPadding;
  final BoxDecoration? buttonDecoration;
  final int? buttonElevation;
  final Widget? icon;
  final double? iconSize;
  final Color? iconEnabledColor;
  final Color? iconDisabledColor;
  final double? itemHeight;
  final EdgeInsetsGeometry? itemPadding;
  final double? dropdownHeight, dropdownWidth;
  final EdgeInsetsGeometry? dropdownPadding;
  final BoxDecoration? dropdownDecoration;
  final int? dropdownElevation;
  final Radius? scrollbarRadius;
  final double? scrollbarThickness;
  final bool? scrollbarAlwaysShow;
  final Offset offset;

  @override
  Widget build(BuildContext context) {
    return DropdownButtonHideUnderline(
      child: DropdownButton2<String>(
        //To avoid long text overflowing.
        isExpanded: true,
        hint: Container(
          alignment: hintAlignment,
          child: Text(
            hint,
            overflow: TextOverflow.ellipsis,
            maxLines: 1,
            style: TextStyle(
              fontSize: 14,
              color: Theme.of(context).hintColor,
            ),
          ),
        ),
        valueListenable: valueListenable,
        items: dropdownItems
            .map((String item) => DropdownItem<String>(
                  value: item,
                  height: itemHeight ?? 40,
                  child: Container(
                    alignment: valueAlignment,
                    child: Text(
                      item,
                      overflow: TextOverflow.ellipsis,
                      maxLines: 1,
                      style: const TextStyle(
                        fontSize: 14,
                      ),
                    ),
                  ),
                ))
            .toList(),
        onChanged: onChanged,
        selectedItemBuilder: selectedItemBuilder,
        buttonStyleData: ButtonStyleData(
          height: buttonHeight ?? 40,
          width: buttonWidth ?? 140,
          padding: buttonPadding ?? const EdgeInsets.only(left: 14, right: 14),
          decoration: buttonDecoration ??
              BoxDecoration(
                borderRadius: BorderRadius.circular(14),
                border: Border.all(
                  color: Colors.black45,
                ),
              ),
          elevation: buttonElevation,
        ),
        iconStyleData: IconStyleData(
          icon: icon ?? const Icon(Icons.arrow_forward_ios_outlined),
          iconSize: iconSize ?? 12,
          iconEnabledColor: iconEnabledColor,
          iconDisabledColor: iconDisabledColor,
        ),
        dropdownStyleData: DropdownStyleData(
          //Max height for the dropdown menu & becoming scrollable if there are more items. If you pass Null it will take max height possible for the items.
          maxHeight: dropdownHeight ?? 200,
          width: dropdownWidth ?? 140,
          padding: dropdownPadding,
          decoration: dropdownDecoration ??
              BoxDecoration(
                borderRadius: BorderRadius.circular(14),
              ),
          elevation: dropdownElevation ?? 8,
          //Null or Offset(0, 0) will open just under the button. You can edit as you want.
          offset: offset,
          scrollbarTheme: ScrollbarThemeData(
            radius: scrollbarRadius ?? const Radius.circular(40),
            thickness: scrollbarThickness != null
                ? MaterialStateProperty.all<double>(scrollbarThickness!)
                : null,
            thumbVisibility: scrollbarAlwaysShow != null
                ? MaterialStateProperty.all<bool>(scrollbarAlwaysShow!)
                : null,
          ),
        ),
        menuItemStyleData: MenuItemStyleData(
          padding: itemPadding ?? const EdgeInsets.only(left: 14, right: 14),
        ),
      ),
    );
  }
}

Thanks

If something is missing or you want to add some feature, feel free to open a ticket or contribute!

LICENSE: MIT