dropdown_button2 2.3.9

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

Flutter DropdownButton2

Intro

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

• Features
• Options
• Installation
• Usage and Examples
  • 1. Simple DropdownButton2 with no styling
  • 2. DropdownButton2 with few styling and customization
  • 3. DropdownButton2 with items of different heights like dividers
  • 4. DropdownButton2 as Multiselect Dropdown with Checkboxes
  • 5. DropdownButton2 as Searchable Dropdown
  • 6. DropdownButton2 as Popup menu button using customButton parameter
  • 7. Using DropdownButtonFormField2 with Form
• CustomDropdownButton2 Widget "customize it to your needs"

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<DropdownMenuItem	Yes
selectedItemBuilder	A builder to customize how the selected item will be displayed on the button	DropdownButtonBuilder	No
value	The value of the currently selected [DropdownMenuItem]	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
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

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

Subclass MenuItemStyleData:

Option	Description	Type	Required
height	The height of the menu item	double	No
customHeights	Define different heights for the menu items (useful for adding dividers)	List	No
padding	The padding of menu items	EdgeInsetsGeometry	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
searchInnerWidget	The widget to be shown at the top of the dropdown menu for searchable dropdowns	Widget	No
searchInnerWidgetHeight	The height of the searchInnerWidget if used	double	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
dropdownButtonKey	The key of DropdownButton2 child widget	Key	No
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: ^2.3.8

import package

import 'package:dropdown_button2/dropdown_button2.dart';

Usage and Examples

1. Simple DropdownButton2 with no styling:

final List<String> items = [
  'Item1',
  'Item2',
  'Item3',
  'Item4',
];
String? selectedValue;

@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) => DropdownMenuItem<String>(
                    value: item,
                    child: Text(
                      item,
                      style: const TextStyle(
                        fontSize: 14,
                      ),
                    ),
                  ))
              .toList(),
          value: selectedValue,
          onChanged: (String? value) {
            setState(() {
              selectedValue = value;
            });
          },
          buttonStyleData: const ButtonStyleData(
            padding: EdgeInsets.symmetric(horizontal: 16),
            height: 40,
            width: 140,
          ),
          menuItemStyleData: const MenuItemStyleData(
            height: 40,
          ),
        ),
      ),
    ),
  );
}

2. DropdownButton2 with few styling and customization:

final List<String> items = [
  'Item1',
  'Item2',
  'Item3',
  'Item4',
  'Item5',
  'Item6',
  'Item7',
  'Item8',
];
String? selectedValue;

@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) => DropdownMenuItem<String>(
                    value: item,
                    child: Text(
                      item,
                      style: const TextStyle(
                        fontSize: 14,
                        fontWeight: FontWeight.bold,
                        color: Colors.white,
                      ),
                      overflow: TextOverflow.ellipsis,
                    ),
                  ))
              .toList(),
          value: selectedValue,
          onChanged: (value) {
            setState(() {
              selectedValue = 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(
            height: 40,
            padding: EdgeInsets.only(left: 14, right: 14),
          ),
        ),
      ),
    ),
  );
}

3. DropdownButton2 with items of different heights like dividers:

final List<String> items = [
  'Item1',
  'Item2',
  'Item3',
  'Item4',
];
String? selectedValue;

List<DropdownMenuItem<String>> _addDividersAfterItems(List<String> items) {
  final List<DropdownMenuItem<String>> menuItems = [];
  for (final String item in items) {
    menuItems.addAll(
      [
        DropdownMenuItem<String>(
          value: item,
          child: Padding(
            padding: const EdgeInsets.symmetric(horizontal: 8.0),
            child: Text(
              item,
              style: const TextStyle(
                fontSize: 14,
              ),
            ),
          ),
        ),
        //If it's last item, we will not add Divider after it.
        if (item != items.last)
          const DropdownMenuItem<String>(
            enabled: false,
            child: Divider(),
          ),
      ],
    );
  }
  return menuItems;
}

List<double> _getCustomItemsHeights() {
  final List<double> itemsHeights = [];
  for (int i = 0; i < (items.length * 2) - 1; i++) {
    if (i.isEven) {
      itemsHeights.add(40);
    }
    //Dividers indexes will be the odd indexes
    if (i.isOdd) {
      itemsHeights.add(4);
    }
  }
  return itemsHeights;
}

@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: _addDividersAfterItems(items),
          value: selectedValue,
          onChanged: (String? value) {
            setState(() {
              selectedValue = value;
            });
          },
          buttonStyleData: const ButtonStyleData(
            padding: EdgeInsets.symmetric(horizontal: 16),
            height: 40,
            width: 140,
          ),
          dropdownStyleData: const DropdownStyleData(
            maxHeight: 200,
          ),
          menuItemStyleData: MenuItemStyleData(
            padding: const EdgeInsets.symmetric(horizontal: 8.0),
            customHeights: _getCustomItemsHeights(),
          ),
          iconStyleData: const IconStyleData(
            openMenuIcon: Icon(Icons.arrow_drop_up),
          ),
        ),
      ),
    ),
  );
}

4. DropdownButton2 as Multiselect Dropdown with Checkboxes:

final List<String> items = [
  'Item1',
  'Item2',
  'Item3',
  'Item4',
];
List<String> selectedItems = [];

@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 DropdownMenuItem(
              value: item,
              //disable default onTap to avoid closing menu when selecting an item
              enabled: false,
              child: StatefulBuilder(
                builder: (context, menuSetState) {
                  final isSelected = selectedItems.contains(item);
                  return InkWell(
                    onTap: () {
                      isSelected ? selectedItems.remove(item) : selectedItems.add(item);
                      //This rebuilds the StatefulWidget to update the button's text
                      setState(() {});
                      //This rebuilds the dropdownMenu Widget to update the check mark
                      menuSetState(() {});
                    },
                    child: 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(),
          //Use last selected item as the current value so if we've limited menu height, it scroll to last item.
          value: selectedItems.isEmpty ? null : selectedItems.last,
          onChanged: (value) {},
          selectedItemBuilder: (context) {
            return items.map(
              (item) {
                return Container(
                  alignment: AlignmentDirectional.center,
                  child: Text(
                    selectedItems.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(
            height: 40,
            padding: EdgeInsets.zero,
          ),
        ),
      ),
    ),
  );
}

5. DropdownButton2 as Searchable Dropdown:

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

String? selectedValue;
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) => DropdownMenuItem(
                    value: item,
                    child: Text(
                      item,
                      style: const TextStyle(
                        fontSize: 14,
                      ),
                    ),
                  ))
              .toList(),
          value: selectedValue,
          onChanged: (value) {
            setState(() {
              selectedValue = value;
            });
          },
          buttonStyleData: const ButtonStyleData(
            padding: EdgeInsets.symmetric(horizontal: 16),
            height: 40,
            width: 200,
          ),
          dropdownStyleData: const DropdownStyleData(
            maxHeight: 200,
          ),
          menuItemStyleData: const MenuItemStyleData(
            height: 40,
          ),
          dropdownSearchData: DropdownSearchData(
            searchController: textEditingController,
            searchInnerWidgetHeight: 50,
            searchInnerWidget: 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),
                  ),
                ),
              ),
            ),
            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:

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

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

class _MyHomePageState extends State<MyHomePage> {
  @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) => DropdownMenuItem<MenuItem>(
                  value: item,
                  child: MenuItems.buildItem(item),
                ),
              ),
              const DropdownMenuItem<Divider>(enabled: false, child: Divider()),
              ...MenuItems.secondItems.map(
                (item) => DropdownMenuItem<MenuItem>(
                  value: item,
                  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: MenuItemStyleData(
              customHeights: [
                ...List<double>.filled(MenuItems.firstItems.length, 48),
                8,
                ...List<double>.filled(MenuItems.secondItems.length, 48),
              ],
              padding: const 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:

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

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

class _MyHomePageState extends State<MyHomePage> {
  @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/city.jpg',
                  ),
                  fit: BoxFit.cover,
                ),
              ),
            ),
            openWithLongPress: true,
            items: [
              ...MenuItems.firstItems.map(
                (item) => DropdownMenuItem<MenuItem>(
                  value: item,
                  child: MenuItems.buildItem(item),
                ),
              ),
              const DropdownMenuItem<Divider>(enabled: false, child: Divider()),
              ...MenuItems.secondItems.map(
                (item) => DropdownMenuItem<MenuItem>(
                  value: item,
                  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: MenuItemStyleData(
              customHeights: [
                ...List<double>.filled(MenuItems.firstItems.length, 48),
                8,
                ...List<double>.filled(MenuItems.secondItems.length, 48),
              ],
              padding: const 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:

final List<String> genderItems = [
  'Male',
  'Female',
];

String? selectedValue;

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) => DropdownMenuItem<String>(
                        value: item,
                        child: Text(
                          item,
                          style: const TextStyle(
                            fontSize: 14,
                          ),
                        ),
                      ))
                  .toList(),
              validator: (value) {
                if (value == null) {
                  return 'Please select gender.';
                }
                return null;
              },
              onChanged: (value) {
                //Do something when selected item is changed.
              },
              onSaved: (value) {
                selectedValue = value.toString();
              },
              buttonStyleData: const ButtonStyleData(
                padding: EdgeInsets.only(right: 8),
              ),
              iconStyleData: const IconStyleData(
                icon: Icon(
                  Icons.arrow_drop_down,
                  color: Colors.black45,
                ),
                iconSize: 24,
              ),
              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()) {
                  _formKey.currentState!.save();
                }
              },
              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.value,
    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 String? value;
  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,
            ),
          ),
        ),
        value: value,
        items: dropdownItems
            .map((String item) => DropdownMenuItem<String>(
                  value: item,
                  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(
          height: itemHeight ?? 40,
          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