Flutter: DropdownButton Example

This article walks you through an end-to-end complete example of implementing the DropdownButton widget in Flutter.

Overview

A Quick Note

When a DropdownButton widget gets pressed, a menu with items will show up and let the user select one item from them. The selected item will be displayed on the button when the menu disappears.

The items of the DropdownButton are implemented by using a list of DropdownMenuItem widgets:

DropdownButton<T>(
  value: T?,
  items: List<DropdownMenuItem<T>>?,
)

The type of the value and the type specialized for each DropdownMenuItem must be the same.

Setting the Width for a Dropdown Button

You can set the width for a DropdownButton by setting its isExpanded parameter to true and wrapping it inside a fixed-size Container or SIzedBox.

Hiding the underline

Below are two different ways to remove the underline of a DropdownButton.

1. Set the underline parameter to an empty Container:

underline: Container()

2. Place the DropdownButton widget inside a DropdownButtonHideUnderline widget:

DropdownButtonHideUnderline(
            child: DropdownButton(/* ... */),
)

Words might be boring and confusing. The example below will help you get a better understanding.

The Example

Preview

The demo app we are going to make contains a rounded dropdown button with white hint text. Its width is 300px and its underline is invisible.

The dropdown menu is amber and its text is dark. The selected item will have a custom text style, thanks to selectedItemBuilder.

The Complete Code

The full source code in main.dart with explanations:

// main.dart
import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
        // Remove the debug banner
        debugShowCheckedModeBanner: false,
        title: 'Kindacode.com',
        theme: ThemeData(
          primarySwatch: Colors.indigo,
        ),
        home: const HomePage());
  }
}

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  State<HomePage> createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  // define a list of options for the dropdown
  final List<String> _animals = ["Dog", "Cat", "Crocodile", "Dragon"];

  // the selected value
  String? _selectedAnimal;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Kindacode.com'),
      ),
      body: Center(
        child: Container(
          padding: const EdgeInsets.symmetric(vertical: 5, horizontal: 15),
          width: 300,
          decoration: BoxDecoration(
              color: Theme.of(context).primaryColor,
              borderRadius: BorderRadius.circular(30)),
          child: DropdownButton<String>(
            value: _selectedAnimal,
            onChanged: (value) {
              setState(() {
                _selectedAnimal = value;
              });
              debugPrint("You selected $_selectedAnimal");
            },
            hint: const Center(
                child: Text(
              'Select the aniaml you love',
              style: TextStyle(color: Colors.white),
            )),
            // Hide the default underline
            underline: Container(),
            // set the color of the dropdown menu
            dropdownColor: Colors.amber,
            icon: const Icon(
              Icons.arrow_downward,
              color: Colors.yellow,
            ),
            isExpanded: true,

            // The list of options
            items: _animals
                .map((e) => DropdownMenuItem(
                      value: e,
                      child: Container(
                        alignment: Alignment.centerLeft,
                        child: Text(
                          e,
                          style: const TextStyle(fontSize: 18),
                        ),
                      ),
                    ))
                .toList(),

            // Customize the selected item
            selectedItemBuilder: (BuildContext context) => _animals
                .map((e) => Center(
                      child: Text(
                        e,
                        style: const TextStyle(
                            fontSize: 18,
                            color: Colors.amber,
                            fontStyle: FontStyle.italic,
                            fontWeight: FontWeight.bold),
                      ),
                    ))
                .toList(),
          ),
        ),
      ),
    );
  }
}

Conclusion

We’ve explored the fundamentals of the DropdownButton and DropdownMenuItem widget in Flutter. If you’d like to learn more new and interesting things in Flutter and Dart, take a look at the following articles:

• 2 Ways to Create Flipping Card Animation in Flutter
• Flutter: Making a Dropdown Multiselect with Checkboxes
• Flutter: How to Make Spinning Animation without Plugins
• Using Cascade Notation in Dart and Flutter
• Sorting Lists in Dart and Flutter (5 Examples)
• Flutter: Add a Search Field to an App Bar (2 Approaches)

You can also take a tour around our Flutter topic page and Dart topic page to see the latest tutorials and examples.