Flutter DropdownButton - Add title for separating items

Question

Im trying to implement a DropdownButton that can separate specific items from each other with a title (see desired output on image below, the titles are in green)

Like in the example I would like to add these green titles to my existing DropdownButton, but did not find anything that showed me how to add something else than items to a DropdownButton

I also tried to switch from DropdownButton to a ListView with ExpansionTile but I would like to keep the behaviour of the DropdownButton...

Is it possible to add these titles to the DropdownButton items? Or shourd I try to achive it by a other way? Im stuck at the moment and dont know how to proceed

Solution 1

try this code in dartpad:

 import 'package:flutter/material.dart';

void main() {
  runApp(
    MaterialApp(
      debugShowCheckedModeBanner: false,
      
      home: MyApp(),
    ),
  );
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return HomeScreen();
  }
}

class HomeScreen extends StatefulWidget {
  @override
  HomeScreenState createState() => HomeScreenState();
}

class HomeScreenState extends State<HomeScreen> {
  String dropdownValue;
  List<Product> products = [
    Product(name: 'sep1', type: 'sep'),
    Product(name: 'milk', type: 'data'),
    Product(name: 'oil', type: 'data'),
    Product(name: 'sep2', type: 'sep'),
    Product(name: 'suger', type: 'data'),
    Product(name: 'salt', type: 'data'),
    Product(name: 'sep3', type: 'sep'),
    Product(name: 'potatoe', type: 'data'),
    Product(name: 'tomatoe', type: 'data'),
    Product(name: 'apple', type: 'data'),
  ];

  @override
  void initState() {
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('text')),
      body: Column(
        children: [
          Text('test'),
          Expanded(
            child: DropdownButton<String>(
              value: dropdownValue,
              items: products.map((value) {
                return DropdownMenuItem(
                  value: value.name,
                  child: value.type == 'data'
                      ? Text(value.name)
                      : Divider(
                          color: Colors.red,
                          thickness: 3,
                        ),
                );
              }).toList(),
              onChanged: (newValue) {
                
                setState(() {
                  
                    dropdownValue = newValue;
                  
                });
                print('$newValue $dropdownValue');
                
              },
            ),
          ),
        ],
      ),
    );
  }
}

class Product {
  String name;
  String type;

  Product({this.name, this.type});
}

Solution 2

In addition to Ali Tenni's answer you can also subclass DropdownMenuItem like this:

class DropdownMenuItemSeparator<T> extends DropdownMenuItem<T> {
  DropdownMenuItemSeparator() : super(
    enabled: false,     // As of Flutter 2.5.
    child: Container(), // Trick the assertion.
  ); 

  @override
  Widget build(BuildContext context) {
    return Divider(thickness: 3);
  }
}

This will make the separator more narrow because otherwise the default build() adds some min height.

UPD 2021-09-14 Below is no longer relevant as the feature is implemented in Flutter 2.5. The code above updated accordingly.

This solves one of the two problems. Unfortunately, the second and the larger problem is that the separator is still tappable, and the tap closes the dropdown. To address this, I submitted a feature request to Flutter: https://github.com/flutter/flutter/issues/75487