Is there an equivalent widget in flutter to the "select multiple" element in HTML - select

Question

I am searching for a widget in flutter that is equal to
<select multiple=""></select>
in flutter.
An example implementation (for the web) is MaterializeCSS Select Multiple
As seen above I should be able to provide a list of items (with some of them preselected) and at the end retrieve a list of selected items or a map or something else.
An example implementation or a link to a documentation is very appreciated.

Answer 1

I don't think that a widget like that currently exists in Flutter, but you can build one yourself.
On mobile phones with limited screen space it would probably make sense to display a dialog with a submit button, like this native Android dialog.
Here is a rough sketch how to implement such a dialog in less than 100 lines of code:
class MultiSelectDialogItem<V> {
const MultiSelectDialogItem(this.value, this.label);
final V value;
final String label;
}
class MultiSelectDialog<V> extends StatefulWidget {
MultiSelectDialog({Key key, this.items, this.initialSelectedValues}) : super(key: key);
final List<MultiSelectDialogItem<V>> items;
final Set<V> initialSelectedValues;
#override
State<StatefulWidget> createState() => _MultiSelectDialogState<V>();
}
class _MultiSelectDialogState<V> extends State<MultiSelectDialog<V>> {
final _selectedValues = Set<V>();
void initState() {
super.initState();
if (widget.initialSelectedValues != null) {
_selectedValues.addAll(widget.initialSelectedValues);
}
}
void _onItemCheckedChange(V itemValue, bool checked) {
setState(() {
if (checked) {
_selectedValues.add(itemValue);
} else {
_selectedValues.remove(itemValue);
}
});
}
void _onCancelTap() {
Navigator.pop(context);
}
void _onSubmitTap() {
Navigator.pop(context, _selectedValues);
}
#override
Widget build(BuildContext context) {
return AlertDialog(
title: Text('Select animals'),
contentPadding: EdgeInsets.only(top: 12.0),
content: SingleChildScrollView(
child: ListTileTheme(
contentPadding: EdgeInsets.fromLTRB(14.0, 0.0, 24.0, 0.0),
child: ListBody(
children: widget.items.map(_buildItem).toList(),
),
),
),
actions: <Widget>[
FlatButton(
child: Text('CANCEL'),
onPressed: _onCancelTap,
),
FlatButton(
child: Text('OK'),
onPressed: _onSubmitTap,
)
],
);
}
Widget _buildItem(MultiSelectDialogItem<V> item) {
final checked = _selectedValues.contains(item.value);
return CheckboxListTile(
value: checked,
title: Text(item.label),
controlAffinity: ListTileControlAffinity.leading,
onChanged: (checked) => _onItemCheckedChange(item.value, checked),
);
}
}
You can use it like this:
void _showMultiSelect(BuildContext context) async {
final items = <MultiSelectDialogItem<int>>[
MultiSelectDialogItem(1, 'Dog'),
MultiSelectDialogItem(2, 'Cat'),
MultiSelectDialogItem(3, 'Mouse'),
];
final selectedValues = await showDialog<Set<int>>(
context: context,
builder: (BuildContext context) {
return MultiSelectDialog(
items: items,
initialSelectedValues: [1, 3].toSet(),
);
},
);
print(selectedValues);
}

Answer 2

Is this what you want?
In case you need a short and ready to use code, follow this article
import 'package:flutter/material.dart';
import 'package:multiple_selection_dialogue_app/widgets/multi_select_dialog.dart';
/// A demo page that displays an [ElevatedButton]
class DemoPage extends StatelessWidget {
#override
Widget build(BuildContext context) {
/// Stores the selected flavours
List<String> flavours = [];
return ElevatedButton(
child: Text('Flavours'),
onPressed: () async {
flavours = await showDialog<List<String>>(
context: context,
builder: (_) => MultiSelectDialog(
question: Text('Select Your Flavours'),
answers: [
'Chocolate',
'Caramel',
'Vanilla',
'Peanut Butter'
])) ??
[];
print(flavours);
// Logic to save selected flavours in the database
});
}
}
import 'package:flutter/material.dart';
/// A Custom Dialog that displays a single question & list of answers.
class MultiSelectDialog extends StatelessWidget {
/// List to display the answer.
final List<String> answers;
/// Widget to display the question.
final Widget question;
/// List to hold the selected answer
/// i.e. ['a'] or ['a','b'] or ['a','b','c'] etc.
final List<String> selectedItems = [];
/// Map that holds selected option with a boolean value
/// i.e. { 'a' : false}.
static Map<String, bool> mappedItem;
MultiSelectDialog({this.answers, this.question});
/// Function that converts the list answer to a map.
Map<String, bool> initMap() {
return mappedItem = Map.fromIterable(answers,
key: (k) => k.toString(),
value: (v) {
if (v != true && v != false)
return false;
else
return v as bool;
});
}
#override
Widget build(BuildContext context) {
if (mappedItem == null) {
initMap();
}
return SimpleDialog(
title: question,
children: [
...mappedItem.keys.map((String key) {
return StatefulBuilder(
builder: (_, StateSetter setState) => CheckboxListTile(
title: Text(key), // Displays the option
value: mappedItem[key], // Displays checked or unchecked value
controlAffinity: ListTileControlAffinity.platform,
onChanged: (value) => setState(() => mappedItem[key] = value)),
);
}).toList(),
Align(
alignment: Alignment.center,
child: ElevatedButton(
style: ButtonStyle(visualDensity: VisualDensity.comfortable),
child: Text('Submit'),
onPressed: () {
// Clear the list
selectedItems.clear();
// Traverse each map entry
mappedItem.forEach((key, value) {
if (value == true) {
selectedItems.add(key);
}
});
// Close the Dialog & return selectedItems
Navigator.pop(context, selectedItems);
}))
],
);
}
}
import 'package:flutter/material.dart';
import 'package:multiple_selection_dialogue_app/pages/demo_page.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
debugShowCheckedModeBanner: false,
home: Scaffold(
body: Center(
child: DemoPage(),
),
),
);
}
}