how to use setState inside another class? - flutter

Question

I am having issues with setting state of variable because i am using other class outside stateful widget. On line 115 inside buildActions method i want to set _selectedStores = selectedStores;. How can i set the state?
I tried using callback but got no luck.
import 'package:flutter/material.dart';
class SearchDemo extends StatefulWidget {
#override
_SearchDemoState createState() => _SearchDemoState();
}
class _SearchDemoState extends State<SearchDemo> {
final _SearchDemoSearchDelegate _delegate = _SearchDemoSearchDelegate();
final GlobalKey<ScaffoldState> _scaffoldKey = GlobalKey<ScaffoldState>();
String _lastSearchSelected;
#override
Widget build(BuildContext context) {
return Scaffold(
key: _scaffoldKey,
appBar: AppBar(
title: const Text('Search Demo'),
actions: <Widget>[
IconButton(
tooltip: 'Search',
icon: const Icon(Icons.search),
onPressed: () async {
final String selected = await showSearch<String>(
context: context,
delegate: _delegate,
);
if (selected != null && selected != _lastSearchSelected) {
setState(() {
_lastSearchSelected = selected;
});
}
},
),
],
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text('Last search: ${_lastSearchSelected ?? 'NONE'}.'),
],
),
),
);
}
}
class Stores {
int id;
String name;
Stores(this.id, this.name);
static List<Stores> getStores() {
return <Stores>[
Stores(1, 'Amazon'),
Stores(2, 'Flipkart'),
Stores(3, 'Snapdeal'),
];
}
}
class _SearchDemoSearchDelegate extends SearchDelegate<String> {
List<Stores> _stores = Stores.getStores();
List<DropdownMenuItem<Stores>> _dropdownMenuItems;
Stores _selectedStores;
List<DropdownMenuItem<Stores>> buildDropdownMenuItems(List stores) {
List<DropdownMenuItem<Stores>> items = List();
for (Stores stores in stores) {
items.add(
DropdownMenuItem(
value: stores,
child: Text(stores.name),
),
);
}
return items;
}
#override
Widget buildLeading(BuildContext context) {
return IconButton(
tooltip: 'Back',
icon: AnimatedIcon(
icon: AnimatedIcons.menu_arrow,
progress: transitionAnimation,
),
onPressed: () {
close(context, null);
},
);
}
#override
Widget buildSuggestions(BuildContext context) {
return _SuggestionList(
query: query,
onSelected: (String suggestion) {
print(suggestion);
},
);
}
#override
Widget buildResults(BuildContext context) {}
#override
List<Widget> buildActions(BuildContext context) {
_dropdownMenuItems = buildDropdownMenuItems(_stores);
_selectedStores = _dropdownMenuItems[0].value;
void onChangeDropdownItem(Stores selectedStores) {
setState(() {
_selectedStores = selectedStores;
});
}
return <Widget>[
query.isEmpty
? Container(
padding: const EdgeInsets.only(right: 5.0, top: 5.0),
child: DropdownButtonHideUnderline(
child: DropdownButton(
elevation: 0,
value: _selectedStores,
items: _dropdownMenuItems,
onChanged: onChangeDropdownItem,
),
),
)
: IconButton(
tooltip: 'Clear',
icon: const Icon(Icons.clear),
onPressed: () {
query = '';
},
),
];
}
}
List<String> getHistory() {
//Get Last Searched products from device storage *Pending*
final List<String> _history = <String>[
"iPhone X 64GB Silver",
"Galaxy S10+ White",
"Apple Watch Series 3",
"Samson C01UPRO",
"Cooler Master masterbox 5"
];
return _history;
}
class _SuggestionList extends StatelessWidget {
const _SuggestionList({this.query, this.onSelected});
final String query;
final ValueChanged<String> onSelected;
#override
Widget build(BuildContext context) {
//Get Data From API *Pending*
final List<String> _data = <String>[
"iPhone X 64GB Silver",
"Galaxy S10+ White",
"Apple Watch Series 3",
"Samson C01UPRO",
"Cooler Master Masterbox 5"
];
final List<String> suggestions = query.isEmpty
? getHistory()
: _data
.where((p) => p.toLowerCase().contains(query.toLowerCase()))
.toList();
return ListView.builder(
itemCount: suggestions.length,
itemBuilder: (BuildContext context, int i) {
final String suggestion = suggestions[i];
return ListTile(
leading: query.isEmpty ? const Icon(Icons.history) : const Icon(null),
title: Text(suggestion),
onTap: () {
onSelected(suggestion);
},
);
},
);
}
}

Answer 1

The method setState is only part of StatefulWidgets and that information shouldn't be passed around. It's not recommended and is not a good development practice. Can you do it? Yes, like this:
class OtherClass {
final State state;
OtherClass(this.state);
}
class Home extends StatefulWidget {
#override
_HomeState createState() => _HomeState();
}
class _HomeState extends State<Home> {
#override
void initState() {
super.initState();
OtherClass(this);
}
}
But, again, I do not recommend this at all. You should be using some kind of Future or Stream to send your data to your StatefulWidget and then use your setState there, where it should be.