How to Set/Update State of StatefulWidget from other StatefulWidget in Flutter?
Screenshot (Parent to child, Child to parent):
This examples shows calling a method
- Defined in Child widget from Parent widget.
- Defined in Parent widget from Child widget.
Code:
class ParentPage extends StatelessWidget {
final GlobalKey<ChildPageState> _key = GlobalKey();
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(title: Text("Parent")),
body: Center(
child: Column(
children: <Widget>[
Expanded(
child: Container(
color: Colors.grey,
width: double.infinity,
alignment: Alignment.center,
child: ElevatedButton(
child: Text("Call method in child"),
onPressed: () => _key.currentState!.methodInChild(), // calls method in child
),
),
),
Text("Above = Parent\nBelow = Child"),
Expanded(
child: ChildPage(
key: _key,
function: methodInParent,
),
),
],
),
),
);
}
methodInParent() => Fluttertoast.showToast(msg: "Method called in parent", gravity: ToastGravity.CENTER);
}
class ChildPage extends StatefulWidget {
final VoidCallback function;
ChildPage({Key? key, required this.function}) : super(key: key);
@override
ChildPageState createState() => ChildPageState();
}
class ChildPageState extends State<ChildPage> {
@override
Widget build(BuildContext context) {
return Container(
color: Colors.teal,
width: double.infinity,
alignment: Alignment.center,
child: ElevatedButton(
child: Text("Call method in parent"),
onPressed: () => widget.function(), // calls method in parent
),
);
}
methodInChild() => Fluttertoast.showToast(msg: "Method called in child");
}
1.On Child Widget : add parameter Function paramter
class ChildWidget extends StatefulWidget {
final Function() notifyParent;
ChildWidget({Key key, @required this.notifyParent}) : super(key: key);
}
2.On Parent Widget : create a Function for the child to callback
refresh() {
setState(() {});
}
3.On Parent Widget : pass parentFunction to Child Widget
new ChildWidget( notifyParent: refresh );
4.On Child Widget : call the Parent Function
widget.notifyParent();
Old Solutions:
- Create a global instance of _MyHomePageState. Use this instance in _SubState as _myHomePageState.setState
- No need to create a global instance. Instead, just pass the parent instance to the child widget
New Solution: Passing a callback seems the better solution than above solutions
CODE UPDATED AS PER FLUTTER 2.0:
import 'package:flutter/material.dart';
void main() => runApp(new MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'Flutter Demo',
theme: new ThemeData(
primarySwatch: Colors.blue,
),
home: new MyHomePage(),
);
}
}
EdgeInsets globalMargin =
const EdgeInsets.symmetric(horizontal: 20.0, vertical: 20.0);
TextStyle textStyle = const TextStyle(
fontSize: 100.0,
color: Colors.black,
);
class MyHomePage extends StatefulWidget {
@override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int number = 0;
@override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text('SO Help'),
),
body: new Column(
children: <Widget>[
new Text(
number.toString(),
style: textStyle,
),
new GridView.count(
crossAxisCount: 2,
shrinkWrap: true,
scrollDirection: Axis.vertical,
children: <Widget>[
new InkResponse(
child: new Container(
margin: globalMargin,
color: Colors.green,
child: new Center(
child: new Text(
"+",
style: textStyle,
),
)),
onTap: () {
setState(() {
this.number++;
});
},
),
new Sub(onTap: () {
setState(() {
this.number--;
});
}),
],
),
],
),
floatingActionButton: new FloatingActionButton(
onPressed: () {
setState(() {});
},
child: new Icon(Icons.update),
),
);
}
}
class Sub extends StatelessWidget {
final Function onTap;
Sub({this.onTap});
@override
Widget build(BuildContext context) {
return new InkResponse(
child: new Container(
margin: globalMargin,
color: Colors.red,
child: new Center(
child: new Text(
"-",
style: textStyle,
),
),
),
onTap: this.onTap,
);
}
}
Just let me know if it works.