Related
class SnackBarPage extends StatelessWidget {
const SnackBarPage({super.key});
#override
Widget build(BuildContext context) {
return Center(
child: ElevatedButton(
onPressed: () {
final snackBar = SnackBar(
content: const Text('Yay! A SnackBar!'),
action: SnackBarAction(
label: 'Undo',
onPressed: () {
// Some code to undo the change.
},
),
);
// Find the ScaffoldMessenger in the widget tree
// and use it to show a SnackBar.
ScaffoldMessenger.of(context).showSnackBar(snackBar);
},
child: const Text('Show SnackBar'),
),
);
}
}
Above is the code that I want to translate into ClojureDart.
However, ClojureDart is a dialect of Clojure which is a functional language,
Found!
I had to use cljd.flutter.alpha library that exports f/widget, and wraps it around the scaffold.
Then, within the widget, I had to use the inherit keyword with the widget I wanted to inherit, in my case, ScaffoldMessenger. After doing so, I have access to the ScaffoldMessenger object with a variable with a kebab-case name. While it can be confusing without seeing it, it gives something like that :
(f/widget
:inherit [m/ScaffoldMessenger]
(m/Scaffold
...
:onPressed (.showSnackBar scaffold-messenger snackbar)
...))
With scaffold-messenger variable corresponding to m/ScaffoldMessenger, and snackbar being a function that returns a m/SnackBar widget.
As I'm learning Flutter I've come to navigation. I want to pass data between screens similarly to passing data between Activities in Android and passing data between View Controllers in iOS. How do I do it in Flutter?
Related questions:
The best way to passing data between widgets in Flutter
Flutter pass data between widgets?
Flutter/ How to pass and get data between Statefulwidget
This answer will cover both passing data forward and passing data back. Unlike Android Activities and iOS ViewControllers, different screens in Flutter are just widgets. Navigating between them involves creating something called a route and using the Navigator to push and pop the routes on and off the stack.
Passing data forward to the next screen
To send data to the next screen you do the following things:
Make the SecondScreen constructor take a parameter for the type of data that you want to send to it. In this particular example, the data is defined to be a String value and is set here with this.text.
class SecondScreen extends StatelessWidget {
final String text;
SecondScreen({Key key, #required this.text}) : super(key: key);
...
Then use the Navigator in the FirstScreen widget to push a route to the SecondScreen widget. You put the data that you want to send as a parameter in its constructor.
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => SecondScreen(text: 'Hello',),
));
The full code for main.dart is here:
import 'package:flutter/material.dart';
void main() {
runApp(MaterialApp(
title: 'Flutter',
home: FirstScreen(),
));
}
class FirstScreen extends StatefulWidget {
#override
_FirstScreenState createState() {
return _FirstScreenState();
}
}
class _FirstScreenState extends State<FirstScreen> {
// this allows us to access the TextField text
TextEditingController textFieldController = TextEditingController();
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(title: Text('First screen')),
body: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Padding(
padding: const EdgeInsets.all(32.0),
child: TextField(
controller: textFieldController,
style: TextStyle(
fontSize: 24,
color: Colors.black,
),
),
),
RaisedButton(
child: Text(
'Go to second screen',
style: TextStyle(fontSize: 24),
),
onPressed: () {
_sendDataToSecondScreen(context);
},
)
],
),
);
}
// get the text in the TextField and start the Second Screen
void _sendDataToSecondScreen(BuildContext context) {
String textToSend = textFieldController.text;
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => SecondScreen(text: textToSend,),
));
}
}
class SecondScreen extends StatelessWidget {
final String text;
// receive data from the FirstScreen as a parameter
SecondScreen({Key key, #required this.text}) : super(key: key);
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(title: Text('Second screen')),
body: Center(
child: Text(
text,
style: TextStyle(fontSize: 24),
),
),
);
}
}
Passing data back to the previous screen
When passing data back you need to do the following things:
In the FirstScreen, use the Navigator to push (start) the SecondScreen in an async method and wait for the result that it will return when it finishes.
final result = await Navigator.push(
context,
MaterialPageRoute(
builder: (context) => SecondScreen(),
));
In the SecondScreen, include the data that you want to pass back as a parameter when you pop the Navigator.
Navigator.pop(context, 'Hello');
Then in the FirstScreen the await will finish and you can use the result.
setState(() {
text = result;
});
Here is the complete code for main.dart for your reference.
import 'package:flutter/material.dart';
void main() {
runApp(MaterialApp(
title: 'Flutter',
home: FirstScreen(),
));
}
class FirstScreen extends StatefulWidget {
#override
_FirstScreenState createState() {
return _FirstScreenState();
}
}
class _FirstScreenState extends State<FirstScreen> {
String text = 'Text';
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(title: Text('First screen')),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Padding(
padding: const EdgeInsets.all(32.0),
child: Text(
text,
style: TextStyle(fontSize: 24),
),
),
RaisedButton(
child: Text(
'Go to second screen',
style: TextStyle(fontSize: 24),
),
onPressed: () {
_awaitReturnValueFromSecondScreen(context);
},
)
],
),
),
);
}
void _awaitReturnValueFromSecondScreen(BuildContext context) async {
// start the SecondScreen and wait for it to finish with a result
final result = await Navigator.push(
context,
MaterialPageRoute(
builder: (context) => SecondScreen(),
));
// after the SecondScreen result comes back update the Text widget with it
setState(() {
text = result;
});
}
}
class SecondScreen extends StatefulWidget {
#override
_SecondScreenState createState() {
return _SecondScreenState();
}
}
class _SecondScreenState extends State<SecondScreen> {
// this allows us to access the TextField text
TextEditingController textFieldController = TextEditingController();
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(title: Text('Second screen')),
body: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Padding(
padding: const EdgeInsets.all(32.0),
child: TextField(
controller: textFieldController,
style: TextStyle(
fontSize: 24,
color: Colors.black,
),
),
),
RaisedButton(
child: Text(
'Send text back',
style: TextStyle(fontSize: 24),
),
onPressed: () {
_sendDataBack(context);
},
)
],
),
);
}
// get the text in the TextField and send it back to the FirstScreen
void _sendDataBack(BuildContext context) {
String textToSendBack = textFieldController.text;
Navigator.pop(context, textToSendBack);
}
}
This solution is very easy by passing variables in constructor:
first page:
Navigator.of(context).push(MaterialPageRoute(builder:(context)=>SecondPage('something')));
second page:
class SecondPage extends StatefulWidget {
String something;
SecondPage(this.something);
#override
State<StatefulWidget> createState() {
return SecondPageState(this.something);
}
}
class SecondPageState extends State<SecondPage> {
String something;
SecondPageState(this.something);
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
//now you have passing variable
title: Text(something),
),
...
}
Get Perfect Solution :
From 1st Screen navigate to others as:
Navigator.pushNamed(context, "second",arguments: {"name" :
"Bijendra", "rollNo": 65210});
},
On Second Screen in build method get as :
#override
Widget build(BuildContext context) {
final Map<String, Object>rcvdData = ModalRoute.of(context).settings.arguments;
print("rcvd fdata ${rcvdData['name']}");
print("rcvd fdata ${rcvdData}");
return Scaffold(appBar: AppBar(title: Text("Second")),
body: Container(child: Column(children: <Widget>[
Text("Second"),
],),),);
}
Easiest way
FirstPage.dart
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => PasswordRoute(usernameController)));
//usernameController is String value,If you want to pass multiple values add all
SecondPage.dart
class PasswordRoute extends StatefulWidget {
final String usernameController;//if you have multiple values add here
PasswordRoute(this.usernameController, {Key key}): super(key: key);//add also..example this.abc,this...
#override
State<StatefulWidget> createState() => _PasswordPageState();
}
class _PasswordPageState extends State<PasswordRoute> {
#override
Widget build(BuildContext context) {
...child: Text(widget.usernameController);
}
}
Answers above are useful for a small app, but if you want to remove the headache of continuously worrying about a widgets state, Google presented the Provider package.
https://pub.dev/packages/provider
Have a look into that one, or watch these videos from Andrea Bizzotto:
https://www.youtube.com/watch?v=MkFjtCov62g // Provider: The Essential Guide
https://www.youtube.com/watch?v=O71rYKcxUgA&t=258s // Provider: Introduction
Learn how to use the Provider package, and you are set for life :)
First Screen :
//send data to second screen
Navigator.push(context, MaterialPageRoute(builder: (context) {
return WelcomeUser(usernameController.text);
}));
Second Screen :
//fetch data from first screen
final String username;
WelcomeUser(this.username);
//use data to display
body: Container(
child: Center(
child: Text("Welcome "+widget.username,
textAlign: TextAlign.center,
),
),
),
Navigators in Flutter are similar to the Intent in Android.
There are two classes we are dealing with FirstScreen and SecondScreen.
In order to pass the data between the first screen to second do the following:
First of all add parameter in the SecondScreen class constructor
Now in the FirstScreen class provide the parameter
Navigator.push(context, MaterialPageRoute(builder: (context)=>SecondScreen(key_name:"Desired Data"));
So in the above line the "key_name" is the name of the parameter given in the SecondScreen class.
The "Desired Data" is data should be passed through the key to the SecondScreen class.
That's it you are done!!!
Passing Data to back screen flutter
Home Page
import 'package:flutter/material.dart';
import 'package:flutter/src/widgets/container.dart';
import 'package:flutter/src/widgets/framework.dart';
import 'package:sqflite_offline/View/Add_data.dart';
class HomeScreen extends StatefulWidget {
const HomeScreen({super.key});
#override
State<HomeScreen> createState() => _HomeScreenState();
}
class _HomeScreenState extends State<HomeScreen> {
List<Method> items = []; // => List of items that come form next page.
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("Hello"),
),
floatingActionButton: FloatingActionButton(
onPressed: () {
Navigator.of(context)
.push<Method>(MaterialPageRoute(builder: (_) => AddData()))
// fetching data form next page.
.then((value) => setState(() {
if (value?.title_Ctr != "" && value?.desc_Ctr != "") {
items.add(Method(
title_Ctr: value!.title_Ctr,
desc_Ctr: value.desc_Ctr));
}
}));
},
child: Icon(Icons.add),
),
body: items.isNotEmpty
? Column(children: [
Expanded(
child: ListView.builder(
itemCount: items.length,
itemBuilder: ((context, index) {
return Container(
margin:
EdgeInsets.only(top: 10, left: 10, right: 10),
padding: EdgeInsets.only(left: 10, right: 10),
height: 80,
decoration: BoxDecoration(
color: Colors.pinkAccent,
borderRadius: BorderRadius.circular(10)),
child: Center(
child: ListTile(
title: Text(items[index].title_Ctr),
subtitle: Text(items[index].desc_Ctr),
leading: Icon(Icons.emoji_people),
),
),
);
})))
])
: Center(
child: Text("No Record Found"),
));
}
}
Add List Page
import 'package:flutter/material.dart';
import 'package:flutter/src/widgets/container.dart';
import 'package:flutter/src/widgets/framework.dart';
class AddData extends StatefulWidget {
const AddData({super.key});
#override
State<AddData> createState() => _AddDataState();
}
// Creating a Class and constructor.
class Method {
late String title_Ctr;
late String desc_Ctr;
Method({required this.title_Ctr, required this.desc_Ctr});
}
class _AddDataState extends State<AddData> {
// Creating a TextEditingController for two Fiends,
//one is for title TextField and second is for Description TextField.
TextEditingController titleCtr = TextEditingController();
TextEditingController descCtr = TextEditingController();
// Creating a Method for Passing a data to back page.
OnPressed(BuildContext context) {
var data = Method(title_Ctr: titleCtr.text, desc_Ctr: descCtr.text);
Navigator.pop(context, data);
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(title: Text("Add Data")),
body: Form(child: Builder(builder: (context) {
return Column(children: [
TextFormField(
controller: titleCtr,
decoration: InputDecoration(hintText: "title"),
validator: (value) {
var newValue = value ?? "";
if (newValue.isEmpty) {
return 'title is Required';
}
return null;
},
),
TextFormField(
controller: descCtr,
decoration: InputDecoration(hintText: "Description"),
validator: (value) {
var newValue = value ?? "";
if (newValue.isEmpty) {
return 'Discription is Required';
}
return null;
},
),
MaterialButton(
color: Colors.red,
onPressed: () {
if (Form.of(context)?.validate() ?? false) {
OnPressed(context);
}
},
child: Text("Save"),
)
]);
})));
}
}
screenshot
1) From where you want to push :
onPressed: () async {
await Navigator.pushNamed(context, '/edit',
arguments: userData);
setState(() {
userData = userData;
});}
2) From Where you want to pop :
void updateData() async{
WorldTime instance = locations;
await instance.getData();
Navigator.pop(context, userData);
}
If you use get package then try this . passing data with get package
check get package package link
Here's another approach.
Nothing wrong with the other answers. I've tried all of the methods mentioned using global wide widgets like provider, third-party solutions, Navigator arguments, etc. This approach differs by allowing one to chain calls and pass precise data of any type required to the widget using it. We can also gain access to a completion handler event and can use this technique without being constrained to Navigator objects.
Here's the tldr:
tldr; We have to turn our thinking on its head a bit. Data can be
passed to the called widget when you navigate to it by using final
arguments with default values in the destination widget. Using an
optional function you can get data back from the 'child' (destination)
widget.
The complete explanation can be found using this SO answer., (Gist)
I just want to be here to help that 1% who might go through what I did Lol
Don't forget to put an "await" infront of "Navigator.push" in the first page,
otherwise no data will be returned to the first page when you pop from the second page...
Passing Data to back screen flutter
First Screen
final result = await Navigator.of(context).push(MaterialPageRoute(builder: (context)=>const PaymentScreen()));
Second Screen
String selected = "Credit/Debit";
Navigator.pop(context,selected);
How would I properly access the _runThisFunction(...) within the onTap()?
...
class _DealList extends State<DealList> with AutomaticKeepAliveClientMixin {
void _runThisFunction() async {
print('Run me')
}
#override
Widget build(BuildContext context) {
super.build(context);
return FutureBuilder(
future: _loadingDeals,
builder: (BuildContext context, AsyncSnapshot snapshot) {
return snapshot.connectionState == ConnectionState.done
? RefreshIndicator(
onRefresh: _handleRefresh,
child: ListView.builder(
physics: const AlwaysScrollableScrollPhysics(),
itemCount: snapshot.data['deals'].length,
itemBuilder: (context, index) {
final Map deal = snapshot.data['deals'][index];
return _getDealItem(deal, context);
},
),
)
: Center(
child: CircularProgressIndicator(),
);
},
);
}
}
Container _getDealItem(Map deal, context) {
return new Container(
height: 90.0,
child: Material(
child: InkWell(
child: _getDealRow(deal), // <-- this renders the row with the `deal` object
onTap: () {
// Below call fails
// 'The function isn't defined'
_runThisFunction();
},
),
),
);
}
The reason for that is that you are out of scope.
Little hint: The word "function" always indicates that the function you are trying to call is not part of a class and the keyword "method" shows you that the function you are trying to call is part of a class.
In your case, _runThisFunction is defined inside of _DealList, but you are trying to call it from outside.
You either need to move _getDealItem into _DealList or _runThisFunction out.
/// In this case both methods [_runThisFunction()] and [_getDealItem()] are defined inside [_DealList].
class _DealList extends State<DealList> with AutomaticKeepAliveClientMixin {
void _runThisFunction() ...
Container _getDealItem() ...
}
/// In this case both functions are defined globally.
void _runThisFunction() ...
Container _getDealItem() ...
You wil need to make sure that you also apply the same logic to _getDealRow and other nested calls.
Ok I'm pretty new to flutter/ dart so go easy on me. I'm just trying to make a very simple app where when you press a button some text updates telling you how many times you have pressed the button. I have no idea why this code doesn't work. The button appears but nothing happens when you press it.
import 'package:flutter/material.dart';
class Homepage extends StatelessWidget {
#override
Widget build(BuildContext context) {
return new Column(
children: <Widget>[],
);
}
}
class Buttonz extends StatefulWidget {
#override
_ButtonBeingPressed createState() => new _ButtonBeingPressed();
}
class _ButtonBeingPressed extends State<Buttonz> {
int _timesPressed = 0;
_buttonWasPressed() {
setState(() {
_timesPressed++;
});
}
#override
Widget build(BuildContext context) {
return new Column(children: <Widget>[
new Center(
child: new Row(
children: <Widget>[
new Text(
'The button was pressed ' + _timesPressed.toString() + "
times"),
new RaisedButton(
onPressed: _buttonWasPressed(),
child: new Row(
children: <Widget>[new Text("Press meh")],
),
),
],
))
]);
}
}
Your problem is that you didn't pass a callback to RaisedButton, you invoked your callback.
new RaisedButton(
onPressed: _buttonWasPressed(), // invokes function
child: new Row(children: <Widget>[new Text("Press meh")]),
);
To pass a callback to another widget you have two choices:
Pass a tear-off
new RaisedButton(
onPressed: _buttonWasPressed, // no `()`,
child: ...
)
Pass a closure
new RaisedButton(
onPressed: () {
// do something.
},
..
)
in some cases, this can occur with a widget in the stack.
It is possible that the Widget is overwritten with another Widget, so it cannot be clicked.
Added a Material App and rewired the RaisedButton a little. I think it was how you had onPressed wired up.
import 'package:flutter/material.dart';
void main() => runApp(new MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return new MaterialApp(home: new Buttonz());
}
}
class Buttonz extends StatefulWidget {
#override
_ButtonBeingPressed createState() => new _ButtonBeingPressed();
}
class _ButtonBeingPressed extends State<Buttonz> {
int _timesPressed = 0;
_buttonWasPressed() {
setState(() {
_timesPressed++;
});
}
#override
Widget build(BuildContext context) {
return new Column(
children: <Widget>[
new Text(
'The button was pressed $_timesPressed times'),
new RaisedButton(
child: const Text('Press meh'),
onPressed: () {
_buttonWasPressed();
},
),
],
);
}
}
Your button should be like this.:
new RaisedButton(
child: const Text('Press meh'),
onPressed: _buttonWasPressed,
),
If this doesn't work, then try to clean your flutter project with flutter clean and then reinstalling the app on debug device.
I've the below custom widget that make a Switch and reads its status (true/false)
Then I add this one to my main app widget (parent), how can I make the parent knows the value of the switch!
import 'package:flutter/material.dart';
class Switchy extends StatefulWidget{
Switchy({Key key}) : super(key: key);
#override
State<StatefulWidget> createState() => new _SwitchyState();
}
class _SwitchyState extends State<Switchy> {
var myvalue = true;
void onchange(bool value) {
setState(() {
this.myvalue = value; // I need the parent to receive this one!
print('value is: $value');
});
}
#override
Widget build(BuildContext context) {
return
new Card(
child: new Container(
child: new Row(
mainAxisAlignment: MainAxisAlignment.end,
children: <Widget>[
new Text("Enable/Disable the app in the background",
textAlign: TextAlign.left,
textDirection: TextDirection.ltr,),
new Switch(value: myvalue, onChanged: (bool value) => onchange(value)),
],
),
),
);
}
}
In the main.dart (parent) file, I started with this:
import 'widgets.dart';
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.deepOrange,
),
home: new MyHomePage(title: 'My App settup'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => new _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
Widget e = new Switchy();
//...
}
The first possibility is to pass a callback into your child, and the second is to use the of pattern for your stateful widget. See below.
import 'package:flutter/material.dart';
class MyStatefulWidget extends StatefulWidget {
#override
State<StatefulWidget> createState() => new MyStatefulWidgetState();
// note: updated as context.ancestorStateOfType is now deprecated
static MyStatefulWidgetState of(BuildContext context) =>
context.findAncestorStateOfType<MyStatefulWidgetState>();
}
class MyStatefulWidgetState extends State<MyStatefulWidget> {
String _string = "Not set yet";
set string(String value) => setState(() => _string = value);
#override
Widget build(BuildContext context) {
return new Column(
children: <Widget>[
new Text(_string),
new MyChildClass(callback: (val) => setState(() => _string = val))
],
);
}
}
typedef void StringCallback(String val);
class MyChildClass extends StatelessWidget {
final StringCallback callback;
MyChildClass({this.callback});
#override
Widget build(BuildContext context) {
return new Column(
children: <Widget>[
new FlatButton(
onPressed: () {
callback("String from method 1");
},
child: new Text("Method 1"),
),
new FlatButton(
onPressed: () {
MyStatefulWidget.of(context).string = "String from method 2";
},
child: new Text("Method 2"),
)
],
);
}
}
void main() => runApp(
new MaterialApp(
builder: (context, child) => new SafeArea(child: new Material(color: Colors.white, child: child)),
home: new MyStatefulWidget(),
),
);
There is also the alternative of using an InheritedWidget instead of a StatefulWidget; this is particularly useful if you want your child widgets to rebuild if the parent widget's data changes and the parent isn't a direct parent. See the inherited widget documentation
In 2020, the function in the highest voted answer is marked deprecated. So here is the modified solution based on that answer.
import 'package:flutter/material.dart';
class MyStatefulWidget extends StatefulWidget {
#override
State<StatefulWidget> createState() => new MyStatefulWidgetState();
// --> NOTE this! <--
static MyStatefulWidgetState of(BuildContext context) =>
context.findAncestorStateOfType<MyStatefulWidgetState>();
}
class MyStatefulWidgetState extends State<MyStatefulWidget> {
String _string = "Not set yet";
set string(String value) => setState(() => _string = value);
#override
Widget build(BuildContext context) {
return new Column(
children: <Widget>[
new Text(_string),
new MyChildClass(callback: (val) => setState(() => _string = val))
],
);
}
}
typedef void StringCallback(String val);
class MyChildClass extends StatelessWidget {
final StringCallback callback;
MyChildClass({this.callback});
#override
Widget build(BuildContext context) {
return new Column(
children: <Widget>[
new FlatButton(
onPressed: () {
callback("String from method 1");
},
child: new Text("Method 1"),
),
new FlatButton(
onPressed: () {
MyStatefulWidget.of(context).string = "String from method 2";
},
child: new Text("Method 2"),
)
],
);
}
}
void main() => runApp(
new MaterialApp(
builder: (context, child) => new SafeArea(child: new Material(color: Colors.white, child: child)),
home: new MyStatefulWidget(),
),
);
However, the methods mentioned in the answers of this question has a drawback. From doc:
In general, though, consider using a callback that triggers a stateful change in the ancestor rather than using the imperative style implied by this method. This will usually lead to more maintainable and reusable code since it decouples widgets from each other.
Calling this method is relatively expensive (O(N) in the depth of the tree). Only call this method if the distance from this widget to the desired ancestor is known to be small and bounded.
I think notifications are quite a civilized solution and they allow for a very clean communication without variable juggling and they bubble up if you need them to:
Define a notification:
class SwitchChanged extends Notification {
final bool val
SwitchChanged(this.val);
}
Raise notification in your child's event handler:
onPressed: () {
SwitchChanged(true).dispatch(context);
}
Finally, wrap your parent with notification listener:
NotificationListener<SwitchChanged>(
child: YourParent(...),
onNotification: (n) {
setState(() {
// Trigger action on parent via setState or do whatever you like.
});
return true;
}
)
You can pass a callback defined in the parent widget to the child widget and as soon as an action is performed in the child widget, the callback gets invoked.
class ParentWidget extends StatelessWidget {
// This gets called when the button is pressed in the ChildWidget.
void _onData(String data) {
print(data); // Hello World
}
#override
Widget build(BuildContext context) {
return Scaffold(
body: ChildWidget(onData: _onData),
);
}
}
class ChildWidget extends StatelessWidget {
final void Function(String) onData;
ChildWidget({
super.key,
required this.onData,
});
#override
Widget build(BuildContext context) {
return ElevatedButton(
onPressed: () {
// Pass 'Hello World' to parent widget.
onData('Hello World');
},
child: Text('Button'),
);
}
}
Use InheritedWidget - https://api.flutter.dev/flutter/widgets/InheritedWidget-class.html
This lets you access data of the parent in all the children
I found a way to do this which was fairly simple, I'm a flutter noob so maybe it isn't the best way. If someone sees something wrong with it, feel free to leave a comment. Basically state is set in parent widget, child widget updates the state of the parent, and any child widgets of the parents which use the state values are redrawn when the value is updated.
Parent widget:
class MyWidget extends StatefulWidget {
const MyWidget({Key? key}) : super(key: key);
#override
_MyWidgetState createState() => _MyWidgetState();
}
class _MyWidgetState extends State<MyWidget> {
String _stringToChange = ""; // the string you want to update in child
// function to update state with changes to term
_updateStringToChange(String stringToChange) {
setState(() {
_stringToChange = stringToChange;
// Other logic you might want to do as string value changes
});
}
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'title',
theme: ThemeData(
primarySwatch: Colors.blue,
visualDensity: VisualDensity.adaptivePlatformDensity,
),
home: Scaffold(
appBar: AppBar(
title: const Center(
child: Text("app bar title"),
),
),
body: Column(children: <Widget>[
ChildWhichMakesChanges(
updateStringToChange: _updateStringToChange,
),
Expanded(
child: Container(
padding: const EdgeInsets.fromLTRB(20, 10, 0, 10),
child: ChildWhichUsesChanges(
stringToChange: _stringToChange,
)))
]),
));
}
}
ChildWhichMakesChanges (this example uses a text box to enter input):
class ChildWhichMakesChanges extends StatefulWidget {
final ValueChanged<String> updateStringToChange;
const ChildWhichMakesChanges({Key? key, required this.updateStringToChange}) : super(key: key);
#override
_TextInputState createState() => _TextInputState();
}
class _TextInputState extends State<ChildWhichMakesChanges> {
#override
Widget build(BuildContext context) {
return Column(
crossAxisAlignment: CrossAxisAlignment.start,
mainAxisSize: MainAxisSize.min,
children: [
Padding(
padding: const EdgeInsets.symmetric(horizontal: 8, vertical: 25),
child: TextField(
decoration: const InputDecoration(
border: OutlineInputBorder(),
hintText: 'Enter text',
),
onChanged: (String stringToChange) {
widget.updateStringToChange(stringToChange);
})),
]);
}
}
Using the changed string value in ChildWhichUsesChanges:
class ChildWhichUsesChanges extends StatelessWidget {
final String stringToChange;
const ChildWhichUsesChanges(
{Key? key,
required this.stringToChange})
: super(key: key);
#override
Widget build(BuildContext context) {
return Text(stringToChange)
}
}
2022 Solution:
A simple one.
Make it work like interface.
You can make your own custom CallBack Function just by defining typedef. It will just work as an interface between child to parent widget.
This is an IMP function:
typedef void GetColor(Color? color, String? string);
Following is Parent Widget:
import 'package:flutter/material.dart';
typedef void GetColor(Color? color, String? string);
class NavigationDialog extends StatefulWidget {
const NavigationDialog({Key? key}) : super(key: key);
#override
_NavigationDialogState createState() => _NavigationDialogState();
}
class _NavigationDialogState extends State<NavigationDialog> {
Color? color = Colors.blue[700];
#override
Widget build(BuildContext context) {
return Scaffold(
backgroundColor: color,
appBar: AppBar(
title: const Text('Navigation Dialog Screen'),
),
body: Center(
child: ElevatedButton(
child: const Text('Change Color'),
onPressed: () {
_showColorDialog(context, (value, string) {
setState(() {
color = value;
print(string);
});
});
}),
),
);
}
And Following is a child Widget Code:
_showColorDialog(BuildContext context, Function getColor) async {
color = null;
await showDialog(
barrierDismissible: false,
context: context,
builder: (_) {
return AlertDialog(
title: const Text('Very important question'),
content: const Text('Please choose a color'),
actions: <Widget>[
TextButton(
child: const Text('Red'),
onPressed: () {
color = Colors.red[700];
getColor(color, 'Red');// This line of action wil send your data back to parent
Navigator.pop(context, color);
}),
TextButton(
child: const Text('Green'),
onPressed: () {
color = Colors.green[700];
getColor(color, 'Green');// This line of action wil send your data back to parent
Navigator.pop(context, color);
}),
TextButton(
child: const Text('Blue'),
onPressed: () {
color = Colors.blue[700];
getColor(color, 'Blue');// This line of action wil send your data back to parent
Navigator.pop(context, color);
}),
],
);
},
);
}
}
In this example, We are selecting a color from Child Alert Dialog widget and pass to Parent widget.
Store the value in that child widget in shared preference, then access that shared preference value in the parent widget.