Related
I'm making an image gallery and I need the user to be able to long-press an image to show a popup menu which will let him delete the image.
My code, so far:
return GestureDetector(
onLongPress: () {
showMenu(
items: <PopupMenuEntry>[
PopupMenuItem(
value: this._index,
child: Row(
children: <Widget>[
Icon(Icons.delete),
Text("Delete"),
],
),
)
],
context: context,
);
},
child: Image.memory(
this._asset.thumbData.buffer.asUint8List(),
fit: BoxFit.cover,
gaplessPlayback: true,
),
);
Which produces:
But also, I couldn't find out how to completely remove the image's widget when the longPress function is called. How to do so?
The OP and the First Answerer bypassed the original problem using PopupMenuButton, which worked fine in their case. But I think the more general question of how to position one's own menu and how to receive the user's response without using PopupMenuButton is worth answering, because sometimes we want a popup menu on a custom widget, and we want it to appear on some gestures other than a simple tap (e.g. the OP's original intention was to long-press).
I set out to make a simple app demonstrating the following:
Use a GestureDetector to capture long-press
Use the function showMenu() to display a popup menu, and position it near the finger's touch
How to receive the user's selection
(Bonus) How to make a PopupMenuEntry that represents multiple values (the oft-used PopupMenuItem can only represent a single value)
The result is, when you long-press on a big yellow area, a popup menu appears on which you can select +1 or -1, and the big number would increment or decrement accordingly:
Skip to the end for the entire body of code. Comments are sprinkled in there to explain what I am doing. Here are a few things to note:
showMenu()'s position parameter takes some effort to understand. It's a RelativeRect, which represents how a smaller rect is positioned inside a bigger rect. In our case, the bigger rect is the entire screen, the smaller rect is the area of touch. Flutter positions the popup menu according to these rules (in plain English):
if the smaller rect leans toward the left half of the bigger rect, the popup menu would align with the smaller rect's left edge
if the smaller rect leans toward the right half of the bigger rect, the popup menu would align with the smaller rect's right edge
if the smaller rect is in the middle, which edge wins depends on the language's text direction. Left edge wins if using English and other left-to-right languages, right edge wins otherwise.
It's always useful to reference PopupMenuButton's official implementation to see how it uses showMenu() to display the menu.
showMenu() returns a Future. Use Future.then() to register a callback to handle user selection. Another option is to use await.
Remember that PopupMenuEntry is a (subclass of) StatefulWidget. You can layout any number of sub-widgets inside it. This is how you represent multiple values in a PopupMenuEntry. If you want it to represent two values, just make it contain two buttons, however you want to lay them out.
To close the popup menu, use Navigator.pop(). Flutter treats popup menus like a smaller "page". When we display a popup menu, we are actually pushing a "page" to the navigator's stack. To close a popup menu, we pop it from the stack, thus completing the aforementioned Future.
Here is the full code:
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Popup Menu Usage',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(title: 'Popup Menu Usage'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
var _count = 0;
var _tapPosition;
void _showCustomMenu() {
final RenderBox overlay = Overlay.of(context).context.findRenderObject();
showMenu(
context: context,
items: <PopupMenuEntry<int>>[PlusMinusEntry()],
position: RelativeRect.fromRect(
_tapPosition & const Size(40, 40), // smaller rect, the touch area
Offset.zero & overlay.size // Bigger rect, the entire screen
)
)
// This is how you handle user selection
.then<void>((int delta) {
// delta would be null if user taps on outside the popup menu
// (causing it to close without making selection)
if (delta == null) return;
setState(() {
_count = _count + delta;
});
});
// Another option:
//
// final delta = await showMenu(...);
//
// Then process `delta` however you want.
// Remember to make the surrounding function `async`, that is:
//
// void _showCustomMenu() async { ... }
}
void _storePosition(TapDownDetails details) {
_tapPosition = details.globalPosition;
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
GestureDetector(
// This does not give the tap position ...
onLongPress: _showCustomMenu,
// Have to remember it on tap-down.
onTapDown: _storePosition,
child: Container(
color: Colors.amberAccent,
padding: const EdgeInsets.all(100.0),
child: Text(
'$_count',
style: const TextStyle(
fontSize: 100, fontWeight: FontWeight.bold),
),
),
),
],
),
),
);
}
}
class PlusMinusEntry extends PopupMenuEntry<int> {
#override
double height = 100;
// height doesn't matter, as long as we are not giving
// initialValue to showMenu().
#override
bool represents(int n) => n == 1 || n == -1;
#override
PlusMinusEntryState createState() => PlusMinusEntryState();
}
class PlusMinusEntryState extends State<PlusMinusEntry> {
void _plus1() {
// This is how you close the popup menu and return user selection.
Navigator.pop<int>(context, 1);
}
void _minus1() {
Navigator.pop<int>(context, -1);
}
#override
Widget build(BuildContext context) {
return Row(
children: <Widget>[
Expanded(child: FlatButton(onPressed: _plus1, child: Text('+1'))),
Expanded(child: FlatButton(onPressed: _minus1, child: Text('-1'))),
],
);
}
}
If you are going to use a gridView or listview for laying out the images on the screen, you can wrap each item with a gesture detector then you should keep your images in a list somewhere, then simply remove the image from the list and call setState().
Something like the following. (This code will probably won't compile but it should give you the idea)
ListView.builder(
itemCount: imageList.length,
itemBuilder: (BuildContext context, int index) {
return GestureDetector(
onLongPress: () {
showMenu(
onSelected: () => setState(() => imageList.remove(index))}
items: <PopupMenuEntry>[
PopupMenuItem(
value: this._index,
child: Row(
children: <Widget>[
Icon(Icons.delete),
Text("Delete"),
],
),
)
],
context: context,
);
},
child: imageList[index],
);
}
)
Edit: You can use a popup menu too, like following
Container(
margin: EdgeInsets.symmetric(vertical: 10),
height: 100,
width: 100,
child: PopupMenuButton(
child: FlutterLogo(),
itemBuilder: (context) {
return <PopupMenuItem>[new PopupMenuItem(child: Text('Delete'))];
},
),
),
Building on the answers by Nick Lee and hacker1024, but instead of turning the solution into a mixin, you could simply just turn it into a widget:
class PopupMenuContainer<T> extends StatefulWidget {
final Widget child;
final List<PopupMenuEntry<T>> items;
final void Function(T) onItemSelected;
PopupMenuContainer({#required this.child, #required this.items, #required this.onItemSelected, Key key}) : super(key: key);
#override
State<StatefulWidget> createState() => PopupMenuContainerState<T>();
}
class PopupMenuContainerState<T> extends State<PopupMenuContainer<T>>{
Offset _tapDownPosition;
#override
Widget build(BuildContext context) {
return GestureDetector(
onTapDown: (TapDownDetails details){
_tapDownPosition = details.globalPosition;
},
onLongPress: () async {
final RenderBox overlay = Overlay.of(context).context.findRenderObject();
T value = await showMenu<T>(
context: context,
items: widget.items,
position: RelativeRect.fromLTRB(
_tapDownPosition.dx,
_tapDownPosition.dy,
overlay.size.width - _tapDownPosition.dx,
overlay.size.height - _tapDownPosition.dy,
),
);
widget.onItemSelected(value);
},
child: widget.child
);
}
}
And then you'd use it like this:
child: PopupMenuContainer<String>(
child: Image.asset('assets/image.png'),
items: [
PopupMenuItem(value: 'delete', child: Text('Delete'))
],
onItemSelected: (value) async {
if( value == 'delete' ){
await showDialog(context: context, child: AlertDialog(
title: Text('Delete image'),
content: Text('Are you sure you want to delete the image?'),
actions: [
uiFlatButton(child: Text('NO'), onTap: (){ Navigator.of(context).pop(false); }),
uiFlatButton(child: Text('YES'), onTap: (){ Navigator.of(context).pop(true); }),
],
));
}
},
),
Adjust the code to fit your needs.
Nick Lee's answer can be turned into a mixin quite easily, which can then be used anywhere you want to use a popup menu.
The mixin:
import 'package:flutter/material.dart' hide showMenu;
import 'package:flutter/material.dart' as material show showMenu;
/// A mixin to provide convenience methods to record a tap position and show a popup menu.
mixin CustomPopupMenu<T extends StatefulWidget> on State<T> {
Offset _tapPosition;
/// Pass this method to an onTapDown parameter to record the tap position.
void storePosition(TapDownDetails details) => _tapPosition = details.globalPosition;
/// Use this method to show the menu.
Future<T> showMenu<T>({
#required BuildContext context,
#required List<PopupMenuEntry<T>> items,
T initialValue,
double elevation,
String semanticLabel,
ShapeBorder shape,
Color color,
bool captureInheritedThemes = true,
bool useRootNavigator = false,
}) {
final RenderBox overlay = Overlay.of(context).context.findRenderObject();
return material.showMenu<T>(
context: context,
position: RelativeRect.fromLTRB(
_tapPosition.dx,
_tapPosition.dy,
overlay.size.width - _tapPosition.dx,
overlay.size.height - _tapPosition.dy,
),
items: items,
initialValue: initialValue,
elevation: elevation,
semanticLabel: semanticLabel,
shape: shape,
color: color,
captureInheritedThemes: captureInheritedThemes,
useRootNavigator: useRootNavigator,
);
}
}
And then, to use it:
import 'package:flutter/material.dart';
import './custom_context_menu.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Popup Menu Usage',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(title: 'Popup Menu Usage'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> with CustomPopupMenu {
var _count = 0;
void _showCustomMenu() {
this.showMenu(
context: context,
items: <PopupMenuEntry<int>>[PlusMinusEntry()],
)
// This is how you handle user selection
.then<void>((int delta) {
// delta would be null if user taps on outside the popup menu
// (causing it to close without making selection)
if (delta == null) return;
setState(() {
_count = _count + delta;
});
});
// Another option:
//
// final delta = await showMenu(...);
//
// Then process `delta` however you want.
// Remember to make the surrounding function `async`, that is:
//
// void _showCustomMenu() async { ... }
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
GestureDetector(
// This does not give the tap position ...
onLongPress: _showCustomMenu,
// Have to remember it on tap-down.
onTapDown: storePosition,
child: Container(
color: Colors.amberAccent,
padding: const EdgeInsets.all(100.0),
child: Text(
'$_count',
style: const TextStyle(fontSize: 100, fontWeight: FontWeight.bold),
),
),
),
],
),
),
);
}
}
class PlusMinusEntry extends PopupMenuEntry<int> {
#override
double height = 100;
// height doesn't matter, as long as we are not giving
// initialValue to showMenu().
#override
bool represents(int n) => n == 1 || n == -1;
#override
PlusMinusEntryState createState() => PlusMinusEntryState();
}
class PlusMinusEntryState extends State<PlusMinusEntry> {
void _plus1() {
// This is how you close the popup menu and return user selection.
Navigator.pop<int>(context, 1);
}
void _minus1() {
Navigator.pop<int>(context, -1);
}
#override
Widget build(BuildContext context) {
return Row(
children: <Widget>[
Expanded(child: FlatButton(onPressed: _plus1, child: Text('+1'))),
Expanded(child: FlatButton(onPressed: _minus1, child: Text('-1'))),
],
);
}
}
Answer for 2023
In Flutter 3.7 there is now a ContextMenuRegion widget that you can wrap around any existing widget. When the user long presses or right-clicks (depending on the platform), the menu you give it will appear.
return Scaffold(
body: Center(
child: ContextMenuRegion(
contextMenuBuilder: (context, offset) {
return AdaptiveTextSelectionToolbar.buttonItems(
anchors: TextSelectionToolbarAnchors(
primaryAnchor: offset,
),
buttonItems: <ContextMenuButtonItem>[
ContextMenuButtonItem(
onPressed: () {
ContextMenuController.removeAny();
},
label: 'Save',
),
],
);
},
child: const SizedBox(
width: 200.0,
height: 200.0,
child: FlutterLogo(),
),
),
),
);
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);
Here is my code, I've created an ExpansionTile and it has a child TextFormField.
import 'package:flutter/material.dart';
class OrderCreatePage extends StatefulWidget {
#override
_OrderCreatePageState createState() => _OrderCreatePageState();
}
class _OrderCreatePageState extends State<OrderCreatePage> {
String _userID;
TextEditingController _controllerl;
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: new Text("Create"),
),
body: ExpansionTile(
title: Text("Create"),
children: <Widget>[
TextFormField(
decoration: InputDecoration(
labelText: "User ID",
icon: Icon(Icons.face),
),
validator: (val) {},
controller: _controllerl,
onSaved: (val) => _userID = val,
)
],
),
);
}
}
Whenever I type something into the TextFormField and collapse the ExpansionTile, the data in the TextFormField is lost. I'm using this type of UI because I have to create a big form getting a lot of details. If there is no ExpansionTile, then the user has to scroll a long way.
As mentioned by - #pskink
In your Code Add under TextEditingController _controllerl; :
#override
void initState() {
super.initState();
_controllerl = TextEditingController();
}
So your Code will look like :
class _OrderCreatePageState extends State<OrderCreatePage> {
String _userID;
TextEditingController _controllerl;
#override
void initState() {
super.initState();
_controllerl = TextEditingController();
}
#override
Widget build(BuildContext context) {
return Scaffold(
....
......
https://api.flutter.dev/flutter/material/ExpansionTile/maintainState.html
ExpansionTile(maintainState: true, title: Text("text here"), ...
With this, the state of the children will be maintained after collapsing and opening.
I assume you use some sort of ScrollView to display the input fields.
The following is stated in the ExpansionTile reference:
This widget is typically used with ListView to create an "expand /
collapse" list entry. When used with scrolling widgets like ListView,
a unique PageStorageKey must be specified to enable the ExpansionTile
to save and restore its expanded state when it is scrolled in and out
of view.
So adding a PageStorageKey should do the trick:
ExpansionTile(
key: PageStorageKey('myInputField'),
title: Text("Create"),
children: <Widget>[
TextFormField(
decoration: InputDecoration(
labelText: "User ID",
icon: Icon(Icons.face),
),
validator: (val) {},
controller: _controllerl,
onSaved: (val) => _userID = val,
)
],
)
I have a list of stateful widgets where the user can add, remove, and interact with items in the list. Removing items from the list causes subsequent items in the list to rebuild as they shift to fill the deleted row. This results in a loss of state data for these widgets - though they should remain unaltered other than their location on the screen. I want to be able to maintain state for the remaining items in the list even as their position changes.
Below is a simplified version of my app which consists primarily of a list of StatefulWidgets. The user can add items to the list ("tasks" in my app) via the floating action button or remove them by swiping. Any item in the list can be highlighted by tapping the item, which changes the state of the background color of the item. If multiple items are highlighted in the list, and an item (other than the last item in the list) is removed, the items that shift to replace the removed item lose their state data (i.e. the background color resets to transparent). I suspect this is because _taskList rebuilds since I call setState() to update the display after a task is removed. I want to know if there is a clean way to maintain state data for the remaining tasks after a task is removed from _taskList.
void main() => runApp(new TimeTrackApp());
class TimeTrackApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'Time Tracker',
theme: new ThemeData(
primarySwatch: Colors.blue,
),
home: new TimeTrackHome(title: 'Task List'),
);
}
}
class TimeTrackHome extends StatefulWidget {
TimeTrackHome({Key key, this.title}) : super(key: key);
final String title;
#override
_TimeTrackHomeState createState() => new _TimeTrackHomeState();
}
class _TimeTrackHomeState extends State<TimeTrackHome> {
TextEditingController _textController;
List<TaskItem> _taskList = new List<TaskItem>();
void _addTaskDialog() async {
_textController = TextEditingController();
await showDialog(
context: context,
builder: (_) => new AlertDialog(
title: new Text("Add A New Task"),
content: new TextField(
controller: _textController,
decoration: InputDecoration(
border: InputBorder.none, hintText: 'Enter the task name'),
),
actions: <Widget>[
new FlatButton(
onPressed: () => Navigator.pop(context),
child: const Text("CANCEL")),
new FlatButton(
onPressed: (() {
Navigator.pop(context);
_addTask(_textController.text);
}),
child: const Text("ADD"))
],
));
}
void _addTask(String title) {
setState(() {
// add the new task
_taskList.add(TaskItem(
name: title,
));
});
}
#override
void initState() {
_taskList = List<TaskItem>();
super.initState();
}
#override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text(widget.title),
),
body: new Align(
alignment: Alignment.topCenter,
child: ListView.builder(
padding: EdgeInsets.all(0.0),
itemExtent: 60.0,
itemCount: _taskList.length,
itemBuilder: (BuildContext context, int index) {
if (index < _taskList.length) {
return Dismissible(
key: ObjectKey(_taskList[index]),
onDismissed: (direction) {
if(this.mounted) {
setState(() {
_taskList.removeAt(index);
});
}
},
child: _taskList[index],
);
}
}),
),
floatingActionButton: new FloatingActionButton(
onPressed: _addTaskDialog,
tooltip: 'Click to add a new task',
child: new Icon(Icons.add),
),
);
}
}
class TaskItem extends StatefulWidget {
final String name;
TaskItem({Key key, this.name}) : super(key: key);
TaskItem.from(TaskItem other) : name = other.name;
#override
State<StatefulWidget> createState() => new _TaskState();
}
class _TaskState extends State<TaskItem> {
static final _taskFont =
const TextStyle(fontSize: 26.0, fontWeight: FontWeight.bold);
Color _color = Colors.transparent;
void _highlightTask() {
setState(() {
if(_color == Colors.transparent) {
_color = Colors.greenAccent;
}
else {
_color = Colors.transparent;
}
});
}
#override
Widget build(BuildContext context) {
return Column(children: <Widget>[
Material(
color: _color,
child: ListTile(
title: Text(
widget.name,
style: _taskFont,
textAlign: TextAlign.center,
),
onTap: () {
_highlightTask();
},
),
),
Divider(
height: 0.0,
),
]);
}
}
I ended up solving the problem by creating an intermediate class which contains a reference to the StatefulWidget and transferred over all the state variables. The State class accesses the state variables through a reference to the intermediate class. The higher level widget that contained and managed a List of the StatefulWidget now access the StatefulWidget through this intermediate class. I'm not entirely confident in the "correctness" of my solution as I haven't found any other examples of this, so I am still open to suggestions.
My intermediate class is as follows:
class TaskItemData {
// StatefulWidget reference
TaskItem widget;
Color _color = Colors.transparent;
TaskItemData({String name: "",}) {
_color = Colors.transparent;
widget = TaskItem(name: name, stateData: this,);
}
}
My StatefulWidget and its corresponding State classes are nearly unchanged, except that the state variables no longer reside in the State class. I also added a reference to the intermediate class inside my StatefulWidget which gets initialized in the constructor. Previous uses of state variables in my State class now get accessed through the reference to the intermediate class. The modified StatefulWidget and State classes is as follows:
class TaskItem extends StatefulWidget {
final String name;
// intermediate class reference
final TaskItemData stateData;
TaskItem({Key key, this.name, this.stateData}) : super(key: key);
#override
State<StatefulWidget> createState() => new _TaskItemState();
}
class _TaskItemState extends State<TaskItem> {
static final _taskFont =
const TextStyle(fontSize: 26.0, fontWeight: FontWeight.bold);
void _highlightTask() {
setState(() {
if(widget.stateData._color == Colors.transparent) {
widget.stateData._color = Colors.greenAccent;
}
else {
widget.stateData._color = Colors.transparent;
}
});
}
#override
Widget build(BuildContext context) {
return Column(children: <Widget>[
Material(
color: widget.stateData._color,
child: ListTile(
title: Text(
widget.name,
style: _taskFont,
textAlign: TextAlign.center,
),
onTap: () {
_highlightTask();
},
),
),
Divider(
height: 0.0,
),
]);
}
}
The widget containing the List of TaskItem objects has been replaced with a List of TaskItemData. The ListViewBuilder child now accesses the TaskItem widget through the intermediate class (i.e. child: _taskList[index], has changed to child: _taskList[index].widget,). It is as follows:
class _TimeTrackHomeState extends State<TimeTrackHome> {
TextEditingController _textController;
List<TaskItemData> _taskList = new List<TaskItemData>();
void _addTaskDialog() async {
_textController = TextEditingController();
await showDialog(
context: context,
builder: (_) => new AlertDialog(
title: new Text("Add A New Task"),
content: new TextField(
controller: _textController,
decoration: InputDecoration(
border: InputBorder.none, hintText: 'Enter the task name'),
),
actions: <Widget>[
new FlatButton(
onPressed: () => Navigator.pop(context),
child: const Text("CANCEL")),
new FlatButton(
onPressed: (() {
Navigator.pop(context);
_addTask(_textController.text);
}),
child: const Text("ADD"))
],
));
}
void _addTask(String title) {
setState(() {
// add the new task
_taskList.add(TaskItemData(
name: title,
));
});
}
#override
void initState() {
_taskList = List<TaskItemData>();
super.initState();
}
#override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text(widget.title),
),
body: new Align(
alignment: Alignment.topCenter,
child: ListView.builder(
padding: EdgeInsets.all(0.0),
itemExtent: 60.0,
itemCount: _taskList.length,
itemBuilder: (BuildContext context, int index) {
if (index < _taskList.length) {
return Dismissible(
key: ObjectKey(_taskList[index]),
onDismissed: (direction) {
if(this.mounted) {
setState(() {
_taskList.removeAt(index);
});
}
},
child: _taskList[index].widget,
);
}
}),
),
floatingActionButton: new FloatingActionButton(
onPressed: _addTaskDialog,
tooltip: 'Click to add a new task',
child: new Icon(Icons.add),
),
);
}
}
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.