I want a default empty controller for my custom text field but its not allowing with both ways
You cannot have a const constructor and use a non constant default value.
Therefore you would have to remove the const keyword before CustomTextField. But you can also not have a non-constant value as an optional parameter.
So a suggestion is to change the stateless widget to a stateful widget and initialize the controller in the init() method if no controller is provided with the the contructor.
It's better to set a default controller like this, so we can dispose it to prevent memory leaks:
import 'package:flutter/material.dart';
class CustomTextField extends StatefulWidget {
const CustomTextField({
Key? key,
this.controller,
}) : super(key: key);
final TextEditingController? controller;
#override
State<CustomTextField> createState() => _CustomTextFieldState();
}
class _CustomTextFieldState extends State<CustomTextField> {
late TextEditingController _controller;
#override
void initState() {
super.initState();
_controller = widget.controller ?? TextEditingController();
}
#override
void dispose() {
if (widget.controller == null) {
// if we made the controller ourselves, we dispose it ourselves
// but if it's made outside of this widget, it should be disposed outside
_controller.dispose();
}
super.dispose();
}
#override
Widget build(BuildContext context) {
return Container();
}
}
Related
I got a ListView.builder that generates n number of elements and I am looking at adding a controller for each of them. I have seen some approaches of adding a controller to a list of controllers and then access them by the index however I am just wondering how will this impact the performance of the screen if lets say you have 20 controllers? Are there some best practices for this scenario? Should you even go down this line or avoid it?
I suggest to introduce a Widget for all items in list.
Make sure you dispose in a correct place for the performance.
Also I request to store the user entered value with the object of item will help to restore on scrolls.
Eg:
class YourWidget extends StatefulWidget {
const YourWidget({Key? key, required this.item}) : super(key: key);
final YourItem item;
#override
State<YourWidget> createState() => _YourWidgetState();
}
class _YourWidgetState extends State<YourWidget> {
final controller = TextEditingController();
#override
void initState() {
super.initState();
controller.text = widget.item.enteredValue;
}
#override
Widget build(BuildContext context) {
return TextField(
controller: controller,
onChanged: (value){
widget.item.enteredValue = value;
},
...
);
}
#override
void dispose() {
controller.dispose();
super.dispose();
}
}
class YourItem {
String? id;
...
String enteredValue = '';
}
I am new in flutter and i have some codes to build textfield. i want to make an initial value in textfield but this is from input in another class.
class TextFieldEdit extends StatefulWidget {
TextFieldEdit({
Key? key,
required this.title,
required this.hintTxt,
required this.controller,
required this.defaultTxt,
}) : super(key: key);
final String title, hintTxt;
final controller;
final defaultTxt;
#override
State<TextFieldEdit> createState() => _TextFieldEditState();
}
class _TextFieldEditState extends State<TextFieldEdit> {
TextEditingController _controller = TextEditingController();
#override
void initState() {
super.initState();
_controller.text = defaultTxt;
}
#override
Widget build(BuildContext context) {
return ...
}
in _TextFieldEditState class at the _controller.text i want to get value from defaultTxt in TextFieldEdit class. But how can i send it to _TextFieldEditState class?
the error message is : Undefined name 'defaultTxt'.
Try correcting the name to one that is defined, or defining the name.
Use widget. to access to the variable in constructor:
#override
void initState() {
super.initState();
_controller.text = widget.defaultTxt;
}
To access the widget variable follow widget.variableName
You can do
late final TextEditingController _controller =
TextEditingController.fromValue(
TextEditingValue(text: widget.defaultTxt));
Or use initState to assign the _controller.
I'm new to Riverpod and am trying to migrate an app over from Provider. If I had a TextField and wanted to set its value based on my Provider model, I would do this:
class MyWidget extends StatefulWidget{
const MyWidget({ Key? key }) : super(key: key);
#override
State<MyWidget> createState() => _MyWidgetState();
}
class _MyWidgetState extends State<MyWidget> {
var controller = TextEditingController();
#override
void didChangeDependencies() {
super.didChangeDependencies();
//Set the value here...
var model = Provider.of<Model>(context);
controller.text = model.name;
}
Widget build(BuildContext context) {
return TextField(controller: controller)
}
}
As I understand it, didChangeDependencies() would listen to changes from Provider.of<Model>(context) and update my controller accordingly.
I'm trying to pull off the same thing with Provider, but I can't ever get the TextField's value to show up.
class MyWidget extends ConsumerStatefulWidget {
const MyWidget({Key? key}) : super(key: key);
#override
ConsumerState<ConsumerStatefulWidget> createState() => _MyWidgetState();
}
class _MyWidgetState extends ConsumerState<MyWidget> {
var controller = TextEditingController();
#override
void didChangeDependencies() {
super.didChangeDependencies();
//Trying the same thing here...
final name = ref.watch(providerName);
controller.text = name;
}
Widget build(BuildContext context) {
final name = ref.watch(providerName);
return Column(
children: [
//This doesn't work:
TextField(controller: controller),
//I know my provider has the value, because this works fine:
Text(name),
]
}
}
How can I get my TextEditingController's text property to update?
From Riverpod official website
///1.Create a [StateNotifier] sub-class, StateNotifier is something where you can define functions that can change your state like in this state is of String type, you also can use objects (Classes instead of primitive types)
class Counter extends StateNotifier<String> {
Counter() : super('');
void changeText(String text){
state=text;
}
///2.Create a provider [StateNotifierProvider] with this you can use in your widget
final counterProvider = StateNotifierProvider<Counter, String>((ref) {
return Counter();
});
///3.Consume the Provider this is how we can attach state with our widget
class Home extends ConsumerWidget {
#override
Widget build(BuildContext context, WidgetRef ref) {
final text = ref.watch(counterProvider);
return Text('$text');
}
}
so here you can add you widget like button and onTap executes the code like
onTap()=>changeText(textController.text);
So your text [Text('$text');] will automatically change.
String inputText = controller.text;
I got a Visual Studio warning on my class (below) saying "This class (or a class which this class inherits from) is marked as '#immutable', but one or more of its instance fields are not final: UserSignIn._email", but I cannot mark this argument as final because I initialise it in the constructor
Without final :
class UserSignIn extends StatefulWidget {
TextEditingController _email;
UserSignIn({String emailInput}) {
this._email = TextEditingController(text: (emailInput ?? ""));
}
#override
_UserSignInState createState() => _UserSignInState();
}
class _UserSignInState extends State<UserSignIn> {
#override
Widget build(BuildContext context) {
...
}
}
How to do this ?
Thank you
You should put the TextEditingController in the state class and initialise it in the initState method, like this.
And keep in mind that the StatefulWidget can be different every time when the widget tree is changed, so don't put anything in there that is not immutable.
Keep everything dynamic in the State class
class UserSignIn extends StatefulWidget {
final String emailInput;
const UserSignIn({Key key, this.emailInput}) : super(key: key);
#override
_UserSignInState createState() => _UserSignInState();
}
class _UserSignInState extends State<UserSignIn> {
TextEditingController _controller;
#override
void initState() {
_controller = TextEditingController(text: widget.emailInput);
super.initState();
}
...
}
I have 2 screens in my Flutter app: a list of records and a screen for creating and editing records.
If I pass an object to the second screen that means I am going to edit this and if I pass null it means that I am creating a new item. The editing screen is a Stateful widget and I am not sure how to use this approach https://flutter.io/cookbook/navigation/passing-data/ for my case.
class RecordPage extends StatefulWidget {
final Record recordObject;
RecordPage({Key key, #required this.recordObject}) : super(key: key);
#override
_RecordPageState createState() => new _RecordPageState();
}
class _RecordPageState extends State<RecordPage> {
#override
Widget build(BuildContext context) {
//.....
}
}
How can I access recordObject inside _RecordPageState?
To use recordObject in _RecordPageState, you have to just write widget.objectname like below
class _RecordPageState extends State<RecordPage> {
#override
Widget build(BuildContext context) {
.....
widget.recordObject
.....
}
}
Full Example
You don't need to pass parameters to State using it's constructor.
You can easily access these using widget.myField.
class MyRecord extends StatefulWidget {
final String recordName;
const MyRecord(this.recordName);
#override
MyRecordState createState() => MyRecordState();
}
class MyRecordState extends State<MyRecord> {
#override
Widget build(BuildContext context) {
return Text(widget.recordName); // Here you direct access using widget
}
}
Pass your data when you Navigate screen :
Navigator.of(context).push(MaterialPageRoute(builder: (context) => MyRecord("WonderWorld")));
class RecordPage extends StatefulWidget {
final Record recordObject;
RecordPage({Key key, #required this.recordObject}) : super(key: key);
#override
_RecordPageState createState() => new _RecordPageState(recordObject);
}
class _RecordPageState extends State<RecordPage> {
Record recordObject
_RecordPageState(this. recordObject); //constructor
#override
Widget build(BuildContext context) {. //closure has access
//.....
}
}
example as below:
class nhaphangle extends StatefulWidget {
final String username;
final List<String> dshangle;// = ["1","2"];
const nhaphangle({ Key key, #required this.username,#required this.dshangle }) : super(key: key);
#override
_nhaphangleState createState() => _nhaphangleState();
}
class _nhaphangleState extends State<nhaphangle> {
TextEditingController mspController = TextEditingController();
TextEditingController soluongController = TextEditingController();
final scrollDirection = Axis.vertical;
DateTime Ngaysx = DateTime.now();
ScrollController _scrollController = new ScrollController();
ApiService _apiService;
List<String> titles = [];
#override
void initState() {
super.initState();
_apiService = ApiService();
titles = widget.dshangle; //here var is call and set to
}
I have to Navigate back to any one of the screens in the list pages but when I did that my onTap function stops working and navigation stops.
class MyBar extends StatefulWidget {
MyBar({this.pageNumber});
final pageNumber;
static const String id = 'mybar_screen';
#override
_MyBarState createState() => _MyBarState();
}
class _MyBarState extends State<MyBar> {
final List pages = [
NotificationScreen(),
AppointmentScreen(),
RequestBloodScreen(),
ProfileScreen(),
];
#override
Widget build(BuildContext context) {
var _selectedItemIndex = widget.pageNumber;
return Scaffold(
bottomNavigationBar: BottomNavigationBar(
elevation: 0,
backgroundColor: Colors.white,
unselectedItemColor: Colors.grey.shade700,
selectedItemColor: Color(kAppColor),
selectedIconTheme: IconThemeData(color: Color(kAppColor)),
currentIndex: _selectedItemIndex,
type: BottomNavigationBarType.fixed,
onTap: (int index) {
setState(() {
_selectedItemIndex = index;
});
},
You should use a Pub/Sub mechanism.
I prefer to use Rx in many situations and languages. For Dart/Flutter this is the package: https://pub.dev/packages/rxdart
For example, you can use a BehaviorSubject to emit data from widget A, pass the stream to widget B which listens for changes and applies them inside the setState.
Widget A:
// initialize subject and put it into the Widget B
BehaviorSubject<LiveOutput> subject = BehaviorSubject();
late WidgetB widgetB = WidgetB(deviceOutput: subject);
// when you have to emit new data
subject.add(deviceOutput);
Widget B:
// add stream at class level
class WidgetB extends StatefulWidget {
final ValueStream<LiveOutput> deviceOutput;
const WidgetB({Key? key, required this.deviceOutput}) : super(key: key);
#override
State<WidgetB> createState() => _WidgetBState();
}
// listen for changes
#override
void initState() {
super.initState();
widget.deviceOutput.listen((event) {
print("new live output");
setState(() {
// do whatever you want
});
});
}
In my app, often instead of using stateful widgets, I use mainly ChangeNotifierProvider<T> in main.dart, some model class
class FooModel extends ChangeNotifier {
var _foo = false;
void changeFooState() {
_foo = true;
notifyListeners();
}
bool getFoo () => _foo;
}
and
var foo = context.read<FooModel>();
# or
var foo = context.watch<FooModel>();
in my stateless widgets. IMO this gives me more precise control over the rebuilding upon runtime state change, compared to stateful widgets.
The recipe can be found in the official docs, the concept is called "lifting state up".