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();
}
...
}
Related
Currently, when I would like initial values of a stateful widget to be configurable, I follow a pattern that looks like
class MyWidget extends StatefulWidget {
final String? initialValue;
MyWidget({ this.initialValue });
#override State createState() => MyWidgetState();
}
class MyWidgetState extends State<MyWidget> {
String statefulValue = "default initial value";
#override
void initState() {
super.initState();
if (widget.initialValue != null) { statefulValue = widget.initialValue; }
}
// ...
}
This works, but seems a bit heavyweight to me to achieve something I have to think is a very common use case. First, it doesn't make sense to me that initialValue should have to be a field at all, since its use is only to initialize the state, and then is no longer needed. Second, I think it would avoid some boiler plate if the state class could have a constructor that the stateful widget could call, so the above could look like:
class MyWidget extends StatefulWidget {
final String? initialValue;
MyWidget({ this.initialValue });
#override State createState() => MyWidgetState(initialValue: initialValue);
}
class MyWidgetState extends State<MyWidget> {
String statefulValue;
MyWidgetState({ String? initialValue }) : statefulValue = initialValue ?? "default initial value";
// ...
}
That doesn't exactly solve the first problem, but I think reads more easily. This however triggers the "Don't put any logic in createState" linter error. So my questions are
a) is there a pattern where the initial value doesn't have to be held on to longer than necessary?
b) why is passing parameters to the State constructor frowned upon?
You can provide default value on constructor
class MyWidget extends StatefulWidget {
final String initialValue;
const MyWidget({this.initialValue = "default initial value"});
#override
State<MyWidget> createState() => _MyWidgetState();
}
class _MyWidgetState extends State<MyWidget> {
late String statefulValue = widget.initialValue;
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 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();
}
}
class Notice extends StatefulWidget {
final String s_id;
const Notice({Key key, this.s_id}) : super(key: key);
#override
_NoticeState createState() => _NoticeState();
}
class _NoticeState extends State<Notice> {
TextEditingController _titleController = new TextEditingController();
var api =
Uri.parse('https://www.a2rstore.in/api/school/v1/noticeApi.php?id=${widget.s_id}');
You can't call the "widget" without the context.
The proper way to do it is by first defining your variable:
class _NoticeState extends State<Notice> {
TextEditingController _titleController = new TextEditingController();
var api;
...
}
And then assigning to it the value either in the build or initState method:
#override
initState(){
api = Uri.parse('https://www.a2rstore.in/api/school/v1/noticeApi.php?id=${widget.s_id}');
}