I have the following code, shown below where every time I make changes to a text field, a function gets called, in my case doSomething(). However, I assumed that since I bound the value of the text to a variable, if that variable were to get updated, the textfield text would also update. This is not happening, and my question is, what would be the simplest way to make the textfield update its text every time the corresponding variable changes.
Edit: Just to clarify, I have no problem getting the doSomething() function to update other parts of the code, I am looking for the inverse where an external variable changes the text of the textfield
import 'package:flutter/material.dart';
class DynamicTextField extends StatefulWidget {
const DynamicTextField(
{
required this.value,
Key? key})
: super(key: key);
final double value;
#override
State<DynamicTextField> createState() =>
_DynamicTextFieldState(value);
}
class _DynamicTextFieldState extends State<DynamicTextField> {
_DynamicTextFieldState(this.value);
final double value;
late TextEditingController textChanged;
#override
void initState() {
textChanged = TextEditingController(text: value.toString());
super.initState();
}
#override
Widget build(BuildContext context) {
return TextField(
controller: textChanged,
onChanged: (text) {
doSomething();
},
);
}
}
you can change the TextField value with the textChanged controller you set to that widget.
String stringVariable = "some value";
textChanged.text = stringVariable;
you can then update the state with a normal SetState(() {}), and it should update the value in TextField
Your value is declared as final. Meaning it can only be set once. Try removing the final declaration.
I also see you’re also declaring the value variable twice, instead of referencing the original value variable.
The second declaration should be in the widgets build method & should = widget.value.
this will update the text everytime DynamicTextField get rebuild.
#override
void initState() {
textChanged = TextEditingController(text: widget.value.toString());
super.initState();
}
Depends how you use the DynamicTextField in another class. The life-cycle of StatefullWidget is call the initState once the widget initialize.
Related
Go easy. I just started learning Flutter a week ago. I'm coming from ReactJS so I have a decent understanding of state management and lifecycle methods. But I'm completely new to Dart and Flutter and how it handles state.
I am writing a quick WebRTC chat application. I have a TextField I'm using to generate room names. I decided I wanted to make the labelText of the TextField, cycle through some random words, every 5 seconds, while the field is not in focus. If the field comes into focus, I stop cycling the label. I do this so that the field appears to have a pre generated random room name.
I am having trouble editing the TextField. I assume this is an issue with setState or my TextEditingController. I'm used to being able to access an input's value, so controllers are odd to me.
Here is my ChangingTextField:
import 'dart:async';
import 'package:english_words/english_words.dart';
import 'package:flutter/material.dart';
//
class ChangingTextField extends StatefulWidget {
final TextEditingController controller;
ChangingTextField({
Key? key,
required this.controller,
}) : super(key: key);
#override
_ChangingTextFieldState createState() => _ChangingTextFieldState();
}
class _ChangingTextFieldState extends State<ChangingTextField> {
FocusNode _focusNode = FocusNode();
Timer? _timer;
String _roomName = "example.com/";
bool _wasFocused = false;
#override
void initState() {
super.initState();
_focusNode = FocusNode();
_timer = Timer.periodic(Duration(seconds: 5), (Timer t) => _genRoomName());
}
#override
void dispose() {
_timer?.cancel();
_focusNode.dispose();
super.dispose();
}
void _requestFocus(){
if(!_wasFocused){
setState(() {
_timer?.cancel();
_wasFocused = true;
FocusScope.of(context).requestFocus(_focusNode);
});
}
}
void _genRoomName(){
WordPair wp = generateWordPairs().take(1).first;
setState(() => _roomName = "example.com/" + wp.first + "-" + wp.second );
}
#override
Widget build(BuildContext context) {
return Container(
child: TextField(
focusNode: _focusNode,
controller: widget.controller,
decoration: InputDecoration(
border: OutlineInputBorder(),
labelText: _wasFocused ? "example.com/" : _roomName,
),
onTap: _requestFocus,
),
);
}
}
The parent widget simply passes a TextEditingController into this widget so that I can listen for changes, and (I assume) gather the value of the TextField at a later point in time.
The listener is defined like this in the parent widget:
#override
void initState() {
roomNameController.addListener(() {
setState(() {});
});
super.initState();
}
However, every time I try to change the value of the TextField, after every character that I type, the focus is broken on the ChangingTextField widget, and I must click again inside the TextField to type my next character. I am assuming this issue is because the listener calls setState in the parent widget.
In React terminology I would refer to this as a re-render. If the parent re-renders, the child goes with it, and so the app loses what knowledge it had of where in the widget tree the user was working. However, I feel that the controller needs to exist in the parent, such that, I can acquire the value of the child when needed (e.g. on a button press). Lifting state up and whatnot.
Can someone explain to me what is going on here?
I found the solution. Listening inside of the widget instead of initializing the listener in the parent component, produces the behavior you would expect.
In short, moving the following code:
#override
void initState() {
roomNameController.addListener(() {
setState(() {});
});
super.initState();
}
into the ChangingTextField widget's initState as opposed to having it in the parent's initState, resolved the problem. Best of all, the controller is still created by the parent, so the controller's text is available in the parent when the submit button is pressed.
My screen has multiple textfields, about 15 or so. I don't want to use TextEditingController due to performance reasons as the number of TextFields are likely to grow and I need to pass data from one widget to another back and forth. So I am using OnChanged method of the TextField and am setting a variable which will be used from the parent widget through a function. Now when I click on reset on the parent widget, how do I clear all the values in the TextField controls without using TextEditingController?
class Parent extends StatelessWidget {
String txt='';
myfunction(text)
{
txt=text;
}
#override
Widget build(BuildContext context) {
...
Foo(myfunction);
....
}
}
class Foo extends StatelessWidget {
final Function myfunction;
const Foo(this.myfunction);
#override
Widget build(BuildContext context) {
return TextField(
onChanged: (text) {
myfunction( text);
},...
}
}
You should try to declare all textfields with:
final TextEditingController name = TextEditingController();
final TextEditingController age = TextEditingController();
Create one method like this :
resetAll() {
name.clear();
name.clear();
}
then you call resetAll on reset button like below:
onPressed:() => resetAll()
It's not possible, but the text Fields will be reset if you dispose and reopen the screen holding the text Fields.
How am I able to get the updated value of the TextFormField without using setState((){})?
On TextFormField 's onChanged method, I am setting the class variable to the value, but normally we would need setState((){}) for the value to be updated. I am just wondering how is this working?
class ResetPasswordPage extends StatefulWidget {
const ResetPasswordPage({ Key? key }) : super(key: key);
#override
_ResetPasswordPageState createState() => _ResetPasswordPageState();
}
class _ResetPasswordPageState extends State<ResetPasswordPage> {
String _currentPassword = '';
void onChanged(){
print('current Password is: ');
print(_currentPassword); ----------->this is printing the updated value, without setstate?
}
#override
Widget build(BuildContext context) {
return Container(
TextFormField(
onChanged: (val) => {
_currentPassword = val,
onChanged()
},
),
)
}
}
The variable value does change without the need to use setState, setState is only needed to tell Flutter that the UI has to change to reflect changes in your data.
From Flutter docs:
Calling setState notifies the framework that the internal state of this object has changed in a way that might impact the user interface in this subtree, which causes the framework to schedule a build for this State object.
You can create Notifier -> listener, then set the listener to listen for the Notifier,so any update on the Notifier(controller)it will notify the listener(TextFormField) to update itself.
Like this:
final _controller = TextEditingController();
child: TextFormField(
controller: _controller,
decoration: //decoration,
),
when you call this _controller.text it will notify all the listeners of this TextEditingController that needs update, then you get the same result setState((){}) will give you.
I implemented a custom DropdownButton widget, but I don't know how to implement it's setState. I would like to pass items and selectedItem to the widget, and let it to handle it's own state. And retrieve selected item when needed by myDropdownButton.selectedItem. How I could implement it?
class MyDropdownButton extends StatefulWidget {
final String selected;
final List<MyDropdownItem> items;
MyDropdownButton({Key key, this.selected, this.items})
: super(key: key);
#override
_MyDropdownButtonState createState() => _MyDropdownButtonState();
}
class _MyDropdownButtonState extends State<MyDropdownButton> {
Widget build(BuildContext context) {
return DropdownButtonFormField(
value: widget.selected,
onChanged: (String value) {
widget.selected = value;
},
But the selected is final and cannot be modified. How to implement it?
Thank you!
There are two questions here:
Updating the widget, using setState.
Passing the value back to the widget that is using the Dropdown with a callback. Medium Article on callbacks
Firstly to have the dropdown update, you need to call a setstate on the value change. But first, you'll need to receive the value passed, usually this is done in initstate.
Second, you need to use a callback function. The class that calls this widget/class can then receive and process that value
class MyDropdownButton extends StatefulWidget {
final String selected;
final List<MyDropdownItem> items;
final Function(String) valueReturned; //callback function
MyDropdownButton({Key key, this.selected, this.items, this.valueReturned})
: super(key: key);
#override
_MyDropdownButtonState createState() => _MyDropdownButtonState();
}
class _MyDropdownButtonState extends State<MyDropdownButton> {
String sel;
#override
void initState() {
super.initState();
sel = widget.selected; //get the value passed
}
Widget build(BuildContext context) {
return DropdownButtonFormField(
value: sel
onChanged: (String value) {
setState() {
sel = value;
widget.valueReturned(value); //this will trigger the callback function
},
}
In the code that calls the widget, you will need to listen to and handle the response.
Container(
child: MyDropdownButton(items: items, selected: selected, valueReturned: _handleValueReturned))
_handleValueReturned(String value) {
thingToUpdate = value;
}
Define a local variable and initialize it in initState():
String _selected;
#override
void initState() {
super.initState();
_selected = widget.selected;
}
use setState to update your local variable as the selection changes:
onChanged: (String value) {
setState(() {_selected = value;})
}
To retrieve the value, define a getter in your class:
String get selectedItem => _selected;
You can then access the selected item using myDropdownButton.selectedItem.
For more detailed explanation on implicit and explicit getters/setters see How do getters and setters change properties in Dart?
I am using flutter and I want to set text (String value) in TextFormField dynamically, means set value over press of a button.
use TextEditingController. Then assign it to the TextFormField then make use of the controller to assign the new data from wherever you want. If you want initial data assign it some value in the initState() function also use it on a stateful widget.
_textEditingController.text = "1";
You can make use of a StatefulWidget to adjust the initialValue property of your TextFormField.
class TextFieldChanger extends StatefulWidget {
#override
_TextFieldChangerState createState() => _TextFieldChangerState();
}
class _TextFieldChangerState extends State<TextFieldChanger> {
String presetText;
void _onPressed() {
setState(() {
presetText = 'updated text';
});
}
#override
Widget build(BuildContext context) => Column(children: [
TextFormField(initialValue: presetText),
RawMaterialButton(onPressed: _onPressed),
]);
}
In setState, I am assigning a new value to presetText and build will be called (with the updated initialValue) because of setState.