how to get key from build Widget - dart

Question

I want to get value key which contains in Widget build(), but it says 'Undefined'. Also, I need to get this value to another class. How can I do it?
I`ve tried to just take this value, but it says undefined error
String newValue = s; // It says Undefined
I also tried to get this value to another class but this method gives more errors :c
myCard c = myCard();
String classValue = c.s; // It says 'Only static members can be accessed in initializers' and 'The getter 's' isn`t defined for the class 'myCard' '
Here`s part of main.dart file
class MyCard extends StatefulWidget {
#override
myCard createState() => myCard();
}
class myCard extends State<MyCard> {
int myCount = count - 1;
void click() {
setState(() {
print(titlecard);
Navigator.push(context, MaterialPageRoute(
builder: (context) => setNewText())
);
});
}
#override
Widget build(BuildContext context) {
Key s = Key(myCount.toString()); // I want to get this value
return Center(
key: s,
child: Card(
child: Column(
mainAxisSize: MainAxisSize.min,
children: <Widget>[
ListTile(
leading: Icon(Icons.album),
title: Text(titlecard[int.parse(s)]),
subtitle: Text(textcard),
),
ButtonTheme.bar( // make buttons use the appropriate styles for cards
child: ButtonBar(
children: <Widget>[
FlatButton(
child: const Text('Change Text'),
onPressed: click,
),
FlatButton(
child: const Text('LISTEN'),
onPressed: () {
print(s);
},
),
],
),
),
],
),
),
);
}
}
class setNewText extends StatefulWidget {
#override
SetNewText createState() => SetNewText();
}
class SetNewText extends State<setNewText> {
myCard c = myCard();
HomePageState s = HomePageState();
String v = c.s; // To here
final titleController = TextEditingController();
final textController = TextEditingController();
final formkey = GlobalKey<FormState>();
List<String> titles = [''];
void _submit() {
setState(() {
if (formkey.currentState.validate()) {
formkey.currentState.save();
Navigator.pop(context);
titlecard.removeAt(count-s.myCount);
titlecard.insert(count-s.myCount, titleController.text);
textcard = textController.text;
}
});
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('Change Title'),
),
body: Column(
children: <Widget>[
Card(
child: Padding(
padding: EdgeInsets.all(2.0),
child: Form(
key: formkey,
child: Column(
children: <Widget>[
TextFormField(
controller: titleController,
decoration: InputDecoration(
labelText: 'Title'
),
validator: (value) => value.length < 1 ? 'Invalid Title' : null,
onSaved: (value) => value = titleController.text,
),
TextFormField(
controller: textController,
decoration: InputDecoration(
labelText: 'Text'
),
validator: (text) => text.length < 1 ? 'Invalid Text' : null,
onSaved: (text) => text = textController.text,
)
],
),
),
),
),
FlatButton(
textColor: Colors.deepPurple,
child: Text('SUBMIT'),
onPressed: _submit,
),
],
)
);
}
}

Answer 1

Since you're just listening for values, one way of doing this is by listening to the value using Streams. You can initialize the class where the value can be Streamed and access it anywhere. Do note that once the Stream has been closed, you can only create a new Stream.
Here's a sample.
import 'dart:async';
import 'package:flutter/material.dart';
class SampleStream extends StatefulWidget {
const SampleStream({Key? key, required this.title}) : super(key: key);
final String title;
#override
State<SampleStream> createState() => _MyHomePageState();
}
class _MyHomePageState extends State<SampleStream> {
Counter counter = Counter();
#override
Widget build(BuildContext context) {
return StreamBuilder<int>(
stream: counter.showCount,
builder: (context, AsyncSnapshot<int> snapshot) {
int count = snapshot.hasData ? snapshot.data! : 0;
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: Text(
'You clicked the button $count times'),
),
floatingActionButton: FloatingActionButton(
child: const Icon(Icons.plus_one),
onPressed: () {
counter.setCount(++count);
},
),
);
});
}
#override
void dispose() {
super.dispose();
counter.disposeCount();
}
}
class Counter {
final _count = StreamController<int>.broadcast();
Stream<int> get showCount => _count.stream;
setCount(int count) {
debugPrint('Stream sink: $count');
_count.sink.add(count);
}
disposeCount() {
_count.close();
}
}
In this demo, Counter was initialized in _MyHomePageState and can only be accessed in the same class. Calling counter.setCount(int) updates the stream and the stream value can be listened to using StreamBuilder to fetch the snapshot.