onChanged method with setState of TextField does not update the result? - flutter

Question

I am experimenting with flutter and I have a very simple code as follows:
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
class Test extends StatefulWidget {
#override
_TestState createState() => _TestState();
}
class _TestState extends State<Test> {
static double d = 0;
static TextEditingController editingController = TextEditingController();
#override
void initState() {
editingController.addListener(() {
setState(() {});
});
super.initState();
}
#override
void dispose() {
editingController.dispose();
super.dispose();
}
Calc calc = Calc(d: d, e: editingController);
#override
Widget build(BuildContext context) {
return Scaffold(
body: Center(
child: Padding(
padding: const EdgeInsets.all(25),
child: Column(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: [
TextField(
keyboardType: TextInputType.number,
onChanged: (value) {
setState(() {
if (value.isNotEmpty) {
d = double.parse(value);
} else if (value.isEmpty) {
d = 0;
}
});
},
inputFormatters: [
FilteringTextInputFormatter.allow(
RegExp(r'(^(\d{1,})\.?(\d{0,2}))'),
),
],
),
TextField(
keyboardType: TextInputType.number,
controller: editingController,
inputFormatters: [
FilteringTextInputFormatter.allow(
RegExp(r'(^(\d{1,})\.?(\d{0,2}))'),
),
],
),
Text(
'First Text Field Value + 2 = \n${calc.dString()}',
style: TextStyle(fontSize: 30, color: Colors.purpleAccent),
),
Text(
calc.eString(),
style: TextStyle(fontSize: 30, color: Colors.deepOrangeAccent),
),
],
),
),
),
);
}
}
class Calc {
final double d;
final TextEditingController e;
Calc({this.d, this.e});
String dString() {
double result = d + 2;
return result.toStringAsFixed(0);
}
String eString() {
return e.text;
}
}
As we can see I am passing both the text fields' values into another class for some math and getting the results. These results are displayed using the Text widgets.
For the 1st TextField, I have used onChange method, and for the 2nd TextField, I have used TextEditingController.
I get return value for 2nd TextField from the Calc class, but not for the 1st TextField!
I think I am missing something basic and I did not find any solution so far. Can you please help me what am I missing here.

Answer 1

1st of all, you are creating just a single object of Calc,
yes as you can see your 2nd textField update perfectly because it's using TextEditingController but for the 1st one, it just call once and become 2 because of dString(), while on 1st run d becomes 0 passed on Calc.
if you want to use Calc to update text, you can simply put it inside build method like this , i dont suggest it, you can use callBackMethod to handle this or use another TextEditingController.
Hope you get it now
#override
Widget build(BuildContext context) {
Calc calc = Calc(d: d, e: editingController);
return Scaffold(
body: Center(

Answer 2

Your Calc Object is not being affect by setState() call. To run be able to get value of the calcobject, run it in you onChanged() function.