error message nt going even if my textfield is not empty - flutter

Question

Before I reach to my alert demo.. I am stuck in the beginning..
In my alert dialog there is a textField in content,
I have set an error text if textfield is empty but even after typing this error text not disappearing..it remains there....what is my fault...
here is my code
import 'package:flutter/material.dart';
class HomeScreen extends StatefulWidget {
#override
State<HomeScreen> createState() => _HomeScreenState();
}
class _HomeScreenState extends State<HomeScreen> {
String name='';
TextEditingController? txtname;
get _errortext {
final str=txtname!.value.text;
if(str.isEmpty)
return 'Cant be emtpy';
else
return null;
}
#override
void initState() {
// TODO: implement initState
super.initState();
txtname=TextEditingController();
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(title: Text('Demo Page'),),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Text('My Name is '+name),
SizedBox(height: 20.0,),
ElevatedButton(onPressed: (){
openDialog();
}, child: Text("Get Name")),
],),),);}
void openDialog() {showDialog(
context: context,
builder: (context)=>AlertDialog(
title: Text('Enter Your name here'),
content: TextField(
controller: txtname,
onChanged: (value){
setState(() {});},
decoration: InputDecoration(
hintText: 'Enter Name',
errorText: _errortext,
),),
actions: [
TextButton(onPressed: (){
}, child: Text('Submit')),
],
));
}}

Answer 1

To update inside dialog, you need to use StatefulBuilder and use its setState.
void openDialog() {
showDialog(
context: context,
builder: (context) => StatefulBuilder(
builder: (context, setState) => AlertDialog(
title: Text('Enter Your name here'),
content: TextField(
controller: txtname,
onTap: () {
setState(() {});
},
onChanged: (value) {
setState(() {});
},
decoration: InputDecoration(
hintText: 'Enter Name',
errorText: _errortext,
),
),
actions: [
TextButton(
onPressed: () {},
child: const Text('Submit'),
),
],
),
));
}
You can also separate the content StatefulWidget which is not needed in cases like this.