Showing TextField's error text does not work - flutter

Question

I'm building the changePassword module on an app and I want to check that the field its not empty but its not working and I don't know why
Card(
color: Color(0xFFDBE2EF),
margin: EdgeInsets.symmetric(
vertical: 10, horizontal: 25),
child: TextField(
controller: passwordConfirmController,
obscureText: true,
decoration: InputDecoration(
border: OutlineInputBorder(),
labelText: 'Confirmar contraseña',
labelStyle:
TextStyle(fontFamily: 'Montserrat')),
),
),
SizedBox(
height: 20,
),
RaisedButton(
color: Color(0xFFDBE2EF),
onPressed: () => {
setState(() {
print("Valor _validate antes");
print(_validate);
print("Valor isEmpty");
print(passwordController.text.isEmpty);
passwordController.text.isEmpty
? _validate = true
: _validate = false;
_isLoading = true;
print("Valor _validate después");
print(_validate);
}),
changePass(passwordController.text),
},
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.circular(5),
),
child: Text(
'Actualizar',
style: TextStyle(
fontSize: 20,
fontFamily: 'Montserrat',
color: Color(0xFF002D53),
fontWeight: FontWeight.bold),
)),
The values on raisedbutton where I check if the password is empty seems to be working printing the expected values, but the error text does not work

Answer 1

You need to pass the error text to the TextField
TextField(
decoration: InputDecoration(
errorText:"some error",
),

Answer 2

You have to change _validate property inside setState(), and based on that change TextField error text
class FirstScreen extends StatefulWidget {
#override
_FirstScreenState createState() => _FirstScreenState();
}
class _FirstScreenState extends State<FirstScreen> {
final passwordConfirmController = TextEditingController();
bool _validate = false;
void _validatePassword() {
if (passwordConfirmController.text.isEmpty) {
_validate = true;
} else {
_validate = false;
}
setState(() {
_validate;
print("Valor _validate después");
print(_validate);
});
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(),
body: Column(
children: <Widget>[
Card(
color: Color(0xFFDBE2EF),
margin: EdgeInsets.symmetric(vertical: 10, horizontal: 25),
child: TextField(
controller: passwordConfirmController,
obscureText: true,
decoration: InputDecoration(
errorText: _validate ? "Enter Password" : null,
border: OutlineInputBorder(),
labelText: 'Confirmar contraseña',
labelStyle: TextStyle(fontFamily: 'Montserrat')),
),
),
SizedBox(
height: 20,
),
RaisedButton(
color: Color(0xFFDBE2EF),
onPressed: () => {_validatePassword()},
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.circular(5),
),
child: Text(
'Actualizar',
style: TextStyle(
fontSize: 20,
fontFamily: 'Montserrat',
color: Color(0xFF002D53),
fontWeight: FontWeight.bold),
)),
],
),
);
}
}