Manually setting Flutter Validation Error - forms

Question

After validating a form and sending a request from flutter to the server backend: I want to set any potential error message from the server to be displayed in the original form. Preferably exactly like a validation error.
For instance:
Widget build(BuildContext context) {
...
TextFormField(
onFieldSubmitted: (value) => _signIn(),
validator: (input) {
if (input.length < 6)
return 'Your password is too short';
return null;
},
onSaved: (input) => _password = input,
decoration: InputDecoration(
labelText: 'Password',
),
obscureText: true,
)
...
}
Future<void> _signIn() async {
final formState = _formKey.currentState;
if (!formState.validate()) return;
formState.save();
try {
... // do fancy request stuff
} catch (e) {
// this is where I want to set the "validation" error
}
}

Answer 1

It's actually super simple and the validation error still works aswell.
String? _errorMsg;
Widget build(BuildContext context) {
...
TextFormField(
onFieldSubmitted: (value) => _signIn(),
validator: (input) {
if (input.length < 6)
// will set the errorText directly, no need for a variable here
return 'Your password is too short';
return null;
},
onSaved: (input) => _password = input,
decoration: InputDecoration(
labelText: 'Password',
errorText: _errorMsg,
),
obscureText: true,
)
...
}
Future<void> _signIn() async {
setState(() {
_errorMsg = null; // clear any existing errors
});
final formState = _formKey.currentState;
if (!formState.validate()) return;
formState.save();
try {
... // do fancy request stuff
} catch (e) {
setState(() {
_errorMsg = 'Wrong password.';
});
}
}

Answer 2

I suppose, I could think of a solution, but I think it's kind of ugly.
I could have an "error" variable, that is set when the request fails.
I would then call formState.validate() a second time, in there: check the error variable and return it if it's not null.

Answer 3

You can use flutter_form_bloc and use addError method of TextFieldBloc.
usernameField.addError('That username is taken. Try another.');
Keep in mind that you can also use asynchronous validators.
This is a complete example:
dependencies:
flutter:
sdk: flutter
flutter_bloc: ^0.21.0
form_bloc: ^0.5.0
flutter_form_bloc: ^0.4.1+1
import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:flutter_form_bloc/flutter_form_bloc.dart';
import 'package:form_bloc/form_bloc.dart';
void main() {
runApp(MaterialApp(home: SignUpForm()));
}
class SignUpFormBloc extends FormBloc<String, String> {
final usernameField = TextFieldBloc();
final passwordField =
TextFieldBloc(validators: [Validators.passwordMin6Chars]);
#override
List<FieldBloc> get fieldBlocs => [usernameField, passwordField];
#override
Stream<FormBlocState<String, String>> onSubmitting() async* {
// Form logic...
try {
await _signUp(
throwException: true,
username: usernameField.value,
password: passwordField.value,
);
yield currentState.toSuccess();
} catch (e) {
// When get the error from the backend you can
// add the error to the field:
usernameField.addError('That username is taken. Try another.');
yield currentState
.toFailure('The error was added to the username field.');
}
}
Future<void> _signUp({
#required bool throwException,
#required String username,
#required String password,
}) async {
print(username);
print(password);
await Future<void>.delayed(Duration(seconds: 2));
if (throwException) throw Exception();
}
}
class SignUpForm extends StatelessWidget {
#override
Widget build(BuildContext context) {
return BlocProvider<SignUpFormBloc>(
builder: (context) => SignUpFormBloc(),
child: Builder(
builder: (context) {
final formBloc = BlocProvider.of<SignUpFormBloc>(context);
return Scaffold(
appBar: AppBar(title: Text('Sign Up Form')),
body: FormBlocListener<SignUpFormBloc, String, String>(
onSubmitting: (context, state) {
// Show the progress dialog
showDialog(
context: context,
barrierDismissible: false,
builder: (_) => WillPopScope(
onWillPop: () async => false,
child: Center(
child: Card(
child: Container(
width: 80,
height: 80,
padding: EdgeInsets.all(12.0),
child: CircularProgressIndicator(),
),
),
),
),
);
},
onSuccess: (context, state) {
// Hide the progress dialog
Navigator.of(context).pop();
// Navigate to success screen
Navigator.of(context).pushReplacement(
MaterialPageRoute(builder: (_) => SuccessScreen()));
},
onFailure: (context, state) {
// Hide the progress dialog
Navigator.of(context).pop();
// Show snackbar with the error
Scaffold.of(context).showSnackBar(
SnackBar(
content: Text(state.failureResponse),
backgroundColor: Colors.red[300],
),
);
},
child: ListView(
children: <Widget>[
TextFieldBlocBuilder(
textFieldBloc: formBloc.usernameField,
decoration: InputDecoration(labelText: 'Username'),
),
TextFieldBlocBuilder(
textFieldBloc: formBloc.passwordField,
decoration: InputDecoration(labelText: 'Password'),
),
Padding(
padding: const EdgeInsets.all(8.0),
child: RaisedButton(
onPressed: formBloc.submit,
child: Center(child: Text('SUBMIT')),
),
),
],
),
),
);
},
),
);
}
}
class SuccessScreen extends StatelessWidget {
const SuccessScreen({Key key}) : super(key: key);
#override
Widget build(BuildContext context) {
return Scaffold(
backgroundColor: Colors.green[300],
body: Center(
child: SingleChildScrollView(
child: Column(
children: <Widget>[
Icon(
Icons.sentiment_satisfied,
size: 100,
),
RaisedButton(
color: Colors.green[100],
child: Text('Sign out'),
onPressed: () => Navigator.of(context).pushReplacement(
MaterialPageRoute(builder: (_) => SignUpForm())),
)
],
),
),
),
);
}
}

Answer 4

A simple solution:
Make a key for the widgets state:
GlobalKey<_CustomErrorTextField> _passwordTextFieldState = GlobalKey();
Set the Error message using the key:
_passwordTextFieldState.currentState.updateError(errorMsg);
Reset the error after 2 seconds:
Future.delayed(Duration(seconds: 2), () {
// Runs after duration sec
_passwordTextFieldState.currentState.updateError(null);
});
Set up the widget (be sure to set the key):
CustomErrorTextField(
key: _passwordTextFieldState,
label: "Password",
currentPassword: password,
validator: yourValidator,
callback: passwordCallback,
obscureText: hidePassword.value - a bool value show/hide password
)
Here is the Widget:
class CustomErrorTextField extends StatefulWidget {
CustomErrorTextField({
Key key,
this.label,
this.currentPassword,
this.validator,
this.callback,
this.obscureText = false
}): super(key: key);
final String label;
final String currentPassword;
final FormFieldValidator<String> validator;
final Function callback;
final obscureText;
#override
_CustomErrorTextField createState() => _CustomErrorTextField();
}
class _CustomErrorTextField extends State<CustomErrorTextField> {
String errorMsg;
updateError(String errorMsg){
setState(() {
this.errorMsg = errorMsg;
});
}
#override
Widget build(BuildContext context) {
return TextFormField(
decoration: InputDecoration(
labelText: widget.label,
errorText: errorMsg
),
initialValue: widget.currentPassword,
keyboardType: TextInputType.visiblePassword,
validator: widget.validator,
onSaved: (String val) {
widget.callback(val);
},
obscureText: widget.obscureText,
);
}
}