Flutter form validation not working when checking phone number entered - flutter

Question

I am trying to get form validation working, however, every time the form validates to true and I cannot work out why. Below is my code and every time I click "Save" the form validation passes even when the text box is empty.
There is a single validator for testing purposes checking if the contents of the text box is empty.
Any help would be greatly appreciated.
import 'package:flutter/material.dart';
class SignInScreen extends StatefulWidget {
#override
_SignInScreenState createState() => _SignInScreenState();
}
class _SignInScreenState extends State<SignInScreen> {
final GlobalKey<FormState> _formKey = GlobalKey<FormState>();
// Form field state
String phoneNumber;
void validateAndSave() {
final FormState form = _formKey.currentState;
if (form.validate()) {
print('Form is valid');
} else {
print('Form is invalid');
}
}
#override
Widget build(BuildContext context) {
return Scaffold(
body: Container(
padding: EdgeInsets.symmetric(
horizontal: 20.0,
vertical: 10.0,
),
child: Form(
key: _formKey,
child: Column(
children: <Widget>[
SizedBox(height: 10.0),
TextFormField(
validator: (value) {
value.isEmpty ? 'Enter a mobile phone number' : null;
},
keyboardType: TextInputType.phone,
decoration: InputDecoration(
contentPadding: EdgeInsets.symmetric(vertical: 15.0),
fillColor: Colors.white,
filled: true,
hintText: 'Mobile phone number',
prefixIcon: Icon(
Icons.phone_iphone,
size: 30.0,
),
),
onChanged: (value) {
setState(() => phoneNumber = value);
}),
SizedBox(height: 40.0),
FlatButton(
onPressed: () {
validateAndSave();
},
child: Text('Save'),
),
],
),
),
),
);
}
}

Answer 1

Solution is simple just add return keyword in the validator function.
import 'package:flutter/material.dart';
class SignInScreen extends StatefulWidget {
#override
_SignInScreenState createState() => _SignInScreenState();
}
class _SignInScreenState extends State<SignInScreen> {
final GlobalKey<FormState> _formKey = GlobalKey<FormState>();
// Form field state
String phoneNumber;
void validateAndSave() {
final FormState form = _formKey.currentState;
if (form.validate()) {
print('Form is valid');
} else {
print('Form is invalid');
}
}
#override
Widget build(BuildContext context) {
return Scaffold(
body: Container(
padding: EdgeInsets.symmetric(
horizontal: 20.0,
vertical: 10.0,
),
child: Form(
key: _formKey,
child: Column(
children: <Widget>[
SizedBox(height: 10.0),
TextFormField(
validator: (value) {
//Return a error string
return value.isEmpty ? 'Enter a mobile phone number' : null;
},
keyboardType: TextInputType.phone,
decoration: InputDecoration(
contentPadding: EdgeInsets.symmetric(vertical: 15.0),
fillColor: Colors.white,
filled: true,
hintText: 'Mobile phone number',
prefixIcon: Icon(
Icons.phone_iphone,
size: 30.0,
),
),
onChanged: (value) {
setState(() => phoneNumber = value);
}),
SizedBox(height: 40.0),
FlatButton(
onPressed: () {
validateAndSave();
},
child: Text('Save'),
),
],
),
),
),
);
}
}