How to validate formfield - flutter

Question

Am a newbie though. I followed a tutorial for my code below which is a register form. How can i validate each input field since it's just one widget which is reused for the entire input field.
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Code
import 'package:flutter/material.dart';
import 'package:flutterlogindesign/utils/color.dart';
import 'package:flutterlogindesign/widgets/btn_widget.dart';
import 'package:flutterlogindesign/widgets/herder_container.dart';
class RegPage extends StatefulWidget {
#override
_RegPageState createState() => _RegPageState();
}
class _RegPageState extends State<RegPage> {
#override
Widget build(BuildContext context) {
return Scaffold(
body: Container(
padding: EdgeInsets.only(bottom: 30),
child: Column(
children: <Widget>[
HeaderContainer("Register"),
Expanded(
flex: 1,
child: Container(
margin: EdgeInsets.only(left: 20, right: 20, top: 30),
child: Column(
mainAxisSize: MainAxisSize.max,
children: <Widget>[
_textInput(hint: "Fullname", icon: Icons.person),
_textInput(hint: "Email", icon: Icons.email),
_textInput(hint: "Phone Number", icon: Icons.call),
_textInput(hint: "Password", icon: Icons.vpn_key),
Expanded(
child: Center(
child: ButtonWidget(
btnText: "REGISTER",
onClick: () {
Navigator.pop(context);
},
),
),
),
RichText(
text: TextSpan(children: [
TextSpan(
text: "Already a member ? ",
style: TextStyle(color: Colors.black)),
TextSpan(
text: "Login",
style: TextStyle(color: orangeColors)),
]),
)
],
),
),
)
],
),
),
);
}
Widget _textInput({controller, hint, icon}) {
return SingleChildScrollView(
child: Container(
margin: EdgeInsets.only(top: 10),
decoration: BoxDecoration(
borderRadius: BorderRadius.all(Radius.circular(20)),
color: Colors.white,
),
padding: EdgeInsets.only(left: 10),
child: TextFormField(
controller: controller,
decoration: InputDecoration(
border: InputBorder.none,
hintText: hint,
prefixIcon: Icon(icon),
),
),
),
);
}
}

Answer 1

Use Form Widget like the following
final _formKey = GlobalKey<FormState>();
bool autoValidate = false;
String phone;
child:Form( key: _formKey,
autovalidateMode: autoValidate ? AutovalidateMode.always : AutovalidateMode.disabled,
child: Column(
children: [
AppTextFormField(
initialValue: phone,
onChanged: (value) {
phone = value;
},
validator: (value) {
if (value.isEmpty) {
return 'Enter Phone number';
}
},
),
PrimaryButton(
text: 'Go',
onTap: () {
if (_formKey.currentState.validate()) {
_formKey.currentState.save();
} else {
autoValidate = true;
}
},
),
],
),
),