Add custom validation in Flutter using Firebase - flutter

Question

I have made a login page using Flutter which asks for 'Application Number (which are just numbers)', 'Password' & 'DOB' as shown below.
I have already added validations to it like it shouldn't be empty & only numbers & atleast one capital etc. But I also want to add custom validation using Firebase to Application Number & Password where only certain Application Numbers and their corresponding passwords will be allowed to enter which are specified in the database.
I have already added Firebase to my Flutter app.
Here is the code of the login page:
import 'package:flutter/material.dart';
import 'package:intl/intl.dart';
import 'home.dart';
class WelcomeScreen extends StatefulWidget {
#override
_WelcomeScreenState createState() => _WelcomeScreenState();
}
class _WelcomeScreenState extends State<WelcomeScreen> {
DateTime date = DateTime(2005, 06, 13);
TextEditingController dateinput = TextEditingController();
final formKey = GlobalKey<FormState>(); //key for form
String name = "";
#override
void initState() {
dateinput.text = ""; //set the initial value of text field
super.initState();
}
#override
Widget build(BuildContext context) {
final double height = MediaQuery.of(context).size.height;
final GlobalKey<ScaffoldState> _scaffoldKey = GlobalKey<ScaffoldState>();
return Scaffold(
key: _scaffoldKey,
appBar: AppBar(
backgroundColor: Colors.transparent,
elevation: 0,
),
backgroundColor: Color(0xFFffffff),
body: Container(
padding: const EdgeInsets.only(left: 40, right: 40),
child: SingleChildScrollView(
child: Form(
key: formKey, //key for form
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
SizedBox(height: height * 0.04),
Text(
"LEARNERS",
style: TextStyle(fontSize: 30, color: Color(0xFF363f93)),
),
Text(
"LICENSE TEST",
style: TextStyle(fontSize: 30, color: Color(0xFF363f93)),
),
SizedBox(
height: height * 0.05,
),
TextFormField(
decoration:
InputDecoration(labelText: "Enter Application Number"),
validator: (value) {
if (value!.isEmpty ||
!RegExp(r'^[0-9]+$').hasMatch(value)) {
return "This cannot be empty / \nThis can only contain numbers";
} else {
return null;
}
},
),
SizedBox(
height: height * 0.05,
),
TextFormField(
decoration: InputDecoration(labelText: "Enter Password"),
validator: (value) {
if (value!.isEmpty ||
!RegExp(r'^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)[a-zA-Z\d]{8,}$')
.hasMatch(value)) {
return "Minimum eight characters, \nat least one uppercase letter, \none lowercase letter and one number";
} else {
return null;
}
},
),
SizedBox(
height: height * 0.05,
),
GestureDetector(
child: TextFormField(
style: TextStyle(color: Colors.white),
controller:
dateinput, //editing controller of this TextField
decoration: InputDecoration(
labelStyle: TextStyle(color: Colors.white),
icon: Icon(Icons.calendar_today),
iconColor: Colors.white, //icon of text field
labelText: "Enter Date Of Birth" //label text of field
),
readOnly: true,
validator: (value) {
if (value!.isEmpty) {
return "Please select the Date of Birth";
} else {
return null;
}
}, //set it true, so that user will not able to edit text
onTap: () async {
DateTime? pickedDate = await showDatePicker(
context: context,
initialDate: date,
firstDate: DateTime(
1900), //DateTime.now() - not to allow to choose before today.
lastDate: DateTime(2006, 06, 13));
if (pickedDate != null) {
print(
pickedDate); //pickedDate output format => 2021-03-10 00:00:00.000
String formattedDate =
DateFormat('dd-MM-yyyy').format(pickedDate);
print(
formattedDate); //formatted date output using intl package => 2021-03-16
//you can implement different kind of Date Format here according to your requirement
setState(() {
dateinput.text =
formattedDate; //set output date to TextField value.
});
} else {
print("Date is not selected");
}
},
),
),
SizedBox(
height: height * 0.08,
),
Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: [
CircleAvatar(
radius: 30,
backgroundColor: Color(0xff4c505b),
child: IconButton(
color: Colors.white,
onPressed: () {
if (formKey.currentState!.validate()) {
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => TestScreen()),
);
}
},
icon: Icon(
Icons.arrow_forward,
)),
)
],
)
],
),
),
),
));
}
}