How to handle TextField validation in password in Flutter

Your regular expression should look like:

r'^(?=.*?[A-Z])(?=.*?[a-z])(?=.*?[0-9])(?=.*?[!@#\$&*~]).{8,}$ 

Here is an explanation:

r'^ (?=.*[A-Z]) // should contain at least one upper case (?=.*[a-z]) // should contain at least one lower case (?=.*?[0-9]) // should contain at least one digit (?=.*?[!@#\$&*~]) // should contain at least one Special character .{8,} // Must be at least 8 characters in length $ 

Match above expression with your password string. Using this method-

 String? validatePassword(String value) { RegExp regex = RegExp(r'^(?=.*?[A-Z])(?=.*?[a-z])(?=.*?[0-9])(?=.*?[!@#\$&*~]).{8,}$'); if (value.isEmpty) { return 'Please enter password'; } else { if (!regex.hasMatch(value)) { return 'Enter valid password'; } else { return null; } } } 

You can achieve this using below flutter plugin.

wc_form_validators

You can use it something like this:

 TextFormField( decoration: InputDecoration( labelText: 'Password', ), validator: Validators.compose([ Validators.required('Password is required'), Validators.patternString(r'^(?=.*?[A-Z])(?=.*?[a-z])(?=.*?[0-9])(?=.*?[!@#\$&*~]).{8,}$', 'Invalid Password') ]), ), 

Its documentation is really good. You can read it for more util functions like this.

You have to use TextFormField widget with validator property.

TextFormField( validator: (value) { // add your custom validation here. if (value.isEmpty) { return 'Please enter some text'; } if (value.length < 3) { return 'Must be more than 2 charater'; } }, ), 

Take a look on official docs: https://flutter.dev/docs/cookbook/forms/validation

By using extension in dart

extension PasswordValidator on String { bool isValidPassword() { return RegExp( r'^(?=.*?[A-Z])(?=.*?[a-z])(?=.*?[0-9])(?=.*?[!@#\$&*~]).{8,}$') .hasMatch(this); } } 

You can apply this in your textfield like

TextFormField( autovalidate: true, validator: (input) => input. isValidPassword() ? null : "Check your password...", ) 

Flutter Login Validation

 ///creating Username and Password Controller. TextEditingController username=TextEditingController(); TextEditingController password=TextEditingController(); Form( child: Builder( builder: (context) { return Column( children: [ TextFormField( controller: username, validator: (CurrentValue){ var nonNullValue=CurrentValue??''; if(nonNullValue.isEmpty){ return ("username is required"); } if(!nonNullValue.contains("@")){ return ("username should contains @"); } return null; }, ), TextFormField( controller: password, validator: (PassCurrentValue){ RegExp regex=RegExp(r'^(?=.*?[A-Z])(?=.*?[a-z])(?=.*?[0-9])(?=.*?[!@#\$&*~]).{8,}$'); var passNonNullValue=PassCurrentValue??""; if(passNonNullValue.isEmpty){ return ("Password is required"); } else if(passNonNullValue.length<6){ return ("Password Must be more than 5 characters"); } else if(!regex.hasMatch(passNonNullValue)){ return ("Password should contain upper,lower,digit and Special character "); } return null; }, ), ElevatedButton(onPressed: (){ if(Form.of(context)?.validate()?? false){ Navigator.of(context).push(MaterialPageRoute(builder: (_)=>loginpage())); } }, child: Text("Login")) ], ); } ), ) 

in this picture you can see when you Enter inValid username and password it will not Navigate to another page.

when you Enter Valid Username and Password it will Navigate to another Page.

 import 'package:firebase_auth/firebase_auth.dart'; import 'package:flutter/material.dart'; import 'package:flutter_pw_validator/flutter_pw_validator.dart'; import 'Card_Creation.dart'; class SignUp extends StatefulWidget { const SignUp({Key? key}) : super(key: key); @override State<SignUp> createState() => _SignUpState(); } class _SignUpState extends State<SignUp> { TextEditingController _useremail = TextEditingController(); TextEditingController _userpass = TextEditingController(); final _formKey = GlobalKey<FormState>(); @override void dispose() { _useremail.dispose(); _userpass.dispose(); super.dispose(); } @override Widget build(BuildContext context) { return Scaffold( body: Padding( padding: const EdgeInsets.all(20.0), child: SizedBox( width: MediaQuery.of(context).size.width, height: MediaQuery.of(context).size.height, child: Center( child: Form( key: _formKey, child: SingleChildScrollView( child: Column( crossAxisAlignment: CrossAxisAlignment.start, mainAxisAlignment: MainAxisAlignment.center, children: [ const Text( 'Sign Up here....!', style: TextStyle( color: Colors.black, fontWeight: FontWeight.bold, fontSize: 25), ), const SizedBox( height: 10, ), TextFormField( validator: (value) { var availableValue = value ?? ''; if (availableValue.isEmpty) { return ("Username is required"); } if (!availableValue.contains("@") || !availableValue.endsWith("gmail.com")) { return ("Username should be a valid Gmail address"); } return null; }, controller: _useremail, keyboardType: TextInputType.emailAddress, obscureText: false, decoration: InputDecoration( hintText: 'Your email address', enabledBorder: OutlineInputBorder( borderRadius: BorderRadius.circular(20), borderSide: const BorderSide(color: Colors.blueGrey)), focusedBorder: OutlineInputBorder( borderRadius: BorderRadius.circular(20), borderSide: const BorderSide(color: Colors.greenAccent), ), ), ), const SizedBox( height: 10, ), TextFormField( validator: (value) { if (value == null || value.isEmpty) { return "Password is required"; } // Perform custom password validation here if (value.length < 8) { return "Password must be at least 8 characters long"; } if (!value.contains(RegExp(r'[A-Z]'))) { return "Password must contain at least one uppercase letter"; } if (!value.contains(RegExp(r'[a-z]'))) { return "Password must contain at least one lowercase letter"; } if (!value.contains(RegExp(r'[0-9]'))) { return "Password must contain at least one numeric character"; } if (!value.contains(RegExp(r'[!@#\$%^&*()<>?/|}{~:]'))) { return "Password must contain at least one special character"; } return null; // Password is valid. }, controller: _userpass, keyboardType: TextInputType.visiblePassword, obscureText: true, decoration: InputDecoration( hintText: 'Enter Your password', enabledBorder: OutlineInputBorder( borderRadius: BorderRadius.circular(20), borderSide: const BorderSide(color: Colors.blueGrey)), focusedBorder: OutlineInputBorder( borderRadius: BorderRadius.circular(20), borderSide: const BorderSide(color: Colors.greenAccent), ), ), ), const SizedBox( height: 10, ), FlutterPwValidator( controller: _userpass, minLength: 8, uppercaseCharCount: 1, lowercaseCharCount: 1, numericCharCount: 1, specialCharCount: 1, width: 200, height: 150, onSuccess: () { return null; // Password is valid. }, ), const SizedBox( height: 10, ), Align( alignment: Alignment.center, child: ElevatedButton( onPressed: () { if (_formKey.currentState!.validate()) { ScaffoldMessenger.of(context).showSnackBar( const SnackBar(content: Text('Processing Data')), ); _signup(); } }, child: const Text('Register'), ), ), const SizedBox( height: 10, ), ], ), ), ), ), ), ), ); } void _routing_with_clearfields() { _useremail.clear(); _userpass.clear(); _snackonsignup(); // Navigate to the next screen using Navigator. Navigator.of(context).pushReplacement( MaterialPageRoute(builder: (context) => MyCard()), ); } void _signup() async { try { await FirebaseAuth.instance.createUserWithEmailAndPassword( email: _useremail.text.trim(), password: _userpass.text); _routing_with_clearfields(); } on FirebaseAuthException catch (e) { if (e.code == 'weak-password') { print('The password provided is too weak.'); } else if (e.code == 'email-already-in-use') { print('The account already exists for that email.'); } } catch (e) { print(e); } } void _snackonsignup() { final snack = SnackBar( content: const Text( 'SignUp successfully', style: TextStyle(color: Colors.black, fontSize: 15), ), backgroundColor: Colors.lightGreen.shade300, ); ScaffoldMessenger.of(context).showSnackBar(snack); } } Use this code it validates with using flutter package: flutter_pw_validator: ^1.6.0 

here is the complete answer

Write a Dart program to check whether a string is a valid password. a. A password must have at least ten characters. b. A password consists of only letters and digits. c. A password must contain at least two digits.

import 'dart:io'; main() { var password; stdout.write("Enter You'r Password: "); password=stdin.readLineSync(); if(password.length>=10 && !password.contains(RegExp(r'\W')) && RegExp(r'\d+\w*\d+').hasMatch(password)) { print(" \n\t$password is Valid Password"); } else { print("\n\t$password is Invalid Password"); } 

validator: (value) { password = value; var passwordvalid = RegExp( r'^(?=.*?[A-Z])(?=.*?[a-z])(?=.*?[0-9])(?=.*?[!@#\$&*~]).{8,}$').hasMatch(value!); if (value.isEmpty) { return "Enter Password"; } if (!passwordvalid) { return "Your Password is In-Valid"; } }, 

this is the best regx bool passValid = RegExp("^(?=.{8,32}\$)(?=.*[A-Z])(?=.*[a-z])(?=.*[0-9])(?=.*[!@#\$%^&*(),.?:{}|<>]).*").hasMatch(value); if (value.isEmpty ||!passValid) { return 'error'; }