Form Validation in Flutter

Last Updated : 11 Apr, 2025

Form Validation is an important part of every application. In the flutter application, there are many ways to validate form such as using a TextEditingController. But handling text controller for every Input can be messy in big applications. Hence, Form provides us a convenient way to validate user Inputs.

In form, the input is validated in your submit function(the function which is called once the user has entered every detail, But the condition is applied in each TextFormField itself with a widget name validator as shown in the below given example.

The Validator widget takes a function with a parameter that contains the value of the single input and then it checks the condition which is given in the validator function. The key is used in this because there can be many inputs so to connect the widget tree with elementary tree key of type FormState is used.

In the Code below, if the input validation in the form fails, it will lead to the following:

Steps to implement Form in Flutter

Step 1: Initialize global key

Initialize the global key to a variable like _formKey here, because with this variable we can validate and save the Initializeform.

Dart

var _formKey = GlobalKey<FormState>();

Step 2: Wrap with Form widget

Wrap the whole form with the Form widget and give the global key as the key, because it creates a container for form fields.

Dart

Form(     	key: _formKey,     	child: Column(     		children: <Widget>[     	            //Code for whole form     	       ]     	   ),     )

Step 3: Validate and Save

_formKey.currentState!.validate(): Validates every FormField that is a descendant of this Form, and returns true if there are no errors.
_formKey.currentState!.save(): Saves every FormField that is a descendant of this Form.

Dart

// Validate the form fields final isValid = _formKey.currentState!.validate(); if (!isValid) { 	// If the form is not valid, return without doing anything 	return; } else { 	// If the form is valid, show a success message 	ScaffoldMessenger.of(context).showSnackBar( 		SnackBar( 			backgroundColor: Colors.green, 			content: Text( 				"Successfully logged in", 				style: TextStyle( 					color: Colors.white, 				), 			), 		), 	); } // Save the form state _formKey.currentState!.save();

Complete source code

main.dart:

Dart

import 'package:flutter/material.dart';  void main() => runApp(MyApp());  class MyApp extends StatelessWidget { 	@override 	Widget build(BuildContext context) { 		return MaterialApp( 			home: HomePage(), 			debugShowCheckedModeBanner: false, 		); 	} }  class HomePage extends StatefulWidget { 	@override 	_HomePageState createState() => _HomePageState(); }  class _HomePageState extends State<HomePage> { 	var _formKey = GlobalKey<FormState>();  	// Function to handle form submission 	void _submit() { 		// Validate the form fields 		final isValid = _formKey.currentState!.validate(); 		if (!isValid) { 			// If the form is not valid, return without doing anything 			return; 		} else { 			// If the form is valid, show a success message 			ScaffoldMessenger.of(context).showSnackBar( 				SnackBar( 					backgroundColor: Colors.green, 					content: Text( 						"Successfully logged in", 						style: TextStyle( 							color: Colors.white, 						), 					), 				), 			); 		} 		// Save the form state 		_formKey.currentState!.save(); 	}  	@override 	Widget build(BuildContext context) { 		return Scaffold( 			appBar: AppBar( 				title: Text("Form Validation"), 				leading: Icon(Icons.filter_vintage), 			), 			body: Padding( 				padding: const EdgeInsets.all(16.0), 				child: Form( 					key: _formKey, 					child: Column( 						children: <Widget>[ 							Text( 								"Form-Validation In Flutter", 								style: TextStyle(fontSize: 24.0, fontWeight: FontWeight.bold), 							), 							SizedBox( 								height: MediaQuery.of(context).size.width * 0.1, 							), 							TextFormField( 								decoration: InputDecoration(labelText: 'E-Mail'), 								keyboardType: TextInputType.emailAddress, 								validator: (value) { 									if (value!.isEmpty || 											!RegExp(r"^[a-zA-Z0-9.a-zA-Z0-9.!#$%&'*+-/=?^_`{|}~]+@[a-zA-Z0-9]+\.[a-zA-Z]+") 													.hasMatch(value)) { 										return 'Enter a valid email!'; 									} 									return null; 								}, 							), 							SizedBox( 								height: MediaQuery.of(context).size.width * 0.1, 							), 							TextFormField( 								decoration: InputDecoration(labelText: 'Password'), 								obscureText: true, 								validator: (value) { 									if (value!.isEmpty) { 										return 'Enter a valid password!'; 									} 									return null; 								}, 							), 							SizedBox( 								height: MediaQuery.of(context).size.width * 0.1, 							), 							SizedBox( 								width: double.infinity, // Set the width to fill the parent 								child: ElevatedButton( 									style: ButtonStyle( 										backgroundColor: WidgetStateProperty.all(Colors.green), 									), 									child: Padding( 										padding: const EdgeInsets.all(8.0), 										child: Text( 											"Submit", 											style: TextStyle( 												color: Colors.white, 												fontSize: 20, 											), 										), 									), 									onPressed: () => _submit(), 								), 							), 						], 					), 				), 			), 		); 	} }

Output:

Designing a Form Submission Page in Flutter

AkashDubey3

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Form Validation in Flutter

Steps to implement Form in Flutter

Step 1: Initialize global key

Step 2: Wrap with Form widget

Step 3: Validate and Save

Complete source code

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