Validating user input plays an important role in developing any app. This process helps improve the app’s security. It checks the correctness of the information provided by the user so as not to introduce bugs into the application.
Form validation is the process of ensuring that user input meets the requirements of the Form. This process includes verifying that the input is of the correct type (e.g. number, email address, etc.), that the input is in the correct format (e.g. correctly spelt, all lowercase, etc.), and that the input is within the allowable range. Get support by hiring Flutter developer from a trusted US based local companies like Flutter Agency and Bosc Tech Labs.
This article aims to show you how to create form validation in Flutter in an efficient manner. You’ll be able to use the concepts from this blog post in all of your future app development projects once you’ve finished reading it.
Why is Form Validation Important?
Form validation in Flutter is important because it protects your application from bad data. Invalid input can cause your application to crash, behave unpredictably, or even leak sensitive data. By validating user input, you can prevent these issues from arising.
How Does Form Validation Work in Flutter?
Form validation in the Flutter app is based on the Validator widget. A Validator widget is a simple, stateless widget that takes a single input and validates it according to a given set of rules. The Form widget uses the Validator widget to validate user input.
For example, when a user enters data into a form, the Form widget passes that data to a Validator widget for validation. The Validator widget passes the data onto the Form widget if the data is valid. If the data is invalid, the Validator widget sets an error message, and the Form widget displays it to the user.
In this example, we will learn how to validate a form that has a single text field using the following steps:
- Create a sign-up page
- Create a form using the global key
- Form validation using TextFormField widget
- Validation button to submit the Form
Create a sign-up page
The first step is to create a login page which asks the user to enter the details like name, email, phone number and password. We want our app users to fill in the correct details in each field for validation.
Therefore, the logic will follow the definition is described as such:
First, we want the user to enter a valid first name and last name for the name field, which initials can accompany. For the email field, we want a valid email containing some characters before the “@” sign and the email domain at the end of the email.
For phone number validation, the user needs to enter a valid phone number having 11 digits starting with zero. Finally, for our password validation, we expect the user to use a combination of an uppercase letter, a lowercase letter, a digit, and a special character.
Only when the user’s input matches the above do we want to accept their input before making any requests, such as sending to a server or saving in a database.
Creating a form by global key
The Form widget is required to validate user input. The Form widget acts as a container for many TextFormFields to be validated, and it requires a GlobalKey to be uniquely identified. It’s also used to obtain the Form’s current state.
Form validation using TextFormField widget
The Form is in position, but there is no method for people to add text. A TextFormField’s job is to do just that. The TextFormField widget displays validation failures when they occur and generates a UI design text field.
The TextFormField’s job is to render the user’s UI interface and notify the validation error when the user inputs erroneous data. To validate the input, the TextFormField contains a validator method.
If the user input is invalid, the validator method provides a string with the error message; otherwise, it returns null. In most circumstances, a regular expression will check the input. For example, to validate the user’s email and password, we’ll utilise the InputValidationMixinmixin’sisEmailValid and isPasswordValid functions.
Validation button to submit the Form
After you’ve created a structure with an input field, add a button for the user to tap to enter the data.
To submit the information, the user taps the button. We use the currentState property from the GlobalKey to check if the Form is valid once the hit button.
The next step is to check if the Form is valid when the user tries to submit it. If that’s the case, show a success message. If the text field is empty, an error message will be displayed.
Conclusion
Flutter business app are one of the most demanding app development technology in the world. There are many approaches to validate forms in the User interface apart from those mentioned above. But this is the simplest method to validate Form in the flutter application.
