Flutter validation

A single form field. This widget maintains the current state of the form field, so that updates and validation errors are visually reflected in the UI . When used inside a Form, you can use methods on FormState to query or manipulate the form data as a whole. For example, calling FormState.

In this example, we are going to display the alert dialog with the current value of the text field when the user taps on a button.

and a Sign-Up button.