Working with forms in Flutter is an essential task for many applications, as they are the main way to collect user information. As of Flutter 1.17, Flutter provides a powerful and flexible way to manage forms, including validation, event handling, and integration with other parts of Flutter.
To start working with forms in Flutter, you need to understand the basics of form widgets. In Flutter, a form is represented by the Form widget which contains one or more FormField widgets.
The FormField widgets are the basis for most of the data entry widgets in Flutter. They handle data validation, event handling, and integration with the Form widget. Some of the more common data entry widgets based on FormField include TextFormField, DropdownButtonFormField and CheckboxListTile.
To create a form in Flutter, you first create an instance of the Form widget and then add the FormField widgets you need. Each FormField has a validator which is a function that takes the current value of the field and returns an error string if the value is not valid, or null if the value is valid .
In addition, each FormField has an onSaved which is a function that is called when the form is saved. This function takes the current value of the field and can be used to save the value somewhere, like a database or the cloud.
To save a form, you call the save method on the Form. This causes Form to call onSaved on each FormField in order. If any validator returns an error string, the Form will not be saved and the error will be shown to the user.
Now, let's talk about how to test forms in Flutter. Flutter provides two ways to test your code: unit tests and integration tests.
Unit tests are used to test a single function or method. They're quick to write and run, and they're great for testing business logic. In the context of a form, you can write unit tests for its validators and onSaved functions.
To write a unit test in Flutter, you use the test package. First, you create a test function that is given a name and role. The test function should contain some code that calls the function or method you are testing and verifies that the result is what you expect.
Integration tests are used to test how various parts of your application work together. They are slower to write and run than unit tests, but they are great for testing end-user functionality. In the context of a form, you can write integration tests that populate the form, press the submit button, and verify that the result is what you expect.
To write an integration test in Flutter, you use the flutter_test package. First, you create a test function that is given a name and role. The test function should contain some code that interacts with the application, such as filling out a form and pressing a button, and then verifies that the result is what you expect.
In summary, working with forms in Flutter is an essential task for many applications. Flutter provides a powerful and flexible way to manage forms, including validation, event handling, and integration with other parts of Flutter. Furthermore, Flutter provides two ways to test your code: unit tests and integration tests.
