How To Create Forms in Flutter

Forms are essential for many apps, allowing users to input data and interact with the app. In this tutorial, we will show you how to create forms in Flutter and how to use them in your app. We will cover topics such as handling inputs, validating forms, and submitting forms. By the end of this article, you will have a complete code example for creating forms in Flutter.

What Are Forms and Why Are They Important?

Forms are essential for any app that needs to collect data from users. Forms are used for user registration, account settings, collecting payments, and more. They allow users to input data and interact with the app in a structured way.

Forms are important because they help to ensure that the data that users enter is valid and can be used by the app. For example, a form may require that a user enter a valid email address, or that a payment is made with a valid credit card. Without forms, it would be difficult to ensure that the data in the app is accurate and valid.

Handling Form Inputs in Flutter

In Flutter, forms are created using the Form widget. This widget takes a FormField widget as a child, which can be used to create individual form fields. For example, to create a text field, you can use the TextFormField widget.

Form(
  child: TextFormField(
    decoration: InputDecoration(
      labelText: 'Name',
    ),
  ),
)

You can also use other widgets such as CheckboxFormField and DropdownFormField to create other types of form fields.

Validating Forms in Flutter

Forms need to be validated to ensure that the data that is entered into them is valid. In Flutter, forms can be validated using the Form widget's validator property. This property takes a function that can be used to validate the form data.

For example, to validate a form field that requires a name to be entered, you can use the following code:

Form(
  child: TextFormField(
    decoration: InputDecoration(
      labelText: 'Name',
    ),
    validator: (value) {
      if (value.isEmpty) {
        return 'Name is required';
      }
      return null;
    },
  ),
)

In this example, if the field is empty, the validator will return an error message. Otherwise, it will return null, indicating that the form is valid.

Submitting Forms in Flutter

Once a form has been validated, it can be submitted. In Flutter, forms can be submitted using the Form widget's onSubmit property. This property takes a function that will be called when the form is submitted.

For example, the following code can be used to submit a form:

Form(
  onSubmit: (values) {
    // Submit the form here
  },
  child: TextFormField(
    decoration: InputDecoration(
      labelText: 'Name',
    ),
    validator: (value) {
      if (value.isEmpty) {
        return 'Name is required';
      }
      return null;
    },
  ),
)

In this example, when the form is submitted, the onSubmit function will be called with the form data. This function can then be used to submit the data to the server or perform some other action.

Complete Form Code Example in Flutter

Here is a complete code example for creating a form in Flutter:

Form(
  onSubmit: (values) {
    // Submit the form here
  },
  child: Column(
    children: <Widget>[
      TextFormField(
        decoration: InputDecoration(
          labelText: 'Name',
        ),
        validator: (value) {
          if (value.isEmpty) {
            return 'Name is required';
          }
          return null;
        },
      ),
      TextFormField(
        decoration: InputDecoration(
          labelText: 'Email',
        ),
        validator: (value) {
          if (value.isEmpty || !value.contains('@')) {
            return 'Invalid email address';
          }
          return null;
        },
      ),
      CheckboxFormField(
        validator: (value) {
          if (value == false) {
            return 'You must agree to the terms';
          }
          return null;
        },
        title: Text('Agree to Terms'),
        onChanged: (value) {},
      ),
      RaisedButton(
        onPressed: () {
          if (formKey.currentState.validate()) {
            formKey.currentState.save();
          }
        },
        child: Text('Submit'),
      ),
    ],
  ),
)

In this example, we have created a form with three fields - name, email, and a checkbox. We have also added validation for each field, and a RaisedButton for submitting the form.

Conclusion

In this tutorial, we have shown you how to create forms in Flutter and how to use them in your app. We have covered topics such as handling inputs, validating forms, and submitting forms. We have also provided a complete code example for creating forms in Flutter.