Building the Form UI: Crafting a Feedback Form in Flutter

5.4.2 Building the Form UI

Creating an intuitive and functional user interface for forms is a crucial aspect of app development. In this section, we will guide you through the process of building a feedback form using Flutter. This involves designing the form layout, adding various input fields, and managing the form’s state effectively. By the end of this section, you will have a comprehensive understanding of how to construct a user-friendly form interface in Flutter.

Designing the Form Layout

The layout of a form is essential for ensuring that users can easily navigate and complete it. In Flutter, we use layout widgets such as Column, Row, and Padding to organize input fields and provide appropriate spacing. Let’s start by structuring our form using these widgets.

Structuring the Form with Layout Widgets

To create a well-organized form, we will use a Column widget to stack our input fields vertically. We will also use Padding to add space around the form, making it visually appealing and user-friendly.

Padding(
  padding: const EdgeInsets.all(16.0),
  child: Form(
    key: _formKey,
    child: Column(
      children: <Widget>[
        TextFormField(
          decoration: InputDecoration(labelText: 'Name'),
          validator: validateNotEmpty,
          onSaved: (value) {
            _name = value!;
          },
        ),
        TextFormField(
          decoration: InputDecoration(labelText: 'Email'),
          validator: validateEmail,
          onSaved: (value) {
            _email = value!;
          },
        ),
        // Additional form fields will be added here
      ],
    ),
  ),
);

Explanation:

• Padding: We use the Padding widget to add a uniform margin around the form, enhancing its appearance and usability.
• Form: The Form widget is a container for form fields. It uses a GlobalKey to manage the form’s state, allowing us to validate and save the form data.
• Column: This widget stacks its children vertically, making it ideal for organizing form fields.
• TextFormField: These are the input fields for the form. We will add more fields as we progress.

Adding Input Fields

Input fields are the core components of any form. In our feedback form, we will include fields for the user’s name, email, a rating selection, and a comments section.

Name and Email Fields

The TextFormField widget is perfect for capturing text input. We will use it to create fields for the user’s name and email, complete with validation logic to ensure data integrity.

TextFormField(
  decoration: InputDecoration(labelText: 'Name'),
  validator: validateNotEmpty,
  onSaved: (value) {
    _name = value!;
  },
);

TextFormField(
  decoration: InputDecoration(labelText: 'Email'),
  validator: validateEmail,
  onSaved: (value) {
    _email = value!;
  },
);

Explanation:

• InputDecoration: Provides a label for the input field, guiding the user on what to enter.
• Validator: A function that checks the input’s validity. validateNotEmpty ensures the field is not empty, while validateEmail checks for a valid email format.
• onSaved: A callback that saves the input value when the form is submitted.

Rating Selection

For the rating input, we can choose between radio buttons or a slider. Each method has its advantages, and the choice depends on the desired user experience.

Radio Buttons Example:

Column(
  crossAxisAlignment: CrossAxisAlignment.start,
  children: <Widget>[
    Text('Rate our service:', style: TextStyle(fontSize: 16)),
    Row(
      children: <Widget>[
        Radio<int>(
          value: 1,
          groupValue: _rating,
          onChanged: (int? value) {
            setState(() {
              _rating = value!;
            });
          },
        ),
        Text('1'),
        Radio<int>(
          value: 2,
          groupValue: _rating,
          onChanged: (int? value) {
            setState(() {
              _rating = value!;
            });
          },
        ),
        Text('2'),
        // Continue for ratings 3 to 5
      ],
    ),
  ],
);

Slider Example:

Column(
  crossAxisAlignment: CrossAxisAlignment.start,
  children: <Widget>[
    Text('Rate our service:', style: TextStyle(fontSize: 16)),
    Slider(
      value: _rating.toDouble(),
      min: 1.0,
      max: 5.0,
      divisions: 4,
      label: '$_rating',
      onChanged: (double newValue) {
        setState(() {
          _rating = newValue.round();
        });
      },
    ),
  ],
);

Explanation:

• Radio Buttons: Allow users to select a discrete value. Each Radio widget represents a choice, and the groupValue links them together.
• Slider: Provides a continuous range of values. The divisions property specifies the number of discrete intervals.

Comments Section

To capture user comments, we will use a multi-line TextFormField. This allows users to provide detailed feedback.

TextFormField(
  decoration: InputDecoration(
    labelText: 'Comments',
    alignLabelWithHint: true,
    border: OutlineInputBorder(),
  ),
  maxLines: 4,
  onSaved: (value) {
    _comments = value!;
  },
);

Explanation:

• Multi-line Input: The maxLines property allows the field to expand, accommodating longer text.
• OutlineInputBorder: Enhances the field’s appearance with a border.

Implementing Controlled Input Widgets

For greater control over input fields, we can use TextEditingController. This allows us to programmatically manipulate the text within the fields.

final TextEditingController _nameController = TextEditingController();
final TextEditingController _emailController = TextEditingController();

@override
void dispose() {
  _nameController.dispose();
  _emailController.dispose();
  super.dispose();
}

TextFormField(
  controller: _nameController,
  decoration: InputDecoration(labelText: 'Name'),
  validator: validateNotEmpty,
);

Explanation:

• TextEditingController: Manages the text being edited. It can be used to set initial values, clear the field, or retrieve the current text.
• dispose: It’s crucial to dispose of controllers to free up resources when they are no longer needed.

Visualizing the Form Structure

To better understand the form’s structure, let’s use a Mermaid.js diagram to visualize the components and their relationships.

    flowchart LR
	  A[Building the Form UI] --> B[Form Layout]
	  B --> C[Column]
	  B --> D[Padding]
	  
	  A --> E[Input Fields]
	  E --> E1[Name TextFormField]
	  E --> E2[Email TextFormField]
	  E --> E3[Rating Selection]
	  E --> E4[Comments TextFormField]
	  
	  A --> F[State Management]
	  F --> F1[TextEditingController]
	  F --> F2[Form Key]

Diagram Explanation:

• Form Layout: Shows the use of Column and Padding to organize the form.
• Input Fields: Illustrates the different types of input fields used in the form.
• State Management: Highlights the use of TextEditingController and Form Key for managing form state.

Best Practices and Common Pitfalls

• Consistent Spacing: Use Padding and SizedBox to ensure consistent spacing between form elements.
• Validation: Always validate user input to prevent errors and ensure data integrity.
• State Management: Use setState judiciously to update the UI only when necessary, avoiding unnecessary rebuilds.
• Accessibility: Ensure that all form elements are accessible, with appropriate labels and hints.

Further Exploration

• Official Documentation: Refer to the Flutter documentation for more details on form widgets and state management.
• Open-Source Projects: Explore open-source Flutter projects on GitHub to see how others implement forms.
• Online Courses: Consider taking courses on platforms like Udemy or Coursera to deepen your understanding of Flutter development.

Conclusion

Building a form UI in Flutter involves a combination of layout design, input field configuration, and state management. By following the steps outlined in this section, you can create a functional and user-friendly feedback form. Remember to validate input, manage state effectively, and ensure accessibility for all users.

Quiz Time!