Building Accessible Flutter Web Apps

10 min readApr 18, 2024

Reach a wider audience and create inclusive experiences by following these essential accessibility practices..

In the world of web development, accessibility refers to the practice of designing and building web experiences that are usable by everyone, regardless of their abilities. This includes users with visual, auditory, motor, or cognitive impairments. By prioritizing accessibility, we can create web apps that are inclusive and reach a wider audience.

While Flutter provides a solid foundation for building web apps, its accessibility features in the web context currently follow an opt-in approach. This means that certain functionalities need to be explicitly enabled by the developer to ensure a fully accessible experience.

This article will guide you through everything you need to know about building accessible web applications with Flutter. We’ll explore core concepts like the accessibility tree, Semantics widgets, and ARIA attributes. We’ll then delve into practical techniques for enhancing accessibility in your Flutter web projects, including creating accessible custom widgets and ensuring proper keyboard navigation. Finally, we’ll discuss how to test and verify the accessibility of your app, ensuring a smooth and inclusive experience for all users.

Free Access to the Story: https://medium.com/@aaronreddixx/building-accessible-flutter-web-apps-343b452401a0?source=friends_link&sk=1134cc135dcbf2b4faa22c2b55339f7e

Core Concepts

Building accessible Flutter web apps requires a solid understanding of the underlying mechanisms. Let’s explore some key concepts that play a crucial role in achieving this goal:

1. Accessibility Tree

When it comes to web accessibility, assistive technologies (AT) like screen readers play a crucial role. These tools rely on a structured representation of the web page content to understand the layout and functionality. This structure is called the accessibility tree.

Imagine a map that outlines the structure and hierarchy of your web app’s content. This map, called the accessibility tree, serves as a critical tool for assistive technologies (AT) like screen readers. AT software relies on the accessibility tree to understand the elements on the screen, their relationships, and how users can interact with them.

The good news is that Flutter automatically generates an accessibility tree for many common widgets like Buttons, text fields, and Text elements. This tree reflects the inherent structure and functionality of these widgets, making them readily interpretable by AT.

Here’s a code snippet demonstrating a simple Flutter layout with a Button and Text widget:

In this example, Flutter automatically creates an accessibility tree that recognizes the “Text” widget as a label and the “ElevatedButton” as a button with the text “Click Me”. This information is then communicated to AT software, allowing users to navigate and interact with these elements effectively.

2. Semantics Class

The Semantics class in Flutter serves as a powerful tool for enhancing the accessibility of custom widgets and UI elements in your web app. It allows you to explicitly define the Semantics of your widget, providing additional information for AT software.

Here’s how the Semantics class works:

Imagine wrapping your custom widget with the Semantics widget. This wrapper acts like a label, conveying the meaning and functionality of your custom element to AT software.

Within the Semantics widget, you can define various properties to provide specific details. Some key properties include:

label: This property specifies a text description of the element, similar to an alt text for images.
hint: This property provides additional context or instructions for interacting with the element.
semanticsFlags: This property allows you to set various flags that define the behavior of the element from an accessibility perspective. For example, you can set flags to indicate if the element is a button, a checkbox, or a header.

By utilizing these properties effectively, you can transform your custom widget into a fully accessible element within the accessibility tree.

Here’s an example of how to use the Semantics class to create an accessible custom widget representing a star rating:

In this example, we wrap each star icon with a Semantics widget. We define the label property to describe the filled or unfilled state of the star. Additionally, we set the hint property to provide instructions for interacting with the star (tapping to set rating). This ensures that screen readers can understand the purpose of each star icon and how users can interact with them to set the rating.

By effectively leveraging the Semantics class, you can empower your custom widgets to participate seamlessly in the accessibility tree, creating a more inclusive experience for all users.

3. ARIA Attributes

While the Semantics class provides a powerful way to enhance accessibility for custom widgets, Flutter also leverages another crucial accessibility standard: ARIA (Accessible Rich Internet Applications) attributes.

ARIA attributes are a set of HTML attributes designed to improve the accessibility of web content for users with disabilities. These attributes provide additional information about the functionality and behavior of elements, further enriching the accessibility tree for AT software.

The good news is that Flutter automatically injects relevant ARIA attributes for many common widgets. For example, a Checkbox widget automatically includes ARIA attributes that identify it as a checkbox and indicate its current checked state.

However, for more complex scenarios or custom widgets, you might need to consider adding ARIA attributes manually. This can be achieved by setting the child property of the Semantics widget to a widget that includes the desired ARIA attributes.

Here’s an example of using a Semantics widget with a custom RichText element to include an ARIA attribute for a live region:

In this example, we use a RichText widget to display text with different styles. We set the semanticsLabel property on the RichText itself to describe the overall content. Additionally, we set the semanticsLabel property on the italicized text span to provide a more specific description for that part.

Finally, we wrap the entire RichText widget with a Semantics widget. Here, we set the ariaLive property to AriaLiveOption.assertive, indicating that this region will contain important updates that require immediate announcement by screen readers.

By strategically using ARIA attributes within the Semantics widget, you can provide a richer layer of information for AT software, further enhancing the accessibility of your custom UI elements.

Enhancing Accessibility in Flutter Web Apps

Equipping yourself with the core concepts of accessibility trees, the Semantics class, and ARIA attributes is the foundation for building truly accessible Flutter web apps. Now, let’s delve into practical techniques you can employ to elevate the accessibility of your projects:

1. Utilizing Built-in Accessibility Features

Flutter provides a wide range of widgets that, inherently, offer good accessibility. These widgets come pre-equipped with appropriate semantics and ARIA attributes, making them readily interpretable by AT software.

Here are some examples:

Buttons: ElevatedButton, TextButton, IconButton — These buttons automatically convey their functionality and allow for keyboard interaction.
Text Fields: TextField, TextFormField — These widgets come with built-in labels and support for screen reader interaction.
Form Elements: Checkbox, Radio, Slider — These elements have proper semantics and ARIA attributes associated with them.

By leveraging these built-in widgets whenever possible, you can establish a strong foundation for accessibility in your Flutter web app.

2. Creating Accessible Custom Widgets

For custom UI elements or functionalities, the Semantics class becomes your best friend. As discussed earlier, you can wrap your custom widget with Semantics and define properties like label, hint, and semanticsFlags to provide clear descriptions and functionalities for AT software.

Here’s an example of creating an accessible custom widget for a progress bar:

In this example, the Semantics widget provides a clear description of the progress bar’s purpose and its current value. Additionally, we set properties like increasedValue and decreasedValue to provide context for screen readers when the progress changes.

Note: For any custom widget you create, consider its accessibility from the outset. Utilize the Semantics class effectively to ensure it integrates seamlessly into the accessibility tree.

3. Keyboard Navigation

For users with motor limitations or who rely on screen readers, keyboard navigation is paramount. It allows them to efficiently move around the web app and interact with elements using the keyboard. In Flutter web apps, ensuring proper keyboard navigation is crucial for achieving accessibility.

Here are some key aspects to consider:

Focus Management: Flutter employs a focus system that determines which element on the screen is currently receiving user input. By default, users can navigate between focusable elements using the Tab key and Shift+Tab key.
Keyboard Shortcuts: You can define keyboard shortcuts for specific actions within your app. This allows users to perform actions quickly without relying on the mouse. Flutter provides the Shortcuts widget to define these shortcuts and associate them with specific functionalities.

Here’s how you can ensure proper keyboard navigation in your Flutter web app:

Focusable Widgets: Use widgets that are inherently focusable, such as TextField, Button, or custom widgets wrapped with Focus widget. This allows users to tab through them and interact using the keyboard.
Logical Focus Order: Arrange the focus order of your elements in a logical sequence that reflects the natural flow of your app. This ensures a smooth and intuitive navigation experience for keyboard users.
Keyboard Shortcuts: Consider implementing keyboard shortcuts for frequently used actions. This can significantly improve efficiency for users who primarily rely on keyboard navigation.

Here’s a code example demonstrating a simple login form with proper focus management and a keyboard shortcut:

In this example, the TextField widgets are inherently focusable, and we set autofocus: true on the username field to provide initial focus. The ElevatedButton is also focusable and includes a keyboard shortcut (Ctrl+Enter) for login functionality.

By prioritizing focus management, logical focus order, and implementing keyboard shortcuts where appropriate, you can ensure your Flutter web app provides a seamless and efficient experience for users who rely on keyboard navigation.

Testing and Verification

Building accessible Flutter web apps is just one part of the equation. To ensure a truly inclusive experience, you need to rigorously test and verify the accessibility of your app. Here are some key strategies:

1. Accessibility Tools

A variety of accessibility testing tools can help you identify potential issues in your Flutter web app. These tools can scan your web pages and highlight areas that might not be accessible to users with disabilities.

Some popular options include:

Chrome DevTools Accessibility Audit: This built-in tool in Chrome allows you to analyze your web page and identify accessibility violations against WCAG (Web Content Accessibility Guidelines) standards.
WAVE Web Accessibility Evaluation Tool: This free online tool by WebAIM provides a comprehensive evaluation of your web page’s accessibility.
Axe for Web: This open-source accessibility testing library can be integrated into your development workflow for automated testing.

By utilizing these tools, you can systematically identify areas for improvement and ensure your Flutter web app adheres to accessibility best practices.

Here’s how you can use Chrome DevTools Accessibility Audit:

Open your Flutter web app in Chrome.
Right-click anywhere on the page and select “Inspect”.
Navigate to the “Audits” tab within the DevTools panel.
Select the “Accessibility” audit and run it.

The audit will analyze your web page and provide a report highlighting any accessibility violations. You can then click on each violation to understand the issue and implement the necessary fixes.

2. Screen Reader Testing

While accessibility tools are valuable, there’s no substitute for testing with real screen readers. This allows you to experience your app firsthand from the perspective of a user who relies on a screen reader.

Conclusion

Building accessible Flutter web apps requires a commitment to inclusivity and a user-centric approach. By understanding core concepts like the accessibility tree, the Semantics class, and ARIA attributes, you can empower your custom widgets and UI elements to participate seamlessly in the accessibility experience.

This article provides practical techniques for enhancing accessibility in your Flutter web projects. We explored utilizing built-in accessibility features, creating accessible custom widgets, and ensuring proper keyboard navigation. Additionally, we discussed the importance of testing and verification using accessibility tools and screen reader testing.

Prioritizing accessibility is not just about adhering to guidelines; it’s about creating a web app that everyone can use and enjoy. As Flutter web development continues to evolve, we can expect further advancements in accessibility features. However, the core principles outlined in this article remain fundamental for building inclusive experiences today.