Mastering Keyboard Focus with FocusNode: Pitfalls and Proven Solutions In Flutter Part 1

In my recent project, I had the opportunity to work with the FocusNode class in my Flutter application. Working with FocusNodes taught me a few valuable tricks that I’d like to share in this article.

If you’re new to Flutter, you might be wondering what a FocusNode is. Simply put, it’s a class in Flutter that allows a stateful widget to obtain keyboard focus and handle keyboard events. Since FocusNodes are long-lived objects with a lifecycle that needs to be managed, they are typically used in stateful widgets.

FocusNodes are persistent objects, which means they need to be explicitly terminated before they are destroyed. They form a focus tree, which is a collection of widgets that implement focus.

The primary purpose of a FocusNode is to focus and unfocus widgets, particularly text fields, in the widget tree. If you want to automatically focus a text field as soon as the page loads, Flutter provides a straightforward way to accomplish this.

const TextField(
  autofocus: true,
),

There are scenarios where you may need to focus a textField with a button click, and luckily, it’s a straightforward process. By utilizing the FocusNode, you can identify a specific TextField within the widget tree. It’s worth noting that multiple TextFields can utilize a single FocusNode, effectively marking these TextFields throughout the entire widget tree. This mechanism enables us to easily focus a particular TextField by simply clicking a button.

TextField(
  focusNode: specialFocusNode,
),
ElevatedButton(
  onPressed: () => specialFocusNode.requestFocus(),
  child: const Text('Focus'),
),

By utilizing the specialFocusNode below, we can mark the TextField throughout the widget tree, granting us access to its focus ability from anywhere within our app. To request focus on the TextField from inside an ElevatedButton, the corresponding code would resemble the following:

class Focus extends StatefulWidget {
  const Focus({Key? key}) : super(key: key);

  @override
  State<Focus> createState() => _FocusState();
}

class _FocusState extends State<Focus> {
  late FocusNode specialFocusNode;
  @override
  void initState() {
    //create the FocusNode as soon as the page is created
    super.initState();
    specialFocusNode = FocusNode();
  }

  @override
  void dispose() {
    //destroys the FocusNode as soon as the page is destroyed
    //because it is a long-lived object
    specialFocusNode.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Text Field Focus'),
      ),
      body: Padding(
        padding: const EdgeInsets.all(20.0),
        child: Column(
          children: [
            const TextField(
              //automatically setting the focus as soon as the page comes into view
              autofocus: true,
            ),
            TextField(
              //TextField with a FocusNode
              focusNode: specialFocusNode,
            ),
            ElevatedButton(
              //giving focus to the TextField with the specified FocusNode
              onPressed: () => specialFocusNode.requestFocus(),
              child: const Text('Focus'),
            ),
          ],
        ),
      ),
    );
  }
}

A FocusNode is a persistent object with a lifecycle that can only be managed by a stateful widget, and that’s where its true power lies.

In my project, I encountered a more complex scenario that required a different approach than the examples mentioned earlier. Let me provide you with a brief overview of what I aimed to accomplish.

In this particular project, I was tasked with creating a pop-up screen for verification codes. The screen consisted of four TextFields, each allowing a maximum length of one character. The layout resembled something like this:

The functionality required for this project was relatively straightforward: when the user enters a character in one of the four verification code TextFields, the focus should automatically shift to the next TextField. Additionally, if the user taps the delete button, the focus should move back to the previous TextField. Sounds easy, right?

Indeed, accomplishing the forward focus shift was a relatively simple task. Once all four TextFields were filled, the user could delete and start again. However, a significant challenge arose when attempting to enable deletion in specific TextFields, such as the second or third TextField. Unfortunately, the user was required to fill all four TextFields before deletion could occur.

This limitation posed a considerable obstacle and presented an area that required further exploration and improvement.

After conducting thorough research, I found that implementing this particular feature posed a challenge in Flutter. It became evident that Flutter does not provide a straightforward solution to determine when the delete button on the keyboard is pressed. However, don’t lose hope just yet! There are workarounds available, as well as packages that can assist in achieving the desired functionality.

By exploring alternative approaches and leveraging relevant packages, you can overcome this hurdle and accomplish the desired behavior for your verification code input. These resources provide valuable tools and methods to address the limitations present in Flutter’s default functionality.

In my upcoming post, I will delve deeper into the available options and explore how these workarounds and packages can aid in achieving the desired verification code input behavior. Stay tuned for a comprehensive exploration of the solutions that can overcome the limitations posed by Flutter’s default functionality.

In conclusion, working with the FocusNode class in Flutter has revealed both its power and limitations. While it offers a reliable means to obtain keyboard focus and manage focus within a widget tree, certain scenarios, such as achieving specific focus behavior with verification code input, may require additional exploration.

Remember, challenges are not roadblocks but opportunities for innovation. The absence of a direct solution doesn’t mean we should give up; instead, it pushes us to explore alternative approaches and leverage the vast resources available in the Flutter community.