“PageStorage: A Simple Guide to Saving and Restoring Page State in Flutter”

Introduction

Flutter is a popular open-source UI toolkit for building native mobile apps for iOS and Android. It is known for its fast performance, expressive and flexible APIs, and the ability to create complex and visually appealing interfaces. One of the challenges of building apps in Flutter is how to preserve the state of the UI between transitions, especially when navigating between pages. The PageStorage widget provides a simple solution to this problem. Okay! Let’s Get Started!

What is PageStorage Widget?

PageStorage is a widget that allows you to save and restore the state of a particular widget tree within a PageStorageBucket. A PageStorageBucket is simply a container that holds PageStorage objects. Each PageStorage object can store the state of a widget tree and make it available across different pages or routes.

Why Use PageStorage Widget?

The PageStorage widget is particularly useful when building apps with a large number of pages that can change their state dynamically. For example, if you have a tabbed interface with different pages displaying different data, you can use the PageStorage widget to store and restore the state of each page as the user navigates between them. This ensures that the user’s experience is seamless and the UI remains consistent, even if the app is killed or restarted.

How to Use PageStorage Widget?

Using the PageStorage widget is straightforward. Simply wrap the widget tree you want to save the state of with a PageStorage widget and specify the PageStorageBucket to store the state in.

PageStorage can be used in various scenarios where you want to preserve the state of a widget tree between transitions, some of these cases include:

1. Tabbed Interfaces: If you have a tabbed interface with multiple pages that display different data, you can use the PageStorage widget to store and restore the state of each page as the user navigates between them.

Here’s an example:

class MyTabs extends StatefulWidget {
  const MyTabs({super.key});

  @override
  State<MyTabs> createState() => _MyTabsState();
}

class _MyTabsState extends State<MyTabs> with SingleTickerProviderStateMixin {
 late TabController _controller;

  @override
  void initState() {
    super.initState();
    _controller = TabController(vsync: this, length: 2);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: PageStorage(
        bucket: PageStorageBucket(),
        child: TabBarView(
          controller: _controller,
          children: [
            PageStorage(
              child: MyPage1(),
              bucket: PageStorageBucket(),
            ),
            PageStorage(
              child: MyPage2(),
              bucket: PageStorageBucket(),
            ),
          ],
        ),
      ),
      bottomNavigationBar: TabBar(
        controller: _controller,
        tabs: const [
          Tab(text: 'Page 1'),
          Tab(text: 'Page 2'),
        ],
      ),
    );
  }
}

In this example, we are using the PageStorage widget to store the state of two pages (MyPage1 and MyPage2) within a TabBarView. The state of each page is stored in a separate PageStorage object and made available across different tabs using a PageStorageBucket.

2. Form Input: If you have a form with multiple fields, you can use the PageStorage widget to store and restore the state of each field as the user inputs data.

Here’s an example:

class MyForm extends StatefulWidget {
  const MyForm({super.key});

  @override
  State<MyForm> createState() => _MyFormState();
}

class _MyFormState extends State<MyForm> {
  final _formKey = GlobalKey<FormState>();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Form(
        key: _formKey,
        child: PageStorage(
          bucket: PageStorageBucket(),
          child: Column(
            children: [
              TextFormField(
                decoration: const InputDecoration(labelText: 'Name'),
              ),
              TextFormField(
                decoration: const InputDecoration(labelText: 'Email'),
              ),
              TextFormField(
                decoration: const InputDecoration(labelText: 'Password'),
              ),
            ],
          ),
        ),
      ),
    );
  }
}

In this example, we are using the PageStorage widget to store the state of a Form widget containing three TextFormFields. The state of each field is stored in a single PageStorage object and made available across different pages or routes.

PageStorageKey?

The PageStorageKey is used to uniquely identify a widget within the PageStorage. The purpose of a PageStorageKey is to provide a stable identifier for the widget so that its state can be stored and retrieved in a PageStorage object.

For example, consider a scenario where you have multiple instances of the same form in different pages. Without a PageStorageKey, the state of each form would be stored in the same PageStorage object and would overwrite each other. However, by assigning a unique PageStorageKey to each form, you can ensure that their states are stored and retrieved separately.

Here’s an example:

class MyForm extends StatefulWidget {
  final int index;

 const MyForm({Key? key, required this.index}) : super(key: key);

  @override
  State<MyForm> createState() => _MyFormState();
}

class _MyFormState extends State<MyForm> {
  final _formKey = GlobalKey<FormState>();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Form(
        key: _formKey,
        child: PageStorage(
          bucket: PageStorageBucket(),
          key: PageStorageKey(widget.index),
          child: Column(
            children: [
              TextFormField(
                decoration: const InputDecoration(labelText: 'Name'),
              ),
              TextFormField(
                decoration: const InputDecoration(labelText: 'Email'),
              ),
              TextFormField(
                decoration: const InputDecoration(labelText: 'Password'),
              ),
            ],
          ),
        ),
      ),
    );
  }
}

In this example, we are using the PageStorageKey to identify a form with a unique index number. This allows us to store the state of each form instance separately in the PageStorage.

In conclusion

The PageStorage widget is a powerful tool for preserving the state of a widget tree between transitions in Flutter. This widget is particularly handy in scenarios where you want to preserve the state of your UI across different pages or routes, such as when navigating between tabs or switching between different parts of your app. The PageStorage widget uses a key-value store to persist the state of your widgets, and the PageStorageKey to provide a stable identifier for each widget. This makes it easy to store and retrieve the state of your UI, including scroll positions, form data, and other important information.

Whether you are building a small app or a large enterprise system, the PageStorage widget provides a simple and efficient way to maintain the state of your UI. By using PageStorage, you can provide your users with a more seamless and intuitive experience, and build more robust and user-friendly UIs in Flutter.

#Flutter #PageStorage #UIStateManagement #AppDevelopment #MobileDevelopment #FlutterDev #FlutterUI #FlutterApps #FlutterWidgets