Initialize useState Hook with Asynchronous Data in Flutter Hooks

Описание: Learn how to efficiently initialize the `useState` hook in Flutter Hooks with values retrieved asynchronously, using SharedPreferences as an example.
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This video is based on the question https://stackoverflow.com/q/64108214/ asked by the user 'swedishcheef' ( https://stackoverflow.com/u/14414411/ ) and on the answer https://stackoverflow.com/a/66531970/ provided by the user 'hyobbb' ( https://stackoverflow.com/u/13881052/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Flutter Hooks: Initializing useState with Asynchronous Data

If you've recently dove into Flutter Hooks, you may have encountered a common scenario: initializing the useState hook with an asynchronous value. This situation often arises when data needs to be fetched from sources like SharedPreferences. You may find yourself wondering how to effectively manage this asynchronous fetching while adhering to the best practices of Flutter development. In this post, we’ll walk you through a clear and efficient way to achieve this using HookBuilder.

The Problem

To illustrate, let's consider your specific example. Typically, you would initialize a useState hook like this:

[[See Video to Reveal this Text or Code Snippet]]

However, when the value is not immediately available (in your case, it is fetched from SharedPreferences asynchronously), your initialization needs to reflect that. You might be tempted to do something like:

[[See Video to Reveal this Text or Code Snippet]]

But this is not straightforward and won't work as expected, since useState cannot directly handle asynchronous values.

The Solution: Using HookBuilder and useFuture

To resolve this issue, we'll utilize the HookBuilder in combination with the useFuture hook. Here is how you can structure it:

Step 1: Use useMemoized

First, you'll want to call your asynchronous function using useMemoized. This allows you to store the future value and utilize it multiple times without invoking the function every time the widget rebuilds.

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Use useFuture

Next, you can handle the asynchronous fetch result using useFuture, which monitors the state of the future you created.

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Conditionally Render with HookBuilder

Now, you can conditionally render your widget based on whether the data has been retrieved:

[[See Video to Reveal this Text or Code Snippet]]

Full Code Example

Putting this all together, your widget can look something like this:

[[See Video to Reveal this Text or Code Snippet]]

Key Takeaways

Asynchronous Data Initialization: Instead of trying to pass asynchronous values directly to useState, utilize useFuture and HookBuilder.

Use of useMemoized: This will ensure that your asynchronous function is called only once unless its dependencies change.

Conditional Rendering: Always check if data is available before proceeding with logic that depends on it; this prevents runtime errors.

By following these steps, you'll have a robust solution for initializing useState with asynchronous data in Flutter Hooks. Happy coding!