Solving the Horizontal Pager State Management in Jetpack Compose

Описание: Discover how to effectively manage state in a `Horizontal Pager` using Jetpack Compose, including maintaining the list state across updates.
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This video is based on the question https://stackoverflow.com/q/69257871/ asked by the user 'srituts' ( https://stackoverflow.com/u/16886925/ ) and on the answer https://stackoverflow.com/a/69279799/ provided by the user 'Phil Dukhov' ( https://stackoverflow.com/u/3585796/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Holding a List State in Horizontal Pager - Jetpack Compose

As developers explore the possibilities of building dynamic user interfaces in Android, Jetpack Compose has emerged as a powerful toolkit. One common challenge when working with the Horizontal Pager component is managing list state effectively, especially when it needs to be shuffled or updated frequently. In this guide, we will explore a common problem — how to maintain a list state in a Horizontal Pager — and break down the solution into clear, manageable steps.

The Problem

Imagine you’re building an application that requires users to interact with questions and answers presented in a horizontal scrolling format. You retrieve a list of questions from a database, shuffle them based on certain conditions, and present them using a favorite feature: the Horizontal Pager. However, after calling an update function to manage whether the user knows the answer, the list seems to refresh unpredictably, resulting in a new shuffled order that could confuse users.

What’s Happening?

The main issues that arise include:

The list of questions is shuffled every time an update function is called.

Users may lose context of what they’ve already seen or answered.

To maintain an uninterrupted flow, we need to hold on to the shuffled list and ensure the right questions are presented accordingly.

The Solution

To properly manage the list state in your Horizontal Pager, we need to ensure that we are maintaining the shuffled questions after every update. Here's how you can do that step-by-step:

Step 1: Modify Your ViewModel

Add a Mutable StateFlow for Filters: This allows you to keep track of the filter being applied (e.g., showing previously answered questions, new questions, random selections).

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Create a Map to Save Random IDs: Store the IDs of shuffled questions for each filter to easily restore them in future updates.

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Combine StateFlows to Generate the List of Questions: This will allow you to filter and shuffle your questions based on the chosen filter while retaining previously shuffled states.

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Step 2: Collect the Questions in Your Composable

In your HorizontalPager, instead of directly using quState, transition to using lstQuestions as shown below:

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Step 3: Update Functionality in the Card View

When users click to signify they know the answer, ensure you're sending that update back to the ViewModel correctly:

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Conclusion

By organizing the filtering and shuffling operations within your ViewModel and ensuring that you are consistently collecting the filtered list, you can maintain an intuitive user experience while interacting with your Horizontal Pager. This approach minimizes unexpected behavior when users engage with questions and ensures their progress remains coherent.

With these adjustments, your Jetpack Compose application will offer a smoother and more cohesive experience when using horizontal paging for your lists of questions and answers.

Happy coding!