Скачать или смотреть How to Create LiveData for RecyclerView Items from LiveData of Room Entities in Android's MVVM

Learn how to transform `LiveData List Symptom ` into `LiveData List SymptomItem ` using Kotlin Flow in Android MVVM. Perfect for beginners in Android development!
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This video is based on the question https://stackoverflow.com/q/64412203/ asked by the user 'Oktawian' ( https://stackoverflow.com/u/9495357/ ) and on the answer https://stackoverflow.com/a/64414622/ provided by the user 'zOqvxf' ( https://stackoverflow.com/u/1744889/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Create LiveData for RecyclerView Items from LiveData of Room Entities in Android's MVVM

In the world of Android development, implementing the MVVM architecture along with Room can sometimes be challenging, especially when you're aiming to display a list of items in a RecyclerView. If you’ve started working on an application that handles user-selected symptoms, you're likely faced with the question of how to create a LiveData<List<SymptomItem>> from a LiveData<List<Symptom>>. If you've been struggling with this issue, we're here to provide clarity and a concrete solution.

Understanding the Problem

You're working with a Room Entity class called Symptom, which represents a data model for symptoms with an ID and a name. You also have a basic setup involving SymptomDao, SymptomRepository, and SymptomsViewModel. You desire to generate a list of SymptomItem objects that not only includes information from the Symptom but also maintains the state of a checkbox indicating whether a symptom is selected or not.

The Challenge

The main challenge is maintaining the state of each checkbox (checked or unchecked) through configuration changes (like screen rotations), while converting the LiveData<List<Symptom>> to LiveData<List<SymptomItem>>.

The Solution

To achieve this, we’ll introduce Kotlin's Flow and use a mutable state flow to manage the checkbox selections effectively. Let's break down this solution into manageable steps.

Step 1: Update Your DAO to Use Flow

Firstly, we'll modify the SymptomDao to provide a Flow of symptoms instead of a LiveData. This allows for more reactive programming and easier management of UI updates.

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Step 2: Adjust Your Repository

Now, we need to make sure your repository can flow this data too. Update your SymptomRepository accordingly:

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Step 3: Update Your ViewModel

The heart of the solution lies within the SymptomsViewModel. Here’s how to set it up:

Use Flow for the Symptoms List: We will collect the symptoms via a StateFlow.

Combine with Checked IDs: Combine the lists of symptoms with the selection state.

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Step 4: Wire It Up in Your Fragment

In the Fragment where you have your RecyclerView, you will want to observe your getSymptomsItems() function and update your adapter accordingly.

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Conclusion

By following these steps, you will effectively convert your LiveData<List<Symptom>> into LiveData<List<SymptomItem>> while maintaining checkbox states in a RecyclerView. This pattern leverages the power of Kotlin Flow and allows you to efficiently manage data streams in your Android applications.

Note: The code provided here is a guideline, and you might need to make small adjustments for successful compilation.

By implementing this approach, you're building a solid foundation for managing dynamic data in your Android apps while adhering to the principles of MVVM architecture. Happy coding!