Getting Started with Paging Library v3 in Android

When building Android apps that show long lists of information—like news articles, product listings, or social media posts—developers often use a RecyclerView. This component helps display a list of items efficiently. But if the list is very large, loading all the data at once can slow down the app, waste internet data, and use too much memory. Imagine an app that loads hundreds or thousands of items from the internet. Even though only a few items are visible on the screen at any moment, the app may try to download and store everything right away. This is inefficient and leads to Slower performance, More data usage, Higher memory consumption and Poor user experience. The solution to this problem was Pagination.

What is Pagination?

Pagination means breaking down the data into smaller parts, or "pages," and loading them only when needed. For example, you load the first 20 items, and when the user scrolls to the bottom, you load the next 20. This is how apps like Instagram or Twitter show more content as you scroll. To help developers implement pagination easily and efficiently, Google introduced the Paging 3 library as part of Android Jetpack. It was released around the time of Android 11 Beta.

How Paging Works?

The following steps are how the Paging library works:

1. The app shows a small portion of data (for example, 20 items).
2. As the user scrolls down, the app detects that the user is near the bottom.
3. The app automatically fetches the next "page" of data (another 20 items).
4. This continues as the user keeps scrolling, giving the experience of an "infinite list."

Advantages of using Paging Library

The Paging 3.0 version is very unique in comparison to the previous versions of the Android Paging library. Following are the new features and their advantages:

• It supports error handling with built-in refresh and retry features.
• It works perfectly with Kotlin Coroutines, Flow, LiveData, and RxJava.
• It allows easy addition of loading headers, footers, and list separators.
• It caches data in memory to improve performance and reduce resource usage.
• It automatically manages page keys for next and previous data loads.
• It prevents duplicate API calls to save bandwidth and system resources.
• It improves the repository layer with easy cancellation and cleaner APIs.

Dependency for Paging Library

Apply the Paging 3.0 library in a project by adding its implementation in the Gradle Scripts >build.gradle.kts (Module :app) file to import the Paging components.

dependencies {
    ...
    implementation("androidx.paging:paging-runtime:3.3.6")
}

Check the latest version of paging library here.

The Architecture of Paging Library

The Paging library is designed to follow the recommended Android architecture, which separates the app into different layers. This helps keep the code clean, organized, and easier to maintain. The Paging library mainly works across three layers of an app:

1. Repository layer
2. ViewModel layer
3. UI layer

1. Repository Layer - This layer handles where and how the data is loaded. It uses two main components:
   • PagingSource: Defines the source of data and fetches it, either from a local database or from the internet (API).
   • RemoteMediator: Manages paging when you're combining data from multiple sources, like syncing a remote API with a local database.
2. ViewModel Layer - The ViewModel creates and manages a stream of paginated data using the Pager class. This produces PagingData, which is then exposed to the UI through reactive streams like Kotlin Flow or LiveData.
3. UI Layer - This is where the paginated data is displayed to the user. It uses PagingDataAdapter, which is a special RecyclerView adapter that knows how to handle PagingData and show items as they load.