Android Paging 3.0

Adapting Android: Migrating from Paging 2.0 to Paging 3.0

As part of the Android 11 beta release, Google has also updated the Jetpack Paging library to 3.0, which according to the blog post, is a major update.

..a major update to Paging 3, rewritten Kotlin-first with full support for coroutines!

What’s Changed?

1. A complete rewrite from 2.0 using Kotlin with coroutines.
2. Built-in separator, header and footer support.
3. Built-in retry and refresh mechanism.

Architecture

Despite being a complete rewrite, the architecture remains the same as 2.0.

Figure 1: Paging 3.0 architecture (source)

As comparison, I drafted the common MVVM design pattern that’s been in use for a long while.

Figure 2: Common MVVM design pattern in Android

To map paging 2.0 against Figure 2, we get the following:

• Source -> DataSource
• Pager -> LivePagedListBuilder
• Data Stream -> LiveData<PagedList<T>>
• Adapter -> PagedListAdapter

Migration

With the same architecture, migration is almost a drop-in replacement of a few classes. Let’s visualize the migration as below.

Figure 3: Migration from paging 2.0 to 3.0

Not all classes are required to changed, here’s to summarize:

# Not changed (or required)

• DiffUtil.ItemCallback can be reused as it is.
• DataSource.Factory is no longer required.

# Changed

• Adapter, Config and Pager are all so similar that its almost a straight 1-to-1 mapping.
• ItemKeyedDataSource, PageKeyedDataSource and PositionalDataSource are all merged into a single PagingSource .

Note: PagingSource is backward compatible with LivePagedListBuilder and RxPagedListBuilder if you are using any of this.

Conclusion

• Migration from paging 2.0 to 3.0 seems easy enough.
• Migrating DataSource to PagingSource might required more efforts.
• Not sure if the added features (header, footer, etc) is going to be helpful at this point.

Here is a demo project that implements both paging 2.0 and paging 3.0. You can find a lot of similarities in between the 2 implementations.