RecyclerView in Android

RecyclerView is a ViewGroup that helps us to display a scrollable list of elements. It is one of the most used UI components in the Android apps and it involves having a data source, an adapter, and the RecyclerView. Other than displaying the content, RecyclerView is efficiently reusing the views that have scrolled off the screen by recycling them.

📃Components Overview

• Data source — list of objects that could be obtained from a local database, or as a result of a http request, or even it could be a list with some predefined values.
• RecyclerView is a scrolling list for list items and to have access at it we must add some dependencies in the gradle file
• Layout for one item of data — XML file
• Layout manager handles the organization of UI components in a view (there are 3 predefined ways to display the items)
• View holder has view information for displaying one item
• Adapter connects data to the RecyclerView
• Set the Adapter to the RecyclerView and we are done 🙂

LayoutManager

Adapter

• We are talking about applying the adapter design pattern as an intermediary between the source data we want to display and the view
• Adapter is a structural design pattern that allows objects with incompatible interfaces to collaborate
• Responsibile to create, updade, add and delete items from the list
• It suppose to implement the abstract class RecyclerView.Adapter

ViewHolder

• Used by the adapter to prepare one item view for each element from the datasource
• The layout of the item is specified in an XML resource file, it’s like a 1:1 relation between the view and the element from the list of objects provided as a datasource
• Can have clickable elements and it is placed by the layout manager
• We must implement the abstract class RecyclerView.ViewHolder

👩🏻‍💻Implementation steps

1. Get the data by creating a new object class (data source)
2. Add the RecyclerView dependency to app/build.gradle file and add RecyclerView to layout
3. Create XML layout for item
4. Define the LayoutManager in activity
5. Extend RecyclerView.ViewHolder in a separated class
6. Extend RecyclerView.Adapter in a separated class
7. In onCreate of activity, create a RecyclerView with adapter and layout manager

To cover the implementation steps we will display a list of emails. The data source is hardcoded, right now we are focusing on learning how to use RecyclerView.

Step 1: Get the data by creating a new object class (data source)

Step 2: Add the RecyclerView dependency to app/build.gradle file and add RecyclerView to layout

Step 3: Create XML layout for item

Step 4: Define the LayoutManager in activity

Step 5: Extend RecyclerView.ViewHolder in a separated class

Step 6: Extend RecyclerView.Adapter in a separated class

Step 7: In onCreate of activity, create a RecyclerView with adapter and layout manager

🔔Notify the Adapter

To not impact the speed of rendering the UI elements for a RecyclerView make sure that you’re not calling notifyDataSetChanged(), setAdapter(Adapter), or swapAdapter(Adapter, boolean) for small updates. [official recommendation] The solution is to use SortedListor DiffUtilto create minimal updates when the data source has changed.

✨Item decorators

We could set dividers between the items using DividerItemDecoration

💫Swipe to refresh

Step 1: Add a new dependency in the gradle file

Step 2: Wrap the RecyclerView in a SwipeRefreshLayout

Step 3: Update the code in the Adapter

Step 4: Setup SwipeRefreshLayout

You could check the full source code here. (different branches for each section)

📚Learn more

• Android Vitals — Slow Rendering
• Create dynamic lists with RecyclerView
• RecyclerView ins and outs — Google I/O 2016
• Yigit Boyar: Pro RecyclerView

Enjoy and feel free to leave a comment if something is not clear or if you have questions. And if you like it please share!

Thank you for reading! 🙂

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Originally published at http://magdamiu.com on December 28, 2020.