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RecyclerView

  • บทความ

RecyclerView is a view group for displaying collections; it is designed to be a more flexible replacement for older view groups such as ListView and GridView. This guide explains how to use and customize RecyclerView in Xamarin.Android applications.

RecyclerView

Many apps need to display collections of the same type (such as messages, contacts, images, or songs); often, this collection is too large to fit on the screen, so the collection is presented in a small window that can smoothly scroll through all items in the collection. RecyclerView is an Android widget that displays a collection of items in a list or a grid, enabling the user to scroll through the collection. The following is a screenshot of an example app that uses RecyclerView to display email inbox contents in a vertical scrolling list:

Example app using RecyclerView to list inbox messages

RecyclerView offers two compelling features:

  • It has a flexible architecture that lets you modify its behavior by plugging in your preferred components.

  • It is efficient with large collections because it reuses item views and requires the use of view holders to cache view references.

This guide explains how to use RecyclerView in Xamarin.Android applications; it explains how to add the RecyclerView package to your Xamarin.Android project, and it describes how RecyclerView functions in a typical application. Real code examples are provided to show you how to integrate RecyclerView into your application, how to implement item-view click, and how to refresh RecyclerView when its underlying data changes. This guide assumes that you are familiar with Xamarin.Android development.

Requirements

Although RecyclerView is often associated with Android 5.0 Lollipop, it is offered as a support library – RecyclerView works with apps that target API level 7 (Android 2.1) and later. The following is required to use RecyclerView in Xamarin-based applications:

  • Xamarin.Android – Xamarin.Android 4.20 or later must be installed and configured with either Visual Studio or Visual Studio for Mac.

  • Your app project must include the Xamarin.Android.Support.v7.RecyclerView package. For more information about installing NuGet packages, see Walkthrough: Including a NuGet in your project.

Overview

RecyclerView can be thought of as a replacement for the ListView and GridView widgets in Android. Like its predecessors, RecyclerView is designed to display a large data set in a small window, but RecyclerView offers more layout options and is better optimized for displaying large collections. If you are familiar with ListView, there are several important differences between ListView and RecyclerView:

  • RecyclerView is slightly more complex to use: you have to write more code to use RecyclerView compared to ListView.

  • RecyclerView does not provide a predefined adapter; you must implement the adapter code that accesses your data source. However, Android includes several predefined adapters that work with ListView and GridView.

  • RecyclerView does not offer an item-click event when a user taps an item; instead, item-click events are handled by helper classes. By contrast, ListView offers an item-click event.

  • RecyclerView enhances performance by recycling views and by enforcing the view-holder pattern, which eliminates unnecessary layout resource lookups. Use of the view-holder pattern is optional in ListView.

  • RecyclerView is based on a modular design that makes it easier to customize. For example, you can plug in a different layout policy without significant code changes to your app. By contrast, ListView is relatively monolithic in structure.

  • RecyclerView includes built-in animations for item add and remove. ListView animations require some additional effort on the part of the app developer.

Sections

RecyclerView Parts and Functionality

This topic explains how the Adapter, LayoutManager, and ViewHolder work together as helper classes to support RecyclerView. It provides a high-level overview of each of these helper classes and explains how you use them in your app.

A Basic RecyclerView Example

This topic builds on the information provided in RecyclerView Parts and Functionality by providing real code examples of how the various RecyclerView elements are implemented to build a real-world photo-browsing app.

Extending the RecyclerView Example

This topic adds additional code to the example app presented in A Basic RecyclerView Example to demonstrate how to handle item-click events and update RecyclerView when the underlying data source changes.

Summary

This guide introduced the Android RecyclerView widget; it explained how to add the RecyclerView support library to Xamarin.Android projects, how RecyclerView recycles views, how it enforces the view-holder pattern for efficiency, and how the various helper classes that make up RecyclerView collaborate to display collections. It provided example code to demonstrate how RecyclerView is integrated into an application, it explained how to tailor RecyclerView's layout policy by plugging in different layout managers, and it described how to handle item click events and notify RecyclerView of data source changes.

For more information about RecyclerView, see the RecyclerView class reference.