RecyclerView

Kotlin |Java

open class RecyclerView : ViewGroup, ScrollingView, NestedScrollingChild2, NestedScrollingChild3

kotlin.Any
↳	android.view.View
	↳	android.view.ViewGroup
		↳	androidx.recyclerview.widget.RecyclerView

Known Direct Subclasses

BaseGridView, WearableRecyclerView

BaseGridView	An abstract base class for vertically and horizontally scrolling lists.
WearableRecyclerView	Wearable specific implementation of the `RecyclerView` enabling circular scrolling} and semi-circular layouts.

Known Indirect Subclasses

HorizontalGridView, VerticalGridView

HorizontalGridView	A `android.view.ViewGroup` that shows items in a horizontal scrolling list.
VerticalGridView	A `android.view.ViewGroup` that shows items in a vertically scrolling list.

A flexible view for providing a limited window into a large data set.

Glossary of terms:

Adapter: A subclass of Adapter responsible for providing views that represent items in a data set.
Position: The position of a data item within an Adapter.
Index: The index of an attached child view as used in a call to ViewGroup#getChildAt. Contrast with Position.
Binding: The process of preparing a child view to display data corresponding to a position within the adapter.
Recycle (view): A view previously used to display data for a specific adapter position may be placed in a cache for later reuse to display the same type of data again later. This can drastically improve performance by skipping initial layout inflation or construction.
Scrap (view): A child view that has entered into a temporarily detached state during layout. Scrap views may be reused without becoming fully detached from the parent RecyclerView, either unmodified if no rebinding is required or modified by the adapter if the view was considered dirty.
Dirty (view): A child view that must be rebound by the adapter before being displayed.

Positions in RecyclerView:

RecyclerView introduces an additional level of abstraction between the Adapter and LayoutManager to be able to detect data set changes in batches during a layout calculation. This saves LayoutManager from tracking adapter changes to calculate animations. It also helps with performance because all view bindings happen at the same time and unnecessary bindings are avoided.

For this reason, there are two types of position related methods in RecyclerView:

layout position: Position of an item in the latest layout calculation. This is the position from the LayoutManager's perspective.
adapter position: Position of an item in the adapter. This is the position from the Adapter's perspective.

These two positions are the same except the time between dispatching adapter.notify* events and calculating the updated layout.

Methods that return or receive *LayoutPosition* use position as of the latest layout calculation (e.g. ViewHolder#getLayoutPosition(), findViewHolderForLayoutPosition(int)). These positions include all changes until the last layout calculation. You can rely on these positions to be consistent with what user is currently seeing on the screen. For example, if you have a list of items on the screen and user asks for the 5th element, you should use these methods as they'll match what user is seeing.

The other set of position related methods are in the form of *AdapterPosition*. (e.g. ViewHolder#getAbsoluteAdapterPosition(), ViewHolder#getBindingAdapterPosition(), findViewHolderForAdapterPosition(int)) You should use these methods when you need to work with up-to-date adapter positions even if they may not have been reflected to layout yet. For example, if you want to access the item in the adapter on a ViewHolder click, you should use ViewHolder#getBindingAdapterPosition(). Beware that these methods may not be able to calculate adapter positions if Adapter#notifyDataSetChanged() has been called and new layout has not yet been calculated. For this reasons, you should carefully handle NO_POSITION or null results from these methods.

When writing a LayoutManager you almost always want to use layout positions whereas when writing an Adapter, you probably want to use adapter positions.

Presenting Dynamic Data

To display updatable data in a RecyclerView, your adapter needs to signal inserts, moves, and deletions to RecyclerView. You can build this yourself by manually calling adapter.notify* methods when content changes, or you can use one of the easier solutions RecyclerView provides:

List diffing with DiffUtil

If your RecyclerView is displaying a list that is re-fetched from scratch for each update (e.g. from the network, or from a database), DiffUtil can calculate the difference between versions of the list. DiffUtil takes both lists as input and computes the difference, which can be passed to RecyclerView to trigger minimal animations and updates to keep your UI performant, and animations meaningful. This approach requires that each list is represented in memory with immutable content, and relies on receiving updates as new instances of lists. This approach is also ideal if your UI layer doesn't implement sorting, it just presents the data in the order it's given.

The best part of this approach is that it extends to any arbitrary changes - item updates, moves, addition and removal can all be computed and handled the same way. Though you do have to keep two copies of the list in memory while diffing, and must avoid mutating them, it's possible to share unmodified elements between list versions.

There are three primary ways to do this for RecyclerView. We recommend you start with ListAdapter, the higher-level API that builds in List diffing on a background thread, with minimal code. AsyncListDiffer also provides this behavior, but without defining an Adapter to subclass. If you want more control, DiffUtil is the lower-level API you can use to compute the diffs yourself. Each approach allows you to specify how diffs should be computed based on item data.

List mutation with SortedList

If your RecyclerView receives updates incrementally, e.g. item X is inserted, or item Y is removed, you can use SortedList to manage your list. You define how to order items, and it will automatically trigger update signals that RecyclerView can use. SortedList works if you only need to handle insert and remove events, and has the benefit that you only ever need to have a single copy of the list in memory. It can also compute differences with SortedList#replaceAll(Object[]), but this method is more limited than the list diffing behavior above.

Paging Library

The Paging library extends the diff-based approach to additionally support paged loading. It provides the androidx.paging.PagedList class that operates as a self-loading list, provided a source of data like a database, or paginated network API. It provides convenient list diffing support out of the box, similar to ListAdapter and AsyncListDiffer. For more information about the Paging library, see the library documentation. androidx.recyclerview.R.attr#layoutManager

Summary

Nested classes
abstract	`Adapter` Base class for an Adapter
abstract	`AdapterDataObserver` Observer base class for watching changes to an `Adapter`.
abstract	`ChildDrawingOrderCallback` A callback interface that can be used to alter the drawing order of RecyclerView children.
open	`EdgeEffectFactory` EdgeEffectFactory lets you customize the over-scroll edge effect for RecyclerViews.
abstract	`ItemAnimator` This class defines the animations that take place on items as changes are made to the adapter.
abstract	`ItemDecoration` An ItemDecoration allows the application to add a special drawing and layout offset to specific item views from the adapter's data set.
abstract	`LayoutManager` A `LayoutManager` is responsible for measuring and positioning item views within a `RecyclerView` as well as determining the policy for when to recycle item views that are no longer visible to the user.
open	`LayoutParams` `LayoutParams` subclass for children of `RecyclerView`.
abstract	`OnChildAttachStateChangeListener` A Listener interface that can be attached to a RecylcerView to get notified whenever a ViewHolder is attached to or detached from RecyclerView.
abstract	`OnFlingListener` This class defines the behavior of fling if the developer wishes to handle it.
abstract	`OnItemTouchListener` An OnItemTouchListener allows the application to intercept touch events in progress at the view hierarchy level of the RecyclerView before those touch events are considered for RecyclerView's own scrolling behavior.
abstract	`OnScrollListener` An OnScrollListener can be added to a RecyclerView to receive messages when a scrolling event has occurred on that RecyclerView.
open	`RecycledViewPool` RecycledViewPool lets you share Views between multiple RecyclerViews.
	`Recycler` A Recycler is responsible for managing scrapped or detached item views for reuse.
abstract	`RecyclerListener` A RecyclerListener can be set on a RecyclerView to receive messages whenever a view is recycled.
open	`SimpleOnItemTouchListener` An implementation of `RecyclerView.OnItemTouchListener` that has empty method bodies and default return values.
abstract	`SmoothScroller` Base class for smooth scrolling.
open	`State` Contains useful information about the current RecyclerView state like target scroll position or view focus.
abstract	`ViewCacheExtension` ViewCacheExtension is a helper class to provide an additional layer of view caching that can be controlled by the developer.
abstract	`ViewHolder` A ViewHolder describes an item view and metadata about its place within the RecyclerView.

Constants
static Int	`HORIZONTAL`
static Int	`INVALID_TYPE`
static Long	`NO_ID`
static Int	`NO_POSITION`
static Int	`SCROLL_STATE_DRAGGING` The RecyclerView is currently being dragged by outside input such as user touch input.
static Int	`SCROLL_STATE_IDLE` The RecyclerView is not currently scrolling.
static Int	`SCROLL_STATE_SETTLING` The RecyclerView is currently animating to a final position while not under outside control.
static Int	`TOUCH_SLOP_DEFAULT` Constant for use with `setScrollingTouchSlop(int)`.
static Int	`TOUCH_SLOP_PAGING` Constant for use with `setScrollingTouchSlop(int)`.
static Int	`UNDEFINED_DURATION` Constant that represents that a duration has not been defined.
static Int	`VERTICAL`

Public constructors
`<init>(@NonNull context: Context)`
`<init>(@NonNull context: Context, @Nullable attrs: AttributeSet?)`
`<init>(@NonNull context: Context, @Nullable attrs: AttributeSet?, defStyleAttr: Int)`

Public methods
open Unit	`addFocusables(views: ArrayList<View!>!, direction: Int, focusableMode: Int)`
open Unit	`addItemDecoration(@NonNull decor: RecyclerView.ItemDecoration, index: Int)` Add an `ItemDecoration` to this RecyclerView.
open Unit	`addItemDecoration(@NonNull decor: RecyclerView.ItemDecoration)` Add an `ItemDecoration` to this RecyclerView.
open Unit	`addOnChildAttachStateChangeListener(@NonNull listener: RecyclerView.OnChildAttachStateChangeListener)` Register a listener that will be notified whenever a child view is attached to or detached from RecyclerView.
open Unit	`addOnItemTouchListener(@NonNull listener: RecyclerView.OnItemTouchListener)` Add an `OnItemTouchListener` to intercept touch events before they are dispatched to child views or this view's standard scrolling behavior.
open Unit	`addOnScrollListener(@NonNull listener: RecyclerView.OnScrollListener)` Add a listener that will be notified of any changes in scroll state or position.
open Unit	`addRecyclerListener(@NonNull listener: RecyclerView.RecyclerListener)` Register a listener that will be notified whenever a child view is recycled.
open Unit	`clearOnChildAttachStateChangeListeners()` Removes all listeners that were added via `addOnChildAttachStateChangeListener(OnChildAttachStateChangeListener)`.
open Unit	`clearOnScrollListeners()` Remove all secondary listener that were notified of any changes in scroll state or position.
open Int	`computeHorizontalScrollExtent()` Compute the horizontal extent of the horizontal scrollbar's thumb within the horizontal range.
open Int	`computeHorizontalScrollOffset()` Compute the horizontal offset of the horizontal scrollbar's thumb within the horizontal range.
open Int	`computeHorizontalScrollRange()` Compute the horizontal range that the horizontal scrollbar represents.
open Int	`computeVerticalScrollExtent()` Compute the vertical extent of the vertical scrollbar's thumb within the vertical range.
open Int	`computeVerticalScrollOffset()` Compute the vertical offset of the vertical scrollbar's thumb within the vertical range.
open Int	`computeVerticalScrollRange()` Compute the vertical range that the vertical scrollbar represents.
open Boolean	`dispatchNestedFling(velocityX: Float, velocityY: Float, consumed: Boolean)`
open Boolean	`dispatchNestedPreFling(velocityX: Float, velocityY: Float)`
open Boolean	`dispatchNestedPreScroll(dx: Int, dy: Int, consumed: IntArray?, offsetInWindow: IntArray?)`
open Boolean	`dispatchNestedPreScroll(dx: Int, dy: Int, consumed: IntArray?, offsetInWindow: IntArray?, type: Int)`
open Boolean	`dispatchNestedScroll(dxConsumed: Int, dyConsumed: Int, dxUnconsumed: Int, dyUnconsumed: Int, offsetInWindow: IntArray?)`
open Boolean	`dispatchNestedScroll(dxConsumed: Int, dyConsumed: Int, dxUnconsumed: Int, dyUnconsumed: Int, offsetInWindow: IntArray?, type: Int)`
Unit	`dispatchNestedScroll(dxConsumed: Int, dyConsumed: Int, dxUnconsumed: Int, dyUnconsumed: Int, offsetInWindow: IntArray?, type: Int, @NonNull consumed: IntArray)`
open Boolean	`dispatchPopulateAccessibilityEvent(event: AccessibilityEvent!)`
open Unit	`draw(c: Canvas!)`
open Boolean	`drawChild(canvas: Canvas!, child: View!, drawingTime: Long)`
open View?	`findChildViewUnder(x: Float, y: Float)` Find the topmost view under the given point.
open View?	`findContainingItemView(@NonNull view: View)` Traverses the ancestors of the given view and returns the item view that contains it and also a direct child of the RecyclerView.
open RecyclerView.ViewHolder?	`findContainingViewHolder(@NonNull view: View)` Returns the ViewHolder that contains the given view.
open RecyclerView.ViewHolder?	`findViewHolderForAdapterPosition(position: Int)` Return the ViewHolder for the item in the given position of the data set.
open RecyclerView.ViewHolder!	`findViewHolderForItemId(id: Long)` Return the ViewHolder for the item with the given id.
open RecyclerView.ViewHolder?	`findViewHolderForLayoutPosition(position: Int)` Return the ViewHolder for the item in the given position of the data set as of the latest layout pass.
open RecyclerView.ViewHolder?	`findViewHolderForPosition(position: Int)`
open Boolean	`fling(velocityX: Int, velocityY: Int)` Begin a standard fling with an initial velocity along each axis in pixels per second.
open View!	`focusSearch(focused: View!, direction: Int)` Since RecyclerView is a collection ViewGroup that includes virtual children (items that are in the Adapter but not visible in the UI), it employs a more involved focus search strategy that differs from other ViewGroups.
open LayoutParams!	`generateLayoutParams(attrs: AttributeSet!)`
open CharSequence!	`getAccessibilityClassName()`
open RecyclerView.Adapter<RecyclerView.ViewHolder!>?	`getAdapter()` Retrieves the previously set adapter or null if no adapter is set.
open Int	`getBaseline()` Return the offset of the RecyclerView's text baseline from the its top boundary.
open Int	`getChildAdapterPosition(@NonNull child: View)` Return the adapter position that the given child view corresponds to.
open Long	`getChildItemId(@NonNull child: View)` Return the stable item id that the given child view corresponds to.
open Int	`getChildLayoutPosition(@NonNull child: View)` Return the adapter position of the given child view as of the latest completed layout pass.
open Int	`getChildPosition(@NonNull child: View)`
open RecyclerView.ViewHolder!	`getChildViewHolder(@NonNull child: View)` Retrieve the `ViewHolder` for the given child view.
open Boolean	`getClipToPadding()` Returns whether this RecyclerView will clip its children to its padding, and resize (but not clip) any EdgeEffect to the padded region, if padding is present.
open RecyclerViewAccessibilityDelegate?	`getCompatAccessibilityDelegate()` Returns the accessibility delegate compatibility implementation used by the RecyclerView.
open Unit	`getDecoratedBoundsWithMargins(@NonNull view: View, @NonNull outBounds: Rect)` Returns the bounds of the view including its decoration and margins.
open RecyclerView.EdgeEffectFactory	`getEdgeEffectFactory()` Retrieves the previously set `EdgeEffectFactory` or the default factory if nothing was set.
open RecyclerView.ItemAnimator?	`getItemAnimator()` Gets the current ItemAnimator for this RecyclerView.
open RecyclerView.ItemDecoration	`getItemDecorationAt(index: Int)` Returns an `ItemDecoration` previously added to this RecyclerView.
open Int	`getItemDecorationCount()` Returns the number of `ItemDecoration` currently added to this RecyclerView.
open RecyclerView.LayoutManager?	`getLayoutManager()` Return the `LayoutManager` currently responsible for layout policy for this RecyclerView.
open Int	`getMaxFlingVelocity()` Returns the maximum fling velocity used by this RecyclerView.
open Int	`getMinFlingVelocity()` Returns the minimum velocity to start a fling.
open RecyclerView.OnFlingListener?	`getOnFlingListener()` Get the current `OnFlingListener` from this `RecyclerView`.
open Boolean	`getPreserveFocusAfterLayout()` Returns true if the RecyclerView should attempt to preserve currently focused Adapter Item's focus even if the View representing the Item is replaced during a layout calculation.
open RecyclerView.RecycledViewPool	`getRecycledViewPool()` Retrieve this RecyclerView's `RecycledViewPool`.
open Int	`getScrollState()` Return the current scrolling state of the RecyclerView.
open Boolean	`hasFixedSize()`
open Boolean	`hasNestedScrollingParent()`
open Boolean	`hasNestedScrollingParent(type: Int)`
open Boolean	`hasPendingAdapterUpdates()` Returns whether there are pending adapter updates which are not yet applied to the layout.
open Unit	`invalidateItemDecorations()` Invalidates all ItemDecorations.
open Boolean	`isAnimating()` Returns true if RecyclerView is currently running some animations.
open Boolean	`isAttachedToWindow()` Returns true if RecyclerView is attached to window.
open Boolean	`isComputingLayout()` Returns whether RecyclerView is currently computing a layout.
open Boolean