RecyclerView

public class RecyclerView
extends ViewGroup implements ScrollingView, NestedScrollingChild2

Known Direct Subclasses BaseGridView,WearableRecyclerView BaseGridView An abstract base class for vertically and horizontally scrolling lists.  WearableRecyclerView Wearable specific implementation of the RecyclerView enabling setCircularScrollingGestureEnabled(boolean) circular scrolling} and semi-circular layouts.

Known Indirect Subclasses HorizontalGridView,VerticalGridView HorizontalGridView A ViewGroup that shows items in a horizontal scrolling list.  VerticalGridView A 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 RecyclerView.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 getChildAt(int). 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 RecyclerView.Adapter and RecyclerView.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. 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 5^th 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. getAdapterPosition(), 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 getAdapterPosition(). Beware that these methods may not be able to calculate adapter positions if 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 RecyclerView.LayoutManager you almost always want to use layout positions whereas when writing an RecyclerView.Adapter, you probably want to use adapter positions.

Summary

Inherited constants
From class android.view.ViewGroup int CLIP_TO_PADDING_MASK int FOCUS_AFTER_DESCENDANTS int FOCUS_BEFORE_DESCENDANTS int FOCUS_BLOCK_DESCENDANTS int LAYOUT_MODE_CLIP_BOUNDS int LAYOUT_MODE_OPTICAL_BOUNDS int PERSISTENT_ALL_CACHES int PERSISTENT_ANIMATION_CACHE int PERSISTENT_NO_CACHE int PERSISTENT_SCROLLING_CACHE
From class android.view.View int ACCESSIBILITY_LIVE_REGION_ASSERTIVE int ACCESSIBILITY_LIVE_REGION_NONE int ACCESSIBILITY_LIVE_REGION_POLITE int AUTOFILL_FLAG_INCLUDE_NOT_IMPORTANT_VIEWS String AUTOFILL_HINT_CREDIT_CARD_EXPIRATION_DATE String AUTOFILL_HINT_CREDIT_CARD_EXPIRATION_DAY String AUTOFILL_HINT_CREDIT_CARD_EXPIRATION_MONTH String AUTOFILL_HINT_CREDIT_CARD_EXPIRATION_YEAR String AUTOFILL_HINT_CREDIT_CARD_NUMBER String AUTOFILL_HINT_CREDIT_CARD_SECURITY_CODE String AUTOFILL_HINT_EMAIL_ADDRESS String AUTOFILL_HINT_NAME String AUTOFILL_HINT_PASSWORD String AUTOFILL_HINT_PHONE String AUTOFILL_HINT_POSTAL_ADDRESS String AUTOFILL_HINT_POSTAL_CODE String AUTOFILL_HINT_USERNAME int AUTOFILL_TYPE_DATE int AUTOFILL_TYPE_LIST int AUTOFILL_TYPE_NONE int AUTOFILL_TYPE_TEXT int AUTOFILL_TYPE_TOGGLE int DRAG_FLAG_GLOBAL int DRAG_FLAG_GLOBAL_PERSISTABLE_URI_PERMISSION int DRAG_FLAG_GLOBAL_PREFIX_URI_PERMISSION int DRAG_FLAG_GLOBAL_URI_READ int DRAG_FLAG_GLOBAL_URI_WRITE int DRAG_FLAG_OPAQUE int DRAWING_CACHE_QUALITY_AUTO int DRAWING_CACHE_QUALITY_HIGH int DRAWING_CACHE_QUALITY_LOW int FIND_VIEWS_WITH_CONTENT_DESCRIPTION int FIND_VIEWS_WITH_TEXT int FOCUSABLE int FOCUSABLES_ALL int FOCUSABLES_TOUCH_MODE int