A flexible view for providing a limited window into a large data set.
Glossary of terms:
- Adapter: A subclass of
RecyclerView.Adapterresponsible 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.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.
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
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
null results from these methods.
RecyclerView widget is a more advanced and flexible version of
ListView. This widget is a container for displaying large data sets that can be scrolled very efficiently by maintaining a limited number of views. Use the
RecyclerView widget when you have data collections whose elements change at runtime based on user action or network events.
RecyclerView class simplifies the display and handling of large data sets by providing:
- Layout managers for positioning items
- Default animations for common item operations, such as removal or addition of items
You also have the flexibility to define custom layout managers and animations for
The following code example demonstrates how to add the
RecyclerView to a layout:
<!-- A RecyclerView with some commonly used attributes --> <android.support.v7.widget.RecyclerView android:id="@+id/my_recycler_view" android:scrollbars="vertical" android:layout_width="match_parent" android:layout_height="match_parent"/>