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RecyclerView

public class RecyclerView
extends ViewGroup implements ScrollingView, NestedScrollingChild

java.lang.Object
   ↳ android.view.View
     ↳ android.view.ViewGroup
       ↳ android.support.v7.widget.RecyclerView
Known Direct Subclasses


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

Glossary of terms:

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:

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 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. 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

Nested classes

class RecyclerView.Adapter<VH extends RecyclerView.ViewHolder>

Base class for an Adapter

Adapters provide a binding from an app-specific data set to views that are displayed within a RecyclerView

class RecyclerView.AdapterDataObserver

Observer base class for watching changes to an RecyclerView.Adapter

interface RecyclerView.ChildDrawingOrderCallback

A callback interface that can be used to alter the drawing order of RecyclerView children. 

class RecyclerView.ItemAnimator

This class defines the animations that take place on items as changes are made to the adapter. 

class RecyclerView.ItemDecoration

An ItemDecoration allows the application to add a special drawing and layout offset to specific item views from the adapter's data set. 

class RecyclerView.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. 

class RecyclerView.LayoutParams

LayoutParams subclass for children of RecyclerView

interface RecyclerView.OnChildAttachStateChangeListener

A Listener interface that can be attached to a RecylcerView to get notified whenever a ViewHolder is attached to or detached from RecyclerView. 

class RecyclerView.OnFlingListener

This class defines the behavior of fling if the developer wishes to handle it. 

interface RecyclerView.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. 

class RecyclerView.OnScrollListener

An OnScrollListener can be added to a RecyclerView to receive messages when a scrolling event has occurred on that RecyclerView. 

class RecyclerView.RecycledViewPool

RecycledViewPool lets you share Views between multiple RecyclerViews. 

class RecyclerView.Recycler

A Recycler is responsible for managing scrapped or detached item views for reuse. 

interface RecyclerView.RecyclerListener

A RecyclerListener can be set on a RecyclerView to receive messages whenever a view is recycled. 

class RecyclerView.SimpleOnItemTouchListener

An implementation of RecyclerView.OnItemTouchListener that has empty method bodies and default return values. 

class RecyclerView.SmoothScroller

Base class for smooth scrolling. 

class RecyclerView.State

Contains useful information about the current RecyclerView state like target scroll position or view focus. 

class RecyclerView.ViewCacheExtension

ViewCacheExtension is a helper class to provide an additional layer of view caching that can be controlled by the developer. 

class RecyclerView.ViewHolder

A ViewHolder describes an item view and metadata about its place within the RecyclerView. 

XML attributes

android.support.v7.recyclerview:layoutManager Class name of the Layout Manager to be used. 

Inherited XML attributes

From class android.view.ViewGroup
From class android.view.View

Constants

int HORIZONTAL

int INVALID_TYPE

long NO_ID

int NO_POSITION

int SCROLL_STATE_DRAGGING

The RecyclerView is currently being dragged by outside input such as user touch input.

int SCROLL_STATE_IDLE

The RecyclerView is not currently scrolling.

int SCROLL_STATE_SETTLING

The RecyclerView is currently animating to a final position while not under outside control.

int TOUCH_SLOP_DEFAULT

Constant for use with setScrollingTouchSlop(int).

int TOUCH_SLOP_PAGING

Constant for use with setScrollingTouchSlop(int).

int VERTICAL

Inherited constants

From class android.view.ViewGroup
From class android.view.View

Inherited fields

From class android.view.View

Public constructors

RecyclerView(Context context)
RecyclerView(Context context, AttributeSet attrs)
RecyclerView(Context context, AttributeSet attrs, int defStyle)

Public methods

void addFocusables(ArrayList<View> views, int direction, int focusableMode)

Adds any focusable views that are descendants of this view (possibly including this view if it is focusable itself) to views.

void addItemDecoration(RecyclerView.ItemDecoration decor)

Add an RecyclerView.ItemDecoration to this RecyclerView.

void addItemDecoration(RecyclerView.ItemDecoration decor, int index)

Add an RecyclerView.ItemDecoration to this RecyclerView.

void addOnChildAttachStateChangeListener(RecyclerView.OnChildAttachStateChangeListener listener)

Register a listener that will be notified whenever a child view is attached to or detached from RecyclerView.

void addOnItemTouchListener(RecyclerView.OnItemTouchListener listener)

Add an RecyclerView.OnItemTouchListener to intercept touch events before they are dispatched to child views or this view's standard scrolling behavior.

void addOnScrollListener(RecyclerView.OnScrollListener listener)

Add a listener that will be notified of any changes in scroll state or position.

void clearOnChildAttachStateChangeListeners()

Removes all listeners that were added via addOnChildAttachStateChangeListener(OnChildAttachStateChangeListener).

void clearOnScrollListeners()

Remove all secondary listener that were notified of any changes in scroll state or position.

int computeHorizontalScrollExtent()

Compute the horizontal extent of the horizontal scrollbar's thumb within the horizontal range.

int computeHorizontalScrollOffset()

Compute the horizontal offset of the horizontal scrollbar's thumb within the horizontal range.

int computeHorizontalScrollRange()

Compute the horizontal range that the horizontal scrollbar represents.

int computeVerticalScrollExtent()

Compute the vertical extent of the vertical scrollbar's thumb within the vertical range.

int computeVerticalScrollOffset()

Compute the vertical offset of the vertical scrollbar's thumb within the vertical range.

int computeVerticalScrollRange()

Compute the vertical range that the vertical scrollbar represents.

boolean dispatchNestedFling(float velocityX, float velocityY, boolean consumed)

Dispatch a fling to a nested scrolling parent.

boolean dispatchNestedPreFling(float velocityX, float velocityY)

Dispatch a fling to a nested scrolling parent before it is processed by this view.

boolean dispatchNestedPreScroll(int dx, int dy, int[] consumed, int[] offsetInWindow)

Dispatch one step of a nested scroll in progress before this view consumes any portion of it.

boolean dispatchNestedScroll(int dxConsumed, int dyConsumed, int dxUnconsumed, int dyUnconsumed, int[] offsetInWindow)

Dispatch one step of a nested scroll in progress.

void draw(Canvas c)

Manually render this view (and all of its children) to the given Canvas.

boolean drawChild(Canvas canvas, View child, long drawingTime)

Draw one child of this View Group.

View findChildViewUnder(float x, float y)

Find the topmost view under the given point.

View findContainingItemView(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.

RecyclerView.ViewHolder findContainingViewHolder(View view)

Returns the ViewHolder that contains the given view.

RecyclerView.ViewHolder findViewHolderForAdapterPosition(int position)

Return the ViewHolder for the item in the given position of the data set.

RecyclerView.ViewHolder findViewHolderForItemId(long id)

Return the ViewHolder for the item with the given id.

RecyclerView.ViewHolder findViewHolderForLayoutPosition(int position)

Return the ViewHolder for the item in the given position of the data set as of the latest layout pass.

RecyclerView.ViewHolder findViewHolderForPosition(int position)

This method is deprecated. use findViewHolderForLayoutPosition(int) or findViewHolderForAdapterPosition(int)

boolean fling(int velocityX, int velocityY)

Begin a standard fling with an initial velocity along each axis in pixels per second.

View focusSearch(View focused, int direction)

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.

ViewGroup.LayoutParams generateLayoutParams(AttributeSet attrs)

Returns a new set of layout parameters based on the supplied attributes set.

Adapter getAdapter()

Retrieves the previously set adapter or null if no adapter is set.

int getBaseline()

Return the offset of the RecyclerView's text baseline from the its top boundary.

int getChildAdapterPosition(View child)

Return the adapter position that the given child view corresponds to.

long getChildItemId(View child)

Return the stable item id that the given child view corresponds to.

int getChildLayoutPosition(View child)

Return the adapter position of the given child view as of the latest completed layout pass.

int getChildPosition(View child)

This method is deprecated. use getChildAdapterPosition(View) or getChildLayoutPosition(View).

RecyclerView.ViewHolder getChildViewHolder(View child)

Retrieve the RecyclerView.ViewHolder for the given child view.

RecyclerViewAccessibilityDelegate getCompatAccessibilityDelegate()

Returns the accessibility delegate compatibility implementation used by the RecyclerView.

RecyclerView.ItemAnimator getItemAnimator()

Gets the current ItemAnimator for this RecyclerView.

RecyclerView.LayoutManager getLayoutManager()

Return the RecyclerView.LayoutManager currently responsible for layout policy for this RecyclerView.

int getMaxFlingVelocity()

Returns the maximum fling velocity used by this RecyclerView.

int getMinFlingVelocity()

Returns the minimum velocity to start a fling.

RecyclerView.OnFlingListener getOnFlingListener()

Get the current RecyclerView.OnFlingListener from this RecyclerView.

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.

RecyclerView.RecycledViewPool getRecycledViewPool()

Retrieve this RecyclerView's RecyclerView.RecycledViewPool.

int getScrollState()

Return the current scrolling state of the RecyclerView.

boolean hasFixedSize()
boolean hasNestedScrollingParent()

Returns true if this view has a nested scrolling parent.

boolean hasPendingAdapterUpdates()

Returns whether there are pending adapter updates which are not yet applied to the layout.

void invalidateItemDecorations()

Invalidates all ItemDecorations.

boolean isAnimating()

Returns true if RecyclerView is currently running some animations.

boolean isAttachedToWindow()

Returns true if RecyclerView is attached to window.

boolean isComputingLayout()

Returns whether RecyclerView is currently computing a layout.

boolean isLayoutFrozen()

Returns true if layout and scroll are frozen.

boolean isNestedScrollingEnabled()

Returns true if nested scrolling is enabled for this view.

void offsetChildrenHorizontal(int dx)

Offset the bounds of all child views by dx pixels.

void offsetChildrenVertical(int dy)

Offset the bounds of all child views by dy pixels.

void onChildAttachedToWindow(View child)

Called when an item view is attached to this RecyclerView.

void onChildDetachedFromWindow(View child)

Called when an item view is detached from this RecyclerView.

void onDraw(Canvas c)

Implement this to do your drawing.

boolean onGenericMotionEvent(MotionEvent event)

Implement this method to handle generic motion events.

boolean onInterceptTouchEvent(MotionEvent e)

Implement this method to intercept all touch screen motion events.

void onScrollStateChanged(int state)

Called when the scroll state of this RecyclerView changes.

void onScrolled(int dx, int dy)

Called when the scroll position of this RecyclerView changes.

boolean onTouchEvent(MotionEvent e)

Implement this method to handle touch screen motion events.

void removeItemDecoration(RecyclerView.ItemDecoration decor)

Remove an RecyclerView.ItemDecoration from this RecyclerView.

void removeOnChildAttachStateChangeListener(RecyclerView.OnChildAttachStateChangeListener listener)

Removes the provided listener from child attached state listeners list.

void removeOnItemTouchListener(RecyclerView.OnItemTouchListener listener)

Remove an RecyclerView.OnItemTouchListener.

void removeOnScrollListener(RecyclerView.OnScrollListener listener)

Remove a listener that was notified of any changes in scroll state or position.

void requestChildFocus(View child, View focused)

Called when a child of this parent wants focus

boolean requestChildRectangleOnScreen(View child, Rect rect, boolean immediate)

Called when a child of this group wants a particular rectangle to be positioned onto the screen.

void requestDisallowInterceptTouchEvent(boolean disallowIntercept)

Called when a child does not want this parent and its ancestors to intercept touch events with onInterceptTouchEvent(MotionEvent).

void requestLayout()

Call this when something has changed which has invalidated the layout of this view.

void scrollBy(int x, int y)

Move the scrolled position of your view.

void scrollTo(int x, int y)

Set the scrolled position of your view.

void scrollToPosition(int position)

Convenience method to scroll to a certain position.

void sendAccessibilityEventUnchecked(AccessibilityEvent event)

This method behaves exactly as sendAccessibilityEvent(int) but takes as an argument an empty AccessibilityEvent and does not perform a check whether accessibility is enabled.

void setAccessibilityDelegateCompat(RecyclerViewAccessibilityDelegate accessibilityDelegate)

Sets the accessibility delegate compatibility implementation used by RecyclerView.

void setAdapter(Adapter adapter)

Set a new adapter to provide child views on demand.

void setChildDrawingOrderCallback(RecyclerView.ChildDrawingOrderCallback childDrawingOrderCallback)

Sets the RecyclerView.ChildDrawingOrderCallback to be used for drawing children.

void setClipToPadding(boolean clipToPadding)

Sets whether this ViewGroup will clip its children to its padding and resize (but not clip) any EdgeEffect to the padded region, if padding is present.

void setHasFixedSize(boolean hasFixedSize)

RecyclerView can perform several optimizations if it can know in advance that RecyclerView's size is not affected by the adapter contents.

void setItemAnimator(RecyclerView.ItemAnimator animator)

Sets the RecyclerView.ItemAnimator that will handle animations involving changes to the items in this RecyclerView.

void setItemViewCacheSize(int size)

Set the number of offscreen views to retain before adding them to the potentially shared recycled view pool.

void setLayoutFrozen(boolean frozen)

Enable or disable layout and scroll.

void setLayoutManager(RecyclerView.LayoutManager layout)

Set the RecyclerView.LayoutManager that this RecyclerView will use.

void setNestedScrollingEnabled(boolean enabled)

Enable or disable nested scrolling for this view.

void setOnFlingListener(RecyclerView.OnFlingListener onFlingListener)

Set a RecyclerView.OnFlingListener for this RecyclerView.

void setOnScrollListener(RecyclerView.OnScrollListener listener)

This method is deprecated. Use addOnScrollListener(OnScrollListener) and removeOnScrollListener(OnScrollListener)

void setPreserveFocusAfterLayout(boolean preserveFocusAfterLayout)

Set whether the RecyclerView should try to keep the same Item focused after a layout calculation or not.

void setRecycledViewPool(RecyclerView.RecycledViewPool pool)

Recycled view pools allow multiple RecyclerViews to share a common pool of scrap views.

void setRecyclerListener(RecyclerView.RecyclerListener listener)

Register a listener that will be notified whenever a child view is recycled.

void setScrollingTouchSlop(int slopConstant)

Configure the scrolling touch slop for a specific use case.

void setViewCacheExtension(RecyclerView.ViewCacheExtension extension)

Sets a new RecyclerView.ViewCacheExtension to be used by the Recycler.

void smoothScrollBy(int dx, int dy)

Animate a scroll by the given amount of pixels along either axis.

void smoothScrollToPosition(int position)

Starts a smooth scroll to an adapter position.

boolean startNestedScroll(int axes)

Begin a nestable scroll operation along the given axes.

void stopNestedScroll()

Stop a nested scroll in progress.

void stopScroll()

Stop any current scroll in progress, such as one started by smoothScrollBy(int, int), fling(int, int) or a touch-initiated fling.

void swapAdapter(Adapter adapter, boolean removeAndRecycleExistingViews)

Swaps the current adapter with the provided one.

Protected methods

boolean checkLayoutParams(ViewGroup.LayoutParams p)
void dispatchRestoreInstanceState(SparseArray<Parcelable> container)

Override to prevent thawing of any views created by the adapter.

void dispatchSaveInstanceState(SparseArray<Parcelable> container)

Override to prevent freezing of any views created by the adapter.

ViewGroup.LayoutParams generateDefaultLayoutParams()

Returns a set of default layout parameters.

ViewGroup.LayoutParams generateLayoutParams(ViewGroup.LayoutParams p)

Returns a safe set of layout parameters based on the supplied layout params.

int getChildDrawingOrder(int childCount, int i)

Returns the index of the child to draw for this iteration.

void onAttachedToWindow()

This is called when the view is attached to a window.

void onDetachedFromWindow()

This is called when the view is detached from a window.

void onLayout(boolean changed, int l, int t, int r, int b)

Called from layout when this view should assign a size and position to each of its children.

void onMeasure(int widthSpec, int heightSpec)

Measure the view and its content to determine the measured width and the measured height.

boolean onRequestFocusInDescendants(int direction, Rect previouslyFocusedRect)

Look for a descendant to call requestFocus() on.

void onRestoreInstanceState(Parcelable state)

Hook allowing a view to re-apply a representation of its internal state that had previously been generated by onSaveInstanceState().

Parcelable onSaveInstanceState()

Hook allowing a view to generate a representation of its internal state that can later be used to create a new instance with that same state.

void onSizeChanged(int w, int h, int oldw, int oldh)

This is called during layout when the size of this view has changed.

void removeDetachedView(View child, boolean animate)

Finishes the removal of a detached view.

Inherited methods

From class android.view.ViewGroup
From class android.view.View
From class java.lang.Object
From interface android.view.ViewParent
From interface android.view.ViewManager
From interface android.graphics.drawable.Drawable.Callback
From interface android.view.KeyEvent.Callback
From interface android.view.accessibility.AccessibilityEventSource
From interface android.support.v4.view.ScrollingView
From interface android.support.v4.view.NestedScrollingChild

XML attributes

android.support.v7.recyclerview:layoutManager

Class name of the Layout Manager to be used.

The class must extend android.support.v7.widget.RecyclerView$LayoutManager and have either a default constructor or constructor with the signature (android.content.Context, android.util.AttributeSet, int, int).

If the name starts with a '.', application package is prefixed. Else, if the name contains a '.', the classname is assumed to be a full class name. Else, the recycler view package name (android.support.v7.widget) is prefixed.

May be a string value, using '\\;' to escape characters such as '\\n' or '\\uxxxx' for a unicode character;

Constants

HORIZONTAL

int HORIZONTAL

Constant Value: 0 (0x00000000)

INVALID_TYPE

int INVALID_TYPE

Constant Value: -1 (0xffffffff)

NO_ID

long NO_ID

Constant Value: -1 (0xffffffffffffffff)

NO_POSITION

int NO_POSITION

Constant Value: -1 (0xffffffff)

SCROLL_STATE_DRAGGING

int SCROLL_STATE_DRAGGING

The RecyclerView is currently being dragged by outside input such as user touch input.

See also:

Constant Value: 1 (0x00000001)

SCROLL_STATE_IDLE

int SCROLL_STATE_IDLE

The RecyclerView is not currently scrolling.

See also:

Constant Value: 0 (0x00000000)

SCROLL_STATE_SETTLING

int SCROLL_STATE_SETTLING

The RecyclerView is currently animating to a final position while not under outside control.

See also:

Constant Value: 2 (0x00000002)

TOUCH_SLOP_DEFAULT

int TOUCH_SLOP_DEFAULT

Constant for use with setScrollingTouchSlop(int). Indicates that the RecyclerView should use the standard touch slop for smooth, continuous scrolling.

Constant Value: 0 (0x00000000)

TOUCH_SLOP_PAGING

int TOUCH_SLOP_PAGING

Constant for use with setScrollingTouchSlop(int). Indicates that the RecyclerView should use the standard touch slop for scrolling widgets that snap to a page or other coarse-grained barrier.

Constant Value: 1 (0x00000001)

VERTICAL

int VERTICAL

Constant Value: 1 (0x00000001)

Public constructors

RecyclerView

RecyclerView (Context context)

Parameters
context Context

RecyclerView

RecyclerView (Context context, 
                AttributeSet attrs)

Parameters
context Context
attrs AttributeSet

RecyclerView

RecyclerView (Context context, 
                AttributeSet attrs, 
                int defStyle)

Parameters
context Context
attrs AttributeSet
defStyle int

Public methods

addFocusables

void addFocusables (ArrayList<View> views, 
                int direction, 
                int focusableMode)

Adds any focusable views that are descendants of this view (possibly including this view if it is focusable itself) to views. This method adds all focusable views regardless if we are in touch mode or only views focusable in touch mode if we are in touch mode or only views that can take accessibility focus if accessibility is enabled depending on the focusable mode parameter.

Parameters
views ArrayList: Focusable views found so far or null if all we are interested is the number of focusables.
direction int: The direction of the focus.
focusableMode int: The type of focusables to be added.

addItemDecoration

void addItemDecoration (RecyclerView.ItemDecoration decor)

Add an RecyclerView.ItemDecoration to this RecyclerView. Item decorations can affect both measurement and drawing of individual item views.

Item decorations are ordered. Decorations placed earlier in the list will be run/queried/drawn first for their effects on item views. Padding added to views will be nested; a padding added by an earlier decoration will mean further item decorations in the list will be asked to draw/pad within the previous decoration's given area.

Parameters
decor RecyclerView.ItemDecoration: Decoration to add

addItemDecoration

void addItemDecoration (RecyclerView.ItemDecoration decor, 
                int index)

Add an RecyclerView.ItemDecoration to this RecyclerView. Item decorations can affect both measurement and drawing of individual item views.

Item decorations are ordered. Decorations placed earlier in the list will be run/queried/drawn first for their effects on item views. Padding added to views will be nested; a padding added by an earlier decoration will mean further item decorations in the list will be asked to draw/pad within the previous decoration's given area.

Parameters
decor RecyclerView.ItemDecoration: Decoration to add
index int: Position in the decoration chain to insert this decoration at. If this value is negative the decoration will be added at the end.

addOnChildAttachStateChangeListener

void addOnChildAttachStateChangeListener (RecyclerView.OnChildAttachStateChangeListener listener)

Register a listener that will be notified whenever a child view is attached to or detached from RecyclerView.

This listener will be called when a LayoutManager or the RecyclerView decides that a child view is no longer needed. If an application associates expensive or heavyweight data with item views, this may be a good place to release or free those resources.

Parameters
listener RecyclerView.OnChildAttachStateChangeListener: Listener to register

addOnItemTouchListener

void addOnItemTouchListener (RecyclerView.OnItemTouchListener listener)

Add an RecyclerView.OnItemTouchListener to intercept touch events before they are dispatched to child views or this view's standard scrolling behavior.

Client code may use listeners to implement item manipulation behavior. Once a listener returns true from onInterceptTouchEvent(RecyclerView, MotionEvent) its onTouchEvent(RecyclerView, MotionEvent) method will be called for each incoming MotionEvent until the end of the gesture.

Parameters
listener RecyclerView.OnItemTouchListener: Listener to add

See also:

addOnScrollListener

void addOnScrollListener (RecyclerView.OnScrollListener listener)

Add a listener that will be notified of any changes in scroll state or position.

Components that add a listener should take care to remove it when finished. Other components that take ownership of a view may call clearOnScrollListeners() to remove all attached listeners.

Parameters
listener RecyclerView.OnScrollListener: listener to set or null to clear

clearOnChildAttachStateChangeListeners

void clearOnChildAttachStateChangeListeners ()

Removes all listeners that were added via addOnChildAttachStateChangeListener(OnChildAttachStateChangeListener).

clearOnScrollListeners

void clearOnScrollListeners ()

Remove all secondary listener that were notified of any changes in scroll state or position.

computeHorizontalScrollExtent

int computeHorizontalScrollExtent ()

Compute the horizontal extent of the horizontal scrollbar's thumb within the horizontal range. This value is used to compute the length of the thumb within the scrollbar's track.

The range is expressed in arbitrary units that must be the same as the units used by computeHorizontalScrollRange() and computeHorizontalScrollOffset().

Default implementation returns 0.

If you want to support scroll bars, override computeHorizontalScrollExtent(RecyclerView.State) in your LayoutManager.

Returns
int The horizontal extent of the scrollbar's thumb

See also:

computeHorizontalScrollOffset

int computeHorizontalScrollOffset ()

Compute the horizontal offset of the horizontal scrollbar's thumb within the horizontal range. This value is used to compute the length of the thumb within the scrollbar's track.

The range is expressed in arbitrary units that must be the same as the units used by computeHorizontalScrollRange() and computeHorizontalScrollExtent().

Default implementation returns 0.

If you want to support scroll bars, override computeHorizontalScrollOffset(RecyclerView.State) in your LayoutManager.

Returns
int The horizontal offset of the scrollbar's thumb

See also:

computeHorizontalScrollRange

int computeHorizontalScrollRange ()

Compute the horizontal range that the horizontal scrollbar represents.

The range is expressed in arbitrary units that must be the same as the units used by computeHorizontalScrollExtent() and computeHorizontalScrollOffset().

Default implementation returns 0.

If you want to support scroll bars, override computeHorizontalScrollRange(RecyclerView.State) in your LayoutManager.

Returns
int The total horizontal range represented by the vertical scrollbar

See also:

computeVerticalScrollExtent

int computeVerticalScrollExtent ()

Compute the vertical extent of the vertical scrollbar's thumb within the vertical range. This value is used to compute the length of the thumb within the scrollbar's track.

The range is expressed in arbitrary units that must be the same as the units used by computeVerticalScrollRange() and computeVerticalScrollOffset().

Default implementation returns 0.

If you want to support scroll bars, override computeVerticalScrollExtent(RecyclerView.State) in your LayoutManager.

Returns
int The vertical extent of the scrollbar's thumb

See also:

computeVerticalScrollOffset

int computeVerticalScrollOffset ()

Compute the vertical offset of the vertical scrollbar's thumb within the vertical range. This value is used to compute the length of the thumb within the scrollbar's track.

The range is expressed in arbitrary units that must be the same as the units used by computeVerticalScrollRange() and computeVerticalScrollExtent().

Default implementation returns 0.

If you want to support scroll bars, override computeVerticalScrollOffset(RecyclerView.State) in your LayoutManager.

Returns
int The vertical offset of the scrollbar's thumb

See also:

computeVerticalScrollRange

int computeVerticalScrollRange ()

Compute the vertical range that the vertical scrollbar represents.

The range is expressed in arbitrary units that must be the same as the units used by computeVerticalScrollExtent() and computeVerticalScrollOffset().

Default implementation returns 0.

If you want to support scroll bars, override computeVerticalScrollRange(RecyclerView.State) in your LayoutManager.

Returns
int The total vertical range represented by the vertical scrollbar

See also:

dispatchNestedFling

boolean dispatchNestedFling (float velocityX, 
                float velocityY, 
                boolean consumed)

Dispatch a fling to a nested scrolling parent.

This method should be used to indicate that a nested scrolling child has detected suitable conditions for a fling. Generally this means that a touch scroll has ended with a velocity in the direction of scrolling that meets or exceeds the minimum fling velocity along a scrollable axis.

If a nested scrolling child view would normally fling but it is at the edge of its own content, it can use this method to delegate the fling to its nested scrolling parent instead. The parent may optionally consume the fling or observe a child fling.

Parameters
velocityX float: Horizontal fling velocity in pixels per second
velocityY float: Vertical fling velocity in pixels per second
consumed boolean: true if the child consumed the fling, false otherwise
Returns
boolean true if the nested scrolling parent consumed or otherwise reacted to the fling

dispatchNestedPreFling

boolean dispatchNestedPreFling (float velocityX, 
                float velocityY)

Dispatch a fling to a nested scrolling parent before it is processed by this view.

Nested pre-fling events are to nested fling events what touch intercept is to touch and what nested pre-scroll is to nested scroll. dispatchNestedPreFling offsets an opportunity for the parent view in a nested fling to fully consume the fling before the child view consumes it. If this method returns true, a nested parent view consumed the fling and this view should not scroll as a result.

For a better user experience, only one view in a nested scrolling chain should consume the fling at a time. If a parent view consumed the fling this method will return false. Custom view implementations should account for this in two ways:

  • If a custom view is paged and needs to settle to a fixed page-point, do not call dispatchNestedPreFling; consume the fling and settle to a valid position regardless.
  • If a nested parent does consume the fling, this view should not scroll at all, even to settle back to a valid idle position.

Views should also not offer fling velocities to nested parent views along an axis where scrolling is not currently supported; a ScrollView should not offer a horizontal fling velocity to its parents since scrolling along that axis is not permitted and carrying velocity along that motion does not make sense.

Parameters
velocityX float: Horizontal fling velocity in pixels per second
velocityY float: Vertical fling velocity in pixels per second
Returns
boolean true if a nested scrolling parent consumed the fling

dispatchNestedPreScroll

boolean dispatchNestedPreScroll (int dx, 
                int dy, 
                int[] consumed, 
                int[] offsetInWindow)

Dispatch one step of a nested scroll in progress before this view consumes any portion of it.

Nested pre-scroll events are to nested scroll events what touch intercept is to touch. dispatchNestedPreScroll offers an opportunity for the parent view in a nested scrolling operation to consume some or all of the scroll operation before the child view consumes it.

Parameters
dx int: Horizontal scroll distance in pixels
dy int: Vertical scroll distance in pixels
consumed int: Output. If not null, consumed[0] will contain the consumed component of dx and consumed[1] the consumed dy.
offsetInWindow int: Optional. If not null, on return this will contain the offset in local view coordinates of this view from before this operation to after it completes. View implementations may use this to adjust expected input coordinate tracking.
Returns
boolean true if the parent consumed some or all of the scroll delta

dispatchNestedScroll

boolean dispatchNestedScroll (int dxConsumed, 
                int dyConsumed, 
                int dxUnconsumed, 
                int dyUnconsumed, 
                int[] offsetInWindow)

Dispatch one step of a nested scroll in progress.

Implementations of views that support nested scrolling should call this to report info about a scroll in progress to the current nested scrolling parent. If a nested scroll is not currently in progress or nested scrolling is not enabled for this view this method does nothing.

Compatible View implementations should also call dispatchNestedPreScroll before consuming a component of the scroll event themselves.

Parameters
dxConsumed int: Horizontal distance in pixels consumed by this view during this scroll step
dyConsumed int: Vertical distance in pixels consumed by this view during this scroll step
dxUnconsumed int: Horizontal scroll distance in pixels not consumed by this view
dyUnconsumed int: Horizontal scroll distance in pixels not consumed by this view
offsetInWindow int: Optional. If not null, on return this will contain the offset in local view coordinates of this view from before this operation to after it completes. View implementations may use this to adjust expected input coordinate tracking.
Returns
boolean true if the event was dispatched, false if it could not be dispatched.

draw

void draw (Canvas c)

Manually render this view (and all of its children) to the given Canvas. The view must have already done a full layout before this function is called. When implementing a view, implement onDraw(android.graphics.Canvas) instead of overriding this method. If you do need to override this method, call the superclass version.

Parameters
c Canvas: The Canvas to which the View is rendered.

drawChild

boolean drawChild (Canvas canvas, 
                View child, 
                long drawingTime)

Draw one child of this View Group. This method is responsible for getting the canvas in the right state. This includes clipping, translating so that the child's scrolled origin is at 0, 0, and applying any animation transformations.

Parameters
canvas Canvas: The canvas on which to draw the child
child View: Who to draw
drawingTime long: The time at which draw is occurring
Returns
boolean True if an invalidate() was issued

findChildViewUnder

View findChildViewUnder (float x, 
                float y)

Find the topmost view under the given point.

Parameters
x float: Horizontal position in pixels to search
y float: Vertical position in pixels to search
Returns
View The child view under (x, y) or null if no matching child is found

findContainingItemView

View findContainingItemView (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. This returned view can be used to get the ViewHolder by calling getChildViewHolder(View).

Parameters
view View: The view that is a descendant of the RecyclerView.
Returns
View The direct child of the RecyclerView which contains the given view or null if the provided view is not a descendant of this RecyclerView.

See also:

findContainingViewHolder

RecyclerView.ViewHolder findContainingViewHolder (View view)

Returns the ViewHolder that contains the given view.

Parameters
view View: The view that is a descendant of the RecyclerView.
Returns
RecyclerView.ViewHolder The ViewHolder that contains the given view or null if the provided view is not a descendant of this RecyclerView.

findViewHolderForAdapterPosition

RecyclerView.ViewHolder findViewHolderForAdapterPosition (int position)

Return the ViewHolder for the item in the given position of the data set. Unlike findViewHolderForLayoutPosition(int) this method takes into account any pending adapter changes that may not be reflected to the layout yet. On the other hand, if notifyDataSetChanged() has been called but the new layout has not been calculated yet, this method will return null since the new positions of views are unknown until the layout is calculated.

This method checks only the children of RecyclerView. If the item at the given position is not laid out, it will not create a new one.

When the ItemAnimator is running a change animation, there might be 2 ViewHolders representing the same Item. In this case, the updated ViewHolder will be returned.

Parameters
position int: The position of the item in the data set of the adapter
Returns
RecyclerView.ViewHolder The ViewHolder at position or null if there is no such item

findViewHolderForItemId

RecyclerView.ViewHolder findViewHolderForItemId (long id)

Return the ViewHolder for the item with the given id. The RecyclerView must use an Adapter with stableIds to return a non-null value.

This method checks only the children of RecyclerView. If the item with the given id is not laid out, it will not create a new one. When the ItemAnimator is running a change animation, there might be 2 ViewHolders with the same id. In this case, the updated ViewHolder will be returned.

Parameters
id long: The id for the requested item
Returns
RecyclerView.ViewHolder The ViewHolder with the given id or null if there is no such item

findViewHolderForLayoutPosition

RecyclerView.ViewHolder findViewHolderForLayoutPosition (int position)

Return the ViewHolder for the item in the given position of the data set as of the latest layout pass.

This method checks only the children of RecyclerView. If the item at the given position is not laid out, it will not create a new one.

Note that when Adapter contents change, ViewHolder positions are not updated until the next layout calculation. If there are pending adapter updates, the return value of this method may not match your adapter contents. You can use #getAdapterPosition() to get the current adapter position of a ViewHolder.

When the ItemAnimator is running a change animation, there might be 2 ViewHolders with the same layout position representing the same Item. In this case, the updated ViewHolder will be returned.

Parameters
position int: The position of the item in the data set of the adapter
Returns
RecyclerView.ViewHolder The ViewHolder at position or null if there is no such item

findViewHolderForPosition

RecyclerView.ViewHolder findViewHolderForPosition (int position)

This method is deprecated.
use findViewHolderForLayoutPosition(int) or findViewHolderForAdapterPosition(int)

Parameters
position int
Returns
RecyclerView.ViewHolder

fling

boolean fling (int velocityX, 
                int velocityY)

Begin a standard fling with an initial velocity along each axis in pixels per second. If the velocity given is below the system-defined minimum this method will return false and no fling will occur.

Parameters
velocityX int: Initial horizontal velocity in pixels per second
velocityY int: Initial vertical velocity in pixels per second
Returns
boolean true if the fling was started, false if the velocity was too low to fling or LayoutManager does not support scrolling in the axis fling is issued.

See also:

focusSearch

View focusSearch (View focused, 
                int direction)

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.

It first does a focus search within the RecyclerView. If this search finds a View that is in the focus direction with respect to the currently focused View, RecyclerView returns that child as the next focus target. When it cannot find such child, it calls onFocusSearchFailed(View, int, Recycler, State) to layout more Views in the focus search direction. If LayoutManager adds a View that matches the focus search criteria, it will be returned as the focus search result. Otherwise, RecyclerView will call parent to handle the focus search like a regular ViewGroup.

When the direction is FOCUS_FORWARD or FOCUS_BACKWARD, a View that is not in the focus direction is still valid focus target which may not be the desired behavior if the Adapter has more children in the focus direction. To handle this case, RecyclerView converts the focus direction to an absolute direction and makes a preliminary focus search in that direction. If there are no Views to gain focus, it will call onFocusSearchFailed(View, int, Recycler, State) before running a focus search with the original (relative) direction. This allows RecyclerView to provide better candidates to the focus search while still allowing the view system to take focus from the RecyclerView and give it to a more suitable child if such child exists.

Parameters
focused View: The view that currently has focus
direction int: One of FOCUS_UP, FOCUS_DOWN, FOCUS_LEFT, FOCUS_RIGHT, FOCUS_FORWARD, FOCUS_BACKWARD or 0 for not applicable.
Returns
View A new View that can be the next focus after the focused View

generateLayoutParams

ViewGroup.LayoutParams generateLayoutParams (AttributeSet attrs)

Returns a new set of layout parameters based on the supplied attributes set.

Parameters
attrs AttributeSet: the attributes to build the layout parameters from
Returns
ViewGroup.LayoutParams an instance of ViewGroup.LayoutParams or one of its descendants

getAdapter

Adapter getAdapter ()

Retrieves the previously set adapter or null if no adapter is set.

Returns
Adapter The previously set adapter

See also:

getBaseline

int getBaseline ()

Return the offset of the RecyclerView's text baseline from the its top boundary. If the LayoutManager of this RecyclerView does not support baseline alignment, this method returns -1.

Returns
int the offset of the baseline within the RecyclerView's bounds or -1 if baseline alignment is not supported

getChildAdapterPosition

int getChildAdapterPosition (View child)

Return the adapter position that the given child view corresponds to.

Parameters
child View: Child View to query
Returns
int Adapter position corresponding to the given view or NO_POSITION

getChildItemId

long getChildItemId (View child)

Return the stable item id that the given child view corresponds to.

Parameters
child View: Child View to query
Returns
long Item id corresponding to the given view or NO_ID

getChildLayoutPosition

int getChildLayoutPosition (View child)

Return the adapter position of the given child view as of the latest completed layout pass.

This position may not be equal to Item's adapter position if there are pending changes in the adapter which have not been reflected to the layout yet.

Parameters
child View: Child View to query
Returns
int Adapter position of the given View as of last layout pass or NO_POSITION if the View is representing a removed item.

getChildPosition

int getChildPosition (View child)

This method is deprecated.
use getChildAdapterPosition(View) or getChildLayoutPosition(View).

Parameters
child View
Returns
int

getChildViewHolder

RecyclerView.ViewHolder getChildViewHolder (View child)

Retrieve the RecyclerView.ViewHolder for the given child view.

Parameters
child View: Child of this RecyclerView to query for its ViewHolder
Returns
RecyclerView.ViewHolder The child view's ViewHolder

getCompatAccessibilityDelegate

RecyclerViewAccessibilityDelegate getCompatAccessibilityDelegate ()

Returns the accessibility delegate compatibility implementation used by the RecyclerView.

Returns
RecyclerViewAccessibilityDelegate An instance of AccessibilityDelegateCompat used by RecyclerView

getItemAnimator

RecyclerView.ItemAnimator getItemAnimator ()

Gets the current ItemAnimator for this RecyclerView. A null return value indicates that there is no animator and that item changes will happen without any animations. By default, RecyclerView instantiates and uses an instance of DefaultItemAnimator.

Returns
RecyclerView.ItemAnimator ItemAnimator The current ItemAnimator. If null, no animations will occur when changes occur to the items in this RecyclerView.

getLayoutManager

RecyclerView.LayoutManager getLayoutManager ()

Return the RecyclerView.LayoutManager currently responsible for layout policy for this RecyclerView.

Returns
RecyclerView.LayoutManager The currently bound LayoutManager

getMaxFlingVelocity

int getMaxFlingVelocity ()

Returns the maximum fling velocity used by this RecyclerView.

Returns
int The maximum fling velocity used by this RecyclerView.

getMinFlingVelocity

int getMinFlingVelocity ()

Returns the minimum velocity to start a fling.

Returns
int The minimum velocity to start a fling

getOnFlingListener

RecyclerView.OnFlingListener getOnFlingListener ()

Get the current RecyclerView.OnFlingListener from this RecyclerView.

Returns
RecyclerView.OnFlingListener The RecyclerView.OnFlingListener instance currently set (can be null).

getPreserveFocusAfterLayout

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.

By default, this value is true.

Returns
boolean True if the RecyclerView will try to preserve focused Item after a layout if it loses focus.

See also:

getRecycledViewPool

RecyclerView.RecycledViewPool getRecycledViewPool ()

Retrieve this RecyclerView's RecyclerView.RecycledViewPool. This method will never return null; if no pool is set for this view a new one will be created. See setRecycledViewPool for more information.

Returns
RecyclerView.RecycledViewPool The pool used to store recycled item views for reuse.

See also:

getScrollState

int getScrollState ()

Return the current scrolling state of the RecyclerView.

Returns
int SCROLL_STATE_IDLE, SCROLL_STATE_DRAGGING or SCROLL_STATE_SETTLING

hasFixedSize

boolean hasFixedSize ()

Returns
boolean true if the app has specified that changes in adapter content cannot change the size of the RecyclerView itself.

hasNestedScrollingParent

boolean hasNestedScrollingParent ()

Returns true if this view has a nested scrolling parent.

The presence of a nested scrolling parent indicates that this view has initiated a nested scroll and it was accepted by an ancestor view further up the view hierarchy.

Returns
boolean whether this view has a nested scrolling parent

hasPendingAdapterUpdates

boolean hasPendingAdapterUpdates ()

Returns whether there are pending adapter updates which are not yet applied to the layout.

If this method returns true, it means that what user is currently seeing may not reflect them adapter contents (depending on what has changed). You may use this information to defer or cancel some operations.

This method returns true if RecyclerView has not yet calculated the first layout after it is attached to the Window or the Adapter has been replaced.

Returns
boolean True if there are some adapter updates which are not yet reflected to layout or false if layout is up to date.

invalidateItemDecorations

void invalidateItemDecorations ()

Invalidates all ItemDecorations. If RecyclerView has item decorations, calling this method will trigger a requestLayout() call.

isAnimating

boolean isAnimating ()

Returns true if RecyclerView is currently running some animations.

If you want to be notified when animations are finished, use isRunning(ItemAnimator.ItemAnimatorFinishedListener).

Returns
boolean True if there are some item animations currently running or waiting to be started.

isAttachedToWindow

boolean isAttachedToWindow ()

Returns true if RecyclerView is attached to window.

Returns
boolean

isComputingLayout

boolean isComputingLayout ()

Returns whether RecyclerView is currently computing a layout.

If this method returns true, it means that RecyclerView is in a lockdown state and any attempt to update adapter contents will result in an exception because adapter contents cannot be changed while RecyclerView is trying to compute the layout.

It is very unlikely that your code will be running during this state as it is called by the framework when a layout traversal happens or RecyclerView starts to scroll in response to system events (touch, accessibility etc).

This case may happen if you have some custom logic to change adapter contents in response to a View callback (e.g. focus change callback) which might be triggered during a layout calculation. In these cases, you should just postpone the change using a Handler or a similar mechanism.

Returns
boolean true if RecyclerView is currently computing a layout, false otherwise

isLayoutFrozen

boolean isLayoutFrozen ()

Returns true if layout and scroll are frozen.

Returns
boolean true if layout and scroll are frozen

See also:

isNestedScrollingEnabled

boolean isNestedScrollingEnabled ()

Returns true if nested scrolling is enabled for this view.

If nested scrolling is enabled and this View class implementation supports it, this view will act as a nested scrolling child view when applicable, forwarding data about the scroll operation in progress to a compatible and cooperating nested scrolling parent.

Returns
boolean true if nested scrolling is enabled

offsetChildrenHorizontal

void offsetChildrenHorizontal (int dx)

Offset the bounds of all child views by dx pixels. Useful for implementing simple scrolling in LayoutManagers.

Parameters
dx int: Horizontal pixel offset to apply to the bounds of all child views

offsetChildrenVertical

void offsetChildrenVertical (int dy)

Offset the bounds of all child views by dy pixels. Useful for implementing simple scrolling in LayoutManagers.

Parameters
dy int: Vertical pixel offset to apply to the bounds of all child views

onChildAttachedToWindow

void onChildAttachedToWindow (View child)

Called when an item view is attached to this RecyclerView.

Subclasses of RecyclerView may want to perform extra bookkeeping or modifications of child views as they become attached. This will be called before a RecyclerView.LayoutManager measures or lays out the view and is a good time to perform these changes.

Parameters
child View: Child view that is now attached to this RecyclerView and its associated window

onChildDetachedFromWindow

void onChildDetachedFromWindow (View child)

Called when an item view is detached from this RecyclerView.

Subclasses of RecyclerView may want to perform extra bookkeeping or modifications of child views as they become detached. This will be called as a RecyclerView.LayoutManager fully detaches the child view from the parent and its window.

Parameters
child View: Child view that is now detached from this RecyclerView and its associated window

onDraw

void onDraw (Canvas c)

Implement this to do your drawing.

Parameters
c Canvas: the canvas on which the background will be drawn

onGenericMotionEvent

boolean onGenericMotionEvent (MotionEvent event)

Implement this method to handle generic motion events.

Generic motion events describe joystick movements, mouse hovers, track pad touches, scroll wheel movements and other input events. The source of the motion event specifies the class of input that was received. Implementations of this method must examine the bits in the source before processing the event. The following code example shows how this is done.

Generic motion events with source class SOURCE_CLASS_POINTER are delivered to the view under the pointer. All other generic motion events are delivered to the focused view.

 public boolean onGenericMotionEvent(MotionEvent event) {
     if (event.isFromSource(InputDevice.SOURCE_CLASS_JOYSTICK)) {
         if (event.getAction() == MotionEvent.ACTION_MOVE) {
             // process the joystick movement...
             return true;
         }
     }
     if (event.isFromSource(InputDevice.SOURCE_CLASS_POINTER)) {
         switch (event.getAction()) {
             case MotionEvent.ACTION_HOVER_MOVE:
                 // process the mouse hover movement...
                 return true;
             case MotionEvent.ACTION_SCROLL:
                 // process the scroll wheel movement...
                 return true;
         }
     }
     return super.onGenericMotionEvent(event);
 }

Parameters
event MotionEvent: The generic motion event being processed.
Returns
boolean True if the event was handled, false otherwise.

onInterceptTouchEvent

boolean onInterceptTouchEvent (MotionEvent e)

Implement this method to intercept all touch screen motion events. This allows you to watch events as they are dispatched to your children, and take ownership of the current gesture at any point.

Using this function takes some care, as it has a fairly complicated interaction with View.onTouchEvent(MotionEvent), and using it requires implementing that method as well as this one in the correct way. Events will be received in the following order:

  1. You will receive the down event here.
  2. The down event will be handled either by a child of this view group, or given to your own onTouchEvent() method to handle; this means you should implement onTouchEvent() to return true, so you will continue to see the rest of the gesture (instead of looking for a parent view to handle it). Also, by returning true from onTouchEvent(), you will not receive any following events in onInterceptTouchEvent() and all touch processing must happen in onTouchEvent() like normal.
  3. For as long as you return false from this function, each following event (up to and including the final up) will be delivered first here and then to the target's onTouchEvent().
  4. If you return true from here, you will not receive any following events: the target view will receive the same event but with the action ACTION_CANCEL, and all further events will be delivered to your onTouchEvent() method and no longer appear here.

Parameters
e MotionEvent: The motion event being dispatched down the hierarchy.
Returns
boolean Return true to steal motion events from the children and have them dispatched to this ViewGroup through onTouchEvent(). The current target will receive an ACTION_CANCEL event, and no further messages will be delivered here.

onScrollStateChanged

void onScrollStateChanged (int state)

Called when the scroll state of this RecyclerView changes. Subclasses should use this method to respond to state changes instead of an explicit listener.

This method will always be invoked before listeners, but after the LayoutManager responds to the scroll state change.

Parameters
state int: the new scroll state, one of SCROLL_STATE_IDLE, SCROLL_STATE_DRAGGING or SCROLL_STATE_SETTLING

onScrolled

void onScrolled (int dx, 
                int dy)

Called when the scroll position of this RecyclerView changes. Subclasses should use this method to respond to scrolling within the adapter's data set instead of an explicit listener.

This method will always be invoked before listeners. If a subclass needs to perform any additional upkeep or bookkeeping after scrolling but before listeners run, this is a good place to do so.

This differs from onScrollChanged(int, int, int, int) in that it receives the distance scrolled in either direction within the adapter's data set instead of absolute scroll coordinates. Since RecyclerView cannot compute the absolute scroll position from any arbitrary point in the data set, onScrollChanged will always receive the current getScrollX() and getScrollY() values which do not correspond to the data set scroll position. However, some subclasses may choose to use these fields as special offsets.

Parameters
dx int: horizontal distance scrolled in pixels
dy int: vertical distance scrolled in pixels

onTouchEvent

boolean onTouchEvent (MotionEvent e)

Implement this method to handle touch screen motion events.

If this method is used to detect click actions, it is recommended that the actions be performed by implementing and calling performClick(). This will ensure consistent system behavior, including:

  • obeying click sound preferences
  • dispatching OnClickListener calls
  • handling ACTION_CLICK when accessibility features are enabled

Parameters
e MotionEvent: The motion event.
Returns
boolean True if the event was handled, false otherwise.

removeItemDecoration

void removeItemDecoration (RecyclerView.ItemDecoration decor)

Remove an RecyclerView.ItemDecoration from this RecyclerView.

The given decoration will no longer impact the measurement and drawing of item views.

Parameters
decor RecyclerView.ItemDecoration: Decoration to remove

See also:

removeOnChildAttachStateChangeListener

void removeOnChildAttachStateChangeListener (RecyclerView.OnChildAttachStateChangeListener listener)

Removes the provided listener from child attached state listeners list.

Parameters
listener RecyclerView.OnChildAttachStateChangeListener: Listener to unregister

removeOnItemTouchListener

void removeOnItemTouchListener (RecyclerView.OnItemTouchListener listener)

Remove an RecyclerView.OnItemTouchListener. It will no longer be able to intercept touch events.

Parameters
listener RecyclerView.OnItemTouchListener: Listener to remove

removeOnScrollListener

void removeOnScrollListener (RecyclerView.OnScrollListener listener)

Remove a listener that was notified of any changes in scroll state or position.

Parameters
listener RecyclerView.OnScrollListener: listener to set or null to clear

requestChildFocus

void requestChildFocus (View child, 
                View focused)

Called when a child of this parent wants focus

Parameters
child View: The child of this ViewParent that wants focus. This view will contain the focused view. It is not necessarily the view that actually has focus.
focused View: The view that is a descendant of child that actually has focus

requestChildRectangleOnScreen

boolean requestChildRectangleOnScreen (View child, 
                Rect rect, 
                boolean immediate)

Called when a child of this group wants a particular rectangle to be positioned onto the screen. ViewGroups overriding this can trust that:

  • child will be a direct child of this group
  • rectangle will be in the child's content coordinates

ViewGroups overriding this should uphold the contract:

  • nothing will change if the rectangle is already visible
  • the view port will be scrolled only just enough to make the rectangle visible
    • Parameters
      child View: The direct child making the request.
      rect Rect: The rectangle in the child's coordinates the child wishes to be on the screen.
      immediate boolean: True to forbid animated or delayed scrolling, false otherwise
      Returns
      boolean Whether the group scrolled to handle the operation

requestDisallowInterceptTouchEvent

void requestDisallowInterceptTouchEvent (boolean disallowIntercept)

Called when a child does not want this parent and its ancestors to intercept touch events with onInterceptTouchEvent(MotionEvent).

This parent should pass this call onto its parents. This parent must obey this request for the duration of the touch (that is, only clear the flag after this parent has received an up or a cancel.

Parameters
disallowIntercept boolean: True if the child does not want the parent to intercept touch events.

requestLayout

void requestLayout ()

Call this when something has changed which has invalidated the layout of this view. This will schedule a layout pass of the view tree. This should not be called while the view hierarchy is currently in a layout pass (isInLayout(). If layout is happening, the request may be honored at the end of the current layout pass (and then layout will run again) or after the current frame is drawn and the next layout occurs.

Subclasses which override this method should call the superclass method to handle possible request-during-layout errors correctly.

scrollBy

void scrollBy (int x, 
                int y)

Move the scrolled position of your view. This will cause a call to onScrollChanged(int, int, int, int) and the view will be invalidated.

Parameters
x int: the amount of pixels to scroll by horizontally
y int: the amount of pixels to scroll by vertically

scrollTo

void scrollTo (int x, 
                int y)

Set the scrolled position of your view. This will cause a call to onScrollChanged(int, int, int, int) and the view will be invalidated.

Parameters
x int: the x position to scroll to
y int: the y position to scroll to

scrollToPosition

void scrollToPosition (int position)

Convenience method to scroll to a certain position. RecyclerView does not implement scrolling logic, rather forwards the call to scrollToPosition(int)

Parameters
position int: Scroll to this adapter position

See also:

sendAccessibilityEventUnchecked

void sendAccessibilityEventUnchecked (AccessibilityEvent event)

This method behaves exactly as sendAccessibilityEvent(int) but takes as an argument an empty AccessibilityEvent and does not perform a check whether accessibility is enabled.

If an View.AccessibilityDelegate has been specified via calling setAccessibilityDelegate(AccessibilityDelegate) its sendAccessibilityEventUnchecked(View, AccessibilityEvent) is responsible for handling this call.

Parameters
event AccessibilityEvent: The event to send.

setAccessibilityDelegateCompat

void setAccessibilityDelegateCompat (RecyclerViewAccessibilityDelegate accessibilityDelegate)

Sets the accessibility delegate compatibility implementation used by RecyclerView.

Parameters
accessibilityDelegate RecyclerViewAccessibilityDelegate: The accessibility delegate to be used by RecyclerView.

setAdapter

void setAdapter (Adapter adapter)

Set a new adapter to provide child views on demand.

When adapter is changed, all existing views are recycled back to the pool. If the pool has only one adapter, it will be cleared.

Parameters
adapter Adapter: The new adapter to set, or null to set no adapter.

See also:

setChildDrawingOrderCallback

void setChildDrawingOrderCallback (RecyclerView.ChildDrawingOrderCallback childDrawingOrderCallback)

Sets the RecyclerView.ChildDrawingOrderCallback to be used for drawing children.

See getChildDrawingOrder(int, int) for details. Calling this method will always call setChildrenDrawingOrderEnabled(boolean). The parameter will be true if childDrawingOrderCallback is not null, false otherwise.

Note that child drawing order may be overridden by View's elevation.

Parameters
childDrawingOrderCallback RecyclerView.ChildDrawingOrderCallback: The ChildDrawingOrderCallback to be used by the drawing system.

setClipToPadding

void setClipToPadding (boolean clipToPadding)

Sets whether this ViewGroup will clip its children to its padding and resize (but not clip) any EdgeEffect to the padded region, if padding is present.

By default, children are clipped to the padding of their parent ViewGroup. This clipping behavior is only enabled if padding is non-zero.

Parameters
clipToPadding boolean: true to clip children to the padding of the group, and resize (but not clip) any EdgeEffect to the padded region. False otherwise.

setHasFixedSize

void setHasFixedSize (boolean hasFixedSize)

RecyclerView can perform several optimizations if it can know in advance that RecyclerView's size is not affected by the adapter contents. RecyclerView can still change its size based on other factors (e.g. its parent's size) but this size calculation cannot depend on the size of its children or contents of its adapter (except the number of items in the adapter).

If your use of RecyclerView falls into this category, set this to true. It will allow RecyclerView to avoid invalidating the whole layout when its adapter contents change.

Parameters
hasFixedSize boolean: true if adapter changes cannot affect the size of the RecyclerView.

setItemAnimator

void setItemAnimator (RecyclerView.ItemAnimator animator)

Sets the RecyclerView.ItemAnimator that will handle animations involving changes to the items in this RecyclerView. By default, RecyclerView instantiates and uses an instance of DefaultItemAnimator. Whether item animations are enabled for the RecyclerView depends on the ItemAnimator and whether the LayoutManager supports item animations.

Parameters
animator RecyclerView.ItemAnimator: The ItemAnimator being set. If null, no animations will occur when changes occur to the items in this RecyclerView.

setItemViewCacheSize

void setItemViewCacheSize (int size)

Set the number of offscreen views to retain before adding them to the potentially shared recycled view pool.

The offscreen view cache stays aware of changes in the attached adapter, allowing a LayoutManager to reuse those views unmodified without needing to return to the adapter to rebind them.

Parameters
size int: Number of views to cache offscreen before returning them to the general recycled view pool

setLayoutFrozen

void setLayoutFrozen (boolean frozen)

Enable or disable layout and scroll. After setLayoutFrozen(true) is called, Layout requests will be postponed until setLayoutFrozen(false) is called; child views are not updated when RecyclerView is frozen, smoothScrollBy(int, int), scrollBy(int, int), scrollToPosition(int) and smoothScrollToPosition(int) are dropped; TouchEvents and GenericMotionEvents are dropped; onFocusSearchFailed(View, int, Recycler, State) will not be called.

setLayoutFrozen(true) does not prevent app from directly calling scrollToPosition(int), smoothScrollToPosition(RecyclerView, State, int).

setAdapter(Adapter) and swapAdapter(Adapter, boolean) will automatically stop frozen.

Note: Running ItemAnimator is not stopped automatically, it's caller's responsibility to call ItemAnimator.end().

Parameters
frozen boolean: true to freeze layout and scroll, false to re-enable.

setLayoutManager

void setLayoutManager (RecyclerView.LayoutManager layout)

Set the RecyclerView.LayoutManager that this RecyclerView will use.

In contrast to other adapter-backed views such as ListView or GridView, RecyclerView allows client code to provide custom layout arrangements for child views. These arrangements are controlled by the RecyclerView.LayoutManager. A LayoutManager must be provided for RecyclerView to function.

Several default strategies are provided for common uses such as lists and grids.

Parameters
layout RecyclerView.LayoutManager: LayoutManager to use

setNestedScrollingEnabled

void setNestedScrollingEnabled (boolean enabled)

Enable or disable nested scrolling for this view.

If this property is set to true the view will be permitted to initiate nested scrolling operations with a compatible parent view in the current hierarchy. If this view does not implement nested scrolling this will have no effect. Disabling nested scrolling while a nested scroll is in progress has the effect of stopping the nested scroll.

Parameters
enabled boolean: true to enable nested scrolling, false to disable

setOnFlingListener

void setOnFlingListener (RecyclerView.OnFlingListener onFlingListener)

Set a RecyclerView.OnFlingListener for this RecyclerView.

If the RecyclerView.OnFlingListener is set then it will receive calls to fling(int, int) and will be able to intercept them.

Parameters
onFlingListener RecyclerView.OnFlingListener: The RecyclerView.OnFlingListener instance.

setOnScrollListener

void setOnScrollListener (RecyclerView.OnScrollListener listener)

This method is deprecated.
Use addOnScrollListener(OnScrollListener) and removeOnScrollListener(OnScrollListener)

Set a listener that will be notified of any changes in scroll state or position.

Parameters
listener RecyclerView.OnScrollListener: Listener to set or null to clear

setPreserveFocusAfterLayout

void setPreserveFocusAfterLayout (boolean preserveFocusAfterLayout)

Set whether the RecyclerView should try to keep the same Item focused after a layout calculation or not.

Usually, LayoutManagers keep focused views visible before and after layout but sometimes, views may lose focus during a layout calculation as their state changes or they are replaced with another view due to type change or animation. In these cases, RecyclerView can request focus on the new view automatically.

Parameters
preserveFocusAfterLayout boolean: Whether RecyclerView should preserve focused Item during a layout calculations. Defaults to true.

See also:

setRecycledViewPool

void setRecycledViewPool (RecyclerView.RecycledViewPool pool)

Recycled view pools allow multiple RecyclerViews to share a common pool of scrap views. This can be useful if you have multiple RecyclerViews with adapters that use the same view types, for example if you have several data sets with the same kinds of item views displayed by a ViewPager.

Parameters
pool RecyclerView.RecycledViewPool: Pool to set. If this parameter is null a new pool will be created and used.

setRecyclerListener

void setRecyclerListener (RecyclerView.RecyclerListener listener)

Register a listener that will be notified whenever a child view is recycled.

This listener will be called when a LayoutManager or the RecyclerView decides that a child view is no longer needed. If an application associates expensive or heavyweight data with item views, this may be a good place to release or free those resources.

Parameters
listener RecyclerView.RecyclerListener: Listener to register, or null to clear

setScrollingTouchSlop

void setScrollingTouchSlop (int slopConstant)

Configure the scrolling touch slop for a specific use case. Set up the RecyclerView's scrolling motion threshold based on common usages. Valid arguments are TOUCH_SLOP_DEFAULT and TOUCH_SLOP_PAGING.

Parameters
slopConstant int: One of the TOUCH_SLOP_ constants representing the intended usage of this RecyclerView

setViewCacheExtension

void setViewCacheExtension (RecyclerView.ViewCacheExtension extension)

Sets a new RecyclerView.ViewCacheExtension to be used by the Recycler.

Parameters
extension RecyclerView.ViewCacheExtension: ViewCacheExtension to be used or null if you want to clear the existing one.

See also:

smoothScrollBy

void smoothScrollBy (int dx, 
                int dy)

Animate a scroll by the given amount of pixels along either axis.

Parameters
dx int: Pixels to scroll horizontally
dy int: Pixels to scroll vertically

smoothScrollToPosition

void smoothScrollToPosition (int position)

Starts a smooth scroll to an adapter position.

To support smooth scrolling, you must override smoothScrollToPosition(RecyclerView, State, int) and create a RecyclerView.SmoothScroller.

RecyclerView.LayoutManager is responsible for creating the actual scroll action. If you want to provide a custom smooth scroll logic, override smoothScrollToPosition(RecyclerView, State, int) in your LayoutManager.

Parameters
position int: The adapter position to scroll to

See also:

startNestedScroll

boolean startNestedScroll (int axes)

Begin a nestable scroll operation along the given axes.

A view starting a nested scroll promises to abide by the following contract:

The view will call startNestedScroll upon initiating a scroll operation. In the case of a touch scroll this corresponds to the initial ACTION_DOWN. In the case of touch scrolling the nested scroll will be terminated automatically in the same manner as requestDisallowInterceptTouchEvent(boolean). In the event of programmatic scrolling the caller must explicitly call stopNestedScroll() to indicate the end of the nested scroll.

If startNestedScroll returns true, a cooperative parent was found. If it returns false the caller may ignore the rest of this contract until the next scroll. Calling startNestedScroll while a nested scroll is already in progress will return true.

At each incremental step of the scroll the caller should invoke dispatchNestedPreScroll once it has calculated the requested scrolling delta. If it returns true the nested scrolling parent at least partially consumed the scroll and the caller should adjust the amount it scrolls by.

After applying the remainder of the scroll delta the caller should invoke dispatchNestedScroll, passing both the delta consumed and the delta unconsumed. A nested scrolling parent may treat these values differently. See onNestedScroll(View, int, int, int, int).

Parameters
axes int: Flags consisting of a combination of SCROLL_AXIS_HORIZONTAL and/or SCROLL_AXIS_VERTICAL.
Returns
boolean true if a cooperative parent was found and nested scrolling has been enabled for the current gesture.

stopNestedScroll

void stopNestedScroll ()

Stop a nested scroll in progress.

Calling this method when a nested scroll is not currently in progress is harmless.

stopScroll

void stopScroll ()

Stop any current scroll in progress, such as one started by smoothScrollBy(int, int), fling(int, int) or a touch-initiated fling.

swapAdapter

void swapAdapter (Adapter adapter, 
                boolean removeAndRecycleExistingViews)

Swaps the current adapter with the provided one. It is similar to setAdapter(Adapter) but assumes existing adapter and the new adapter uses the same RecyclerView.ViewHolder and does not clear the RecycledViewPool.

Note that it still calls onAdapterChanged callbacks.

Parameters
adapter Adapter: The new adapter to set, or null to set no adapter.
removeAndRecycleExistingViews boolean: If set to true, RecyclerView will recycle all existing Views. If adapters have stable ids and/or you want to animate the disappearing views, you may prefer to set this to false.

See also:

Protected methods

checkLayoutParams

boolean checkLayoutParams (ViewGroup.LayoutParams p)

Parameters
p ViewGroup.LayoutParams
Returns
boolean

dispatchRestoreInstanceState

void dispatchRestoreInstanceState (SparseArray<Parcelable> container)

Override to prevent thawing of any views created by the adapter.

Parameters
container SparseArray: The SparseArray which holds previously saved state.

dispatchSaveInstanceState

void dispatchSaveInstanceState (SparseArray<Parcelable> container)

Override to prevent freezing of any views created by the adapter.

Parameters
container SparseArray: The SparseArray in which to save the view's state.

generateDefaultLayoutParams

ViewGroup.LayoutParams generateDefaultLayoutParams ()

Returns a set of default layout parameters. These parameters are requested when the View passed to addView(View) has no layout parameters already set. If null is returned, an exception is thrown from addView.

Returns
ViewGroup.LayoutParams a set of default layout parameters or null

generateLayoutParams

ViewGroup.LayoutParams generateLayoutParams (ViewGroup.LayoutParams p)

Returns a safe set of layout parameters based on the supplied layout params. When a ViewGroup is passed a View whose layout params do not pass the test of checkLayoutParams(android.view.ViewGroup.LayoutParams), this method is invoked. This method should return a new set of layout params suitable for this ViewGroup, possibly by copying the appropriate attributes from the specified set of layout params.

Parameters
p ViewGroup.LayoutParams: The layout parameters to convert into a suitable set of layout parameters for this ViewGroup.
Returns
ViewGroup.LayoutParams an instance of ViewGroup.LayoutParams or one of its descendants

getChildDrawingOrder

int getChildDrawingOrder (int childCount, 
                int i)

Returns the index of the child to draw for this iteration. Override this if you want to change the drawing order of children. By default, it returns i.

NOTE: In order for this method to be called, you must enable child ordering first by calling setChildrenDrawingOrderEnabled(boolean).

Parameters
childCount int
i int: The current iteration.
Returns
int The index of the child to draw this iteration.

onAttachedToWindow

void onAttachedToWindow ()

This is called when the view is attached to a window. At this point it has a Surface and will start drawing. Note that this function is guaranteed to be called before onDraw(android.graphics.Canvas), however it may be called any time before the first onDraw -- including before or after onMeasure(int, int).

onDetachedFromWindow

void onDetachedFromWindow ()

This is called when the view is detached from a window. At this point it no longer has a surface for drawing.

onLayout

void onLayout (boolean changed, 
                int l, 
                int t, 
                int r, 
                int b)

Called from layout when this view should assign a size and position to each of its children. Derived classes with children should override this method and call layout on each of their children.

Parameters
changed boolean: This is a new size or position for this view
l int: Left position, relative to parent
t int: Top position, relative to parent
r int: Right position, relative to parent
b int: Bottom position, relative to parent

onMeasure

void onMeasure (int widthSpec, 
                int heightSpec)

Measure the view and its content to determine the measured width and the measured height. This method is invoked by measure(int, int) and should be overridden by subclasses to provide accurate and efficient measurement of their contents.

CONTRACT: When overriding this method, you must call setMeasuredDimension(int, int) to store the measured width and height of this view. Failure to do so will trigger an IllegalStateException, thrown by measure(int, int). Calling the superclass' onMeasure(int, int) is a valid use.

The base class implementation of measure defaults to the background size, unless a larger size is allowed by the MeasureSpec. Subclasses should override onMeasure(int, int) to provide better measurements of their content.

If this method is overridden, it is the subclass's responsibility to make sure the measured height and width are at least the view's minimum height and width (getSuggestedMinimumHeight() and getSuggestedMinimumWidth()).

Parameters
widthSpec int: horizontal space requirements as imposed by the parent. The requirements are encoded with View.MeasureSpec.
heightSpec int: vertical space requirements as imposed by the parent. The requirements are encoded with View.MeasureSpec.

onRequestFocusInDescendants

boolean onRequestFocusInDescendants (int direction, 
                Rect previouslyFocusedRect)

Look for a descendant to call requestFocus() on. Called by requestFocus(int, android.graphics.Rect) when it wants to request focus within its children. Override this to customize how your ViewGroup requests focus within its children.

Parameters
direction int: One of FOCUS_UP, FOCUS_DOWN, FOCUS_LEFT, and FOCUS_RIGHT
previouslyFocusedRect Rect: The rectangle (in this View's coordinate system) to give a finer grained hint about where focus is coming from. May be null if there is no hint.
Returns
boolean Whether focus was taken.

onRestoreInstanceState

void onRestoreInstanceState (Parcelable state)

Hook allowing a view to re-apply a representation of its internal state that had previously been generated by onSaveInstanceState(). This function will never be called with a null state.

Parameters
state Parcelable: The frozen state that had previously been returned by onSaveInstanceState().

onSaveInstanceState

Parcelable onSaveInstanceState ()

Hook allowing a view to generate a representation of its internal state that can later be used to create a new instance with that same state. This state should only contain information that is not persistent or can not be reconstructed later. For example, you will never store your current position on screen because that will be computed again when a new instance of the view is placed in its view hierarchy.

Some examples of things you may store here: the current cursor position in a text view (but usually not the text itself since that is stored in a content provider or other persistent storage), the currently selected item in a list view.

Returns
Parcelable Returns a Parcelable object containing the view's current dynamic state, or null if there is nothing interesting to save. The default implementation returns null.

onSizeChanged

void onSizeChanged (int w, 
                int h, 
                int oldw, 
                int oldh)

This is called during layout when the size of this view has changed. If you were just added to the view hierarchy, you're called with the old values of 0.

Parameters
w int: Current width of this view.
h int: Current height of this view.
oldw int: Old width of this view.
oldh int: Old height of this view.

removeDetachedView

void removeDetachedView (View child, 
                boolean animate)

Finishes the removal of a detached view. This method will dispatch the detached from window event and notify the hierarchy change listener.

This method is intended to be lightweight and makes no assumptions about whether the parent or child should be redrawn. Proper use of this method will include also making any appropriate requestLayout() or invalidate() calls. For example, callers can post a Runnable which performs a requestLayout() on the next frame, after all detach/remove calls are finished, causing layout to be run prior to redrawing the view hierarchy.

Parameters
child View: the child to be definitely removed from the view hierarchy
animate boolean: if true and the view has an animation, the view is placed in the disappearing views list, otherwise, it is detached from the window
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