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.
RecyclerView.Adapter
responsible for providing views
that represent items in a data set.getChildAt(int)
. Contrast with Position.
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.
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 |
class |
RecyclerView.AdapterDataObserver
Observer base class for watching changes to an |
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 |
class |
RecyclerView.LayoutParams
|
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. |
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 |
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 ben 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 |
int |
TOUCH_SLOP_PAGING
Constant for use with |
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 |
void
|
addItemDecoration(RecyclerView.ItemDecoration decor, int index)
Add an |
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 |
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
|
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 |
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 |
RecyclerView.ViewHolder
|
getChildViewHolder(View child)
Retrieve the |
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 |
int
|
getMaxFlingVelocity()
Returns the maximum fling velocity used by this RecyclerView. |
int
|
getMinFlingVelocity()
Returns the minimum velocity to start a fling. |
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 |
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 |
void
|
offsetChildrenVertical(int dy)
Offset the bounds of all child views by |
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 |
void
|
removeOnChildAttachStateChangeListener(RecyclerView.OnChildAttachStateChangeListener listener)
Removes the provided listener from child attached state listeners list. |
void
|
removeOnItemTouchListener(RecyclerView.OnItemTouchListener listener)
Remove an |
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
|
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 |
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 |
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 |
void
|
setItemViewCacheSize(int size)
Set the number of offscreen views to retain before adding them to the potentially shared
|
void
|
setLayoutFrozen(boolean frozen)
Enable or disable layout and scroll. |
void
|
setLayoutManager(RecyclerView.LayoutManager layout)
Set the |
void
|
setNestedScrollingEnabled(boolean enabled)
Enable or disable nested scrolling for this view. |
void
|
setOnScrollListener(RecyclerView.OnScrollListener listener)
This method is deprecated.
Use |
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 |
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
|
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 |
void
|
onRestoreInstanceState(Parcelable state)
Hook allowing a view to re-apply a representation of its internal state that had previously
been generated by |
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
|
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;
int HORIZONTAL
Constant Value: 0 (0x00000000)
int INVALID_TYPE
Constant Value: -1 (0xffffffff)
long NO_ID
Constant Value: -1 (0xffffffffffffffff)
int NO_POSITION
Constant Value: -1 (0xffffffff)
int SCROLL_STATE_DRAGGING
The RecyclerView is currently being dragged by outside input such as user touch input.
See also:
Constant Value: 1 (0x00000001)
int SCROLL_STATE_IDLE
The RecyclerView is not currently scrolling.
See also:
Constant Value: 0 (0x00000000)
int SCROLL_STATE_SETTLING
The RecyclerView is currently animating to a final position while not under outside control.
See also:
Constant Value: 2 (0x00000002)
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)
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)
int VERTICAL
Constant Value: 1 (0x00000001)
RecyclerView (Context context, AttributeSet attrs)
Parameters | |
---|---|
context |
Context
|
attrs |
AttributeSet
|
RecyclerView (Context context, AttributeSet attrs, int defStyle)
Parameters | |
---|---|
context |
Context
|
attrs |
AttributeSet
|
defStyle |
int
|
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. |
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
|
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.
|
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
|
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:
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
|
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. 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 |
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:
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 |
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 |
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:
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 |
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 |
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:
dispatchNestedPreFling
; consume the fling and settle to a valid
position regardless.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 |
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 |
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. |
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.
|
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 |
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 |
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. |
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. |
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
|
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
|
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
|
RecyclerView.ViewHolder findViewHolderForPosition (int position)
This method is deprecated.
use findViewHolderForLayoutPosition(int)
or
findViewHolderForAdapterPosition(int)
Parameters | |
---|---|
position |
int
|
Returns | |
---|---|
RecyclerView.ViewHolder |
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. |
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 |
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
|
Adapter getAdapter ()
Retrieves the previously set adapter or null if no adapter is set.
Returns | |
---|---|
Adapter |
The previously set adapter |
See also:
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 |
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
|
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
|
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.
|
int getChildPosition (View child)
This method is deprecated.
use getChildAdapterPosition(View)
or
getChildLayoutPosition(View)
.
Parameters | |
---|---|
child |
View
|
Returns | |
---|---|
int |
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 |
RecyclerViewAccessibilityDelegate getCompatAccessibilityDelegate ()
Returns the accessibility delegate compatibility implementation used by the RecyclerView.
Returns | |
---|---|
RecyclerViewAccessibilityDelegate |
An instance of AccessibilityDelegateCompat used by RecyclerView |
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. |
RecyclerView.LayoutManager getLayoutManager ()
Return the RecyclerView.LayoutManager
currently responsible for
layout policy for this RecyclerView.
Returns | |
---|---|
RecyclerView.LayoutManager |
The currently bound LayoutManager |
int getMaxFlingVelocity ()
Returns the maximum fling velocity used by this RecyclerView.
Returns | |
---|---|
int |
The maximum fling velocity used by this RecyclerView. |
int getMinFlingVelocity ()
Returns the minimum velocity to start a fling.
Returns | |
---|---|
int |
The minimum velocity to start a fling |
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:
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:
int getScrollState ()
Return the current scrolling state of the RecyclerView.
Returns | |
---|---|
int |
SCROLL_STATE_IDLE , SCROLL_STATE_DRAGGING or
SCROLL_STATE_SETTLING
|
boolean hasFixedSize ()
Returns | |
---|---|
boolean |
true if the app has specified that changes in adapter content cannot change the size of the RecyclerView itself. |
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 |
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. |
void invalidateItemDecorations ()
Invalidates all ItemDecorations. If RecyclerView has item decorations, calling this method
will trigger a requestLayout()
call.
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. |
boolean isAttachedToWindow ()
Returns true if RecyclerView is attached to window.
Returns | |
---|---|
boolean |
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
|
boolean isLayoutFrozen ()
Returns true if layout and scroll are frozen.
Returns | |
---|---|
boolean |
true if layout and scroll are frozen |
See also:
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 |
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
|
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
|
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
|
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
|
void onDraw (Canvas c)
Implement this to do your drawing.
Parameters | |
---|---|
c |
Canvas :
the canvas on which the background will be drawn
|
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. |
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:
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. |
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
|
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
|
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:
ACTION_CLICK
when
accessibility features are enabled
Parameters | |
---|---|
e |
MotionEvent :
The motion event. |
Returns | |
---|---|
boolean |
True if the event was handled, false otherwise. |
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:
void removeOnChildAttachStateChangeListener (RecyclerView.OnChildAttachStateChangeListener listener)
Removes the provided listener from child attached state listeners list.
Parameters | |
---|---|
listener |
RecyclerView.OnChildAttachStateChangeListener :
Listener to unregister
|
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
|
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
|
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
|
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. ViewGroup
s overriding this can trust
that:
ViewGroup
s overriding this should uphold the contract:
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 |
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.
|
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.
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
|
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
|
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:
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. |
void setAccessibilityDelegateCompat (RecyclerViewAccessibilityDelegate accessibilityDelegate)
Sets the accessibility delegate compatibility implementation used by RecyclerView.
Parameters | |
---|---|
accessibilityDelegate |
RecyclerViewAccessibilityDelegate :
The accessibility delegate to be used by RecyclerView.
|
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:
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.
|
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. |
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.
|
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.
|
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
|
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.
|
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
|
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 |
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 |
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:
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.
|
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
|
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
|
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. |
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
|
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 |
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. |
void stopNestedScroll ()
Stop a nested scroll in progress.
Calling this method when a nested scroll is not currently in progress is harmless.
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. 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:
boolean checkLayoutParams (ViewGroup.LayoutParams p)
Parameters | |
---|---|
p |
ViewGroup.LayoutParams
|
Returns | |
---|---|
boolean |
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. |
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. |
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 |
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
|
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. |
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)
.
void onDetachedFromWindow ()
This is called when the view is detached from a window. At this point it no longer has a surface for drawing.
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
|
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 . |
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. |
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() . |
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. |
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.
|
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 |