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added in version 1.0.0
belongs to Maven artifact androidx.recyclerview:recyclerview:1.1.0-alpha01

LinearLayoutManager

public class LinearLayoutManager
extends RecyclerView.LayoutManager implements ItemTouchHelper.ViewDropHandler, RecyclerView.SmoothScroller.ScrollVectorProvider

java.lang.Object
   ↳ androidx.recyclerview.widget.RecyclerView.LayoutManager
     ↳ androidx.recyclerview.widget.LinearLayoutManager


A RecyclerView.LayoutManager implementation which provides similar functionality to ListView.

Summary

Nested classes

class LinearLayoutManager.LayoutChunkResult

 

XML attributes

RecyclerView_android_orientation  
RecyclerView_reverseLayout  
RecyclerView_stackFromEnd  

Inherited XML attributes

Constants

int HORIZONTAL

int INVALID_OFFSET

int VERTICAL

Public constructors

LinearLayoutManager(Context context)

Creates a vertical LinearLayoutManager

LinearLayoutManager(Context context, int orientation, boolean reverseLayout)
LinearLayoutManager(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes)

Constructor used when layout manager is set in XML by RecyclerView attribute "layoutManager".

Public methods

void assertNotInLayoutOrScroll(String message)

Checks if RecyclerView is in the middle of a layout or scroll and throws an IllegalStateException if it is.

boolean canScrollHorizontally()

Query if horizontal scrolling is currently supported.

boolean canScrollVertically()

Query if vertical scrolling is currently supported.

void collectAdjacentPrefetchPositions(int dx, int dy, RecyclerView.State state, RecyclerView.LayoutManager.LayoutPrefetchRegistry layoutPrefetchRegistry)

Gather all positions from the LayoutManager to be prefetched, given specified momentum.

void collectInitialPrefetchPositions(int adapterItemCount, RecyclerView.LayoutManager.LayoutPrefetchRegistry layoutPrefetchRegistry)

Gather all positions from the LayoutManager to be prefetched in preperation for its RecyclerView to come on screen, due to the movement of another, containing RecyclerView.

int computeHorizontalScrollExtent(RecyclerView.State state)

Override this method if you want to support scroll bars.

int computeHorizontalScrollOffset(RecyclerView.State state)

Override this method if you want to support scroll bars.

int computeHorizontalScrollRange(RecyclerView.State state)

Override this method if you want to support scroll bars.

PointF computeScrollVectorForPosition(int targetPosition)

Should calculate the vector that points to the direction where the target position can be found.

int computeVerticalScrollExtent(RecyclerView.State state)

Override this method if you want to support scroll bars.

int computeVerticalScrollOffset(RecyclerView.State state)

Override this method if you want to support scroll bars.

int computeVerticalScrollRange(RecyclerView.State state)

Override this method if you want to support scroll bars.

int findFirstCompletelyVisibleItemPosition()

Returns the adapter position of the first fully visible view.

int findFirstVisibleItemPosition()

Returns the adapter position of the first visible view.

int findLastCompletelyVisibleItemPosition()

Returns the adapter position of the last fully visible view.

int findLastVisibleItemPosition()

Returns the adapter position of the last visible view.

View findViewByPosition(int position)

Finds the view which represents the given adapter position.

RecyclerView.LayoutParams generateDefaultLayoutParams()

Create a default LayoutParams object for a child of the RecyclerView.

int getInitialPrefetchItemCount()

Gets the number of items to prefetch in collectInitialPrefetchPositions(int, LayoutPrefetchRegistry), which defines how many inner items should be prefetched when this LayoutManager's RecyclerView is nested inside another RecyclerView.

int getOrientation()

Returns the current orientation of the layout.

boolean getRecycleChildrenOnDetach()

Returns whether LayoutManager will recycle its children when it is detached from RecyclerView.

boolean getReverseLayout()

Returns if views are laid out from the opposite direction of the layout.

boolean getStackFromEnd()
boolean isAutoMeasureEnabled()

Returns whether the measuring pass of layout should use the AutoMeasure mechanism of RecyclerView or if it should be done by the LayoutManager's implementation of onMeasure(Recycler, State, int, int).

boolean isSmoothScrollbarEnabled()

Returns the current state of the smooth scrollbar feature.

void onDetachedFromWindow(RecyclerView view, RecyclerView.Recycler recycler)

Called when this LayoutManager is detached from its parent RecyclerView or when its parent RecyclerView is detached from its window.

View onFocusSearchFailed(View focused, int focusDirection, RecyclerView.Recycler recycler, RecyclerView.State state)

Called when searching for a focusable view in the given direction has failed for the current content of the RecyclerView.

void onInitializeAccessibilityEvent(AccessibilityEvent event)
void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state)

Lay out all relevant child views from the given adapter.

void onLayoutCompleted(RecyclerView.State state)

Called after a full layout calculation is finished.

void onRestoreInstanceState(Parcelable state)
Parcelable onSaveInstanceState()

Called when the LayoutManager should save its state.

int scrollHorizontallyBy(int dx, RecyclerView.Recycler recycler, RecyclerView.State state)

Scroll horizontally by dx pixels in screen coordinates and return the distance traveled.

void scrollToPosition(int position)

Scroll the RecyclerView to make the position visible.

void scrollToPositionWithOffset(int position, int offset)

Scroll to the specified adapter position with the given offset from resolved layout start.

int scrollVerticallyBy(int dy, RecyclerView.Recycler recycler, RecyclerView.State state)

Scroll vertically by dy pixels in screen coordinates and return the distance traveled.

void setInitialPrefetchItemCount(int itemCount)

Sets the number of items to prefetch in collectInitialPrefetchPositions(int, LayoutPrefetchRegistry), which defines how many inner items should be prefetched when this LayoutManager's RecyclerView is nested inside another RecyclerView.

void setOrientation(int orientation)

Sets the orientation of the layout.

void setRecycleChildrenOnDetach(boolean recycleChildrenOnDetach)

Set whether LayoutManager will recycle its children when it is detached from RecyclerView.

void setReverseLayout(boolean reverseLayout)

Used to reverse item traversal and layout order.

void setSmoothScrollbarEnabled(boolean enabled)

When smooth scrollbar is enabled, the position and size of the scrollbar thumb is computed based on the number of visible pixels in the visible items.

void setStackFromEnd(boolean stackFromEnd)

Compatibility support for AbsListView.setStackFromBottom(boolean)

void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state, int position)

Smooth scroll to the specified adapter position.

boolean supportsPredictiveItemAnimations()

Returns whether this LayoutManager supports "predictive item animations".

Protected methods

int getExtraLayoutSpace(RecyclerView.State state)

Returns the amount of extra space that should be laid out by LayoutManager.

boolean isLayoutRTL()

Inherited methods

XML attributes

RecyclerView_android_orientation

Related methods:

RecyclerView_reverseLayout

Related methods:

RecyclerView_stackFromEnd

Related methods:

Constants

HORIZONTAL

added in version 1.0.0
public static final int HORIZONTAL

Constant Value: 0 (0x00000000)

INVALID_OFFSET

added in version 1.0.0
public static final int INVALID_OFFSET

Constant Value: -2147483648 (0x80000000)

VERTICAL

added in version 1.0.0
public static final int VERTICAL

Constant Value: 1 (0x00000001)

Public constructors

LinearLayoutManager

added in version 1.0.0
public LinearLayoutManager (Context context)

Creates a vertical LinearLayoutManager

Parameters
context Context: Current context, will be used to access resources.

LinearLayoutManager

added in version 1.0.0
public LinearLayoutManager (Context context, 
                int orientation, 
                boolean reverseLayout)

Parameters
context Context: Current context, will be used to access resources.

orientation int: Layout orientation. Should be HORIZONTAL or VERTICAL.

reverseLayout boolean: When set to true, layouts from end to start.

LinearLayoutManager

added in version 1.0.0
public LinearLayoutManager (Context context, 
                AttributeSet attrs, 
                int defStyleAttr, 
                int defStyleRes)

Constructor used when layout manager is set in XML by RecyclerView attribute "layoutManager". Defaults to vertical orientation.

Related XML Attributes:

Parameters
context Context

attrs AttributeSet

defStyleAttr int

defStyleRes int

Public methods

assertNotInLayoutOrScroll

added in version 1.0.0
public void assertNotInLayoutOrScroll (String message)

Checks if RecyclerView is in the middle of a layout or scroll and throws an IllegalStateException if it is.

Parameters
message String: The message for the exception. Can be null.

canScrollHorizontally

added in version 1.0.0
public boolean canScrollHorizontally ()

Query if horizontal scrolling is currently supported. The default implementation returns false.

Returns
boolean true if getOrientation() is HORIZONTAL

canScrollVertically

added in version 1.0.0
public boolean canScrollVertically ()

Query if vertical scrolling is currently supported. The default implementation returns false.

Returns
boolean true if getOrientation() is VERTICAL

collectAdjacentPrefetchPositions

added in version 1.0.0
public void collectAdjacentPrefetchPositions (int dx, 
                int dy, 
                RecyclerView.State state, 
                RecyclerView.LayoutManager.LayoutPrefetchRegistry layoutPrefetchRegistry)

Gather all positions from the LayoutManager to be prefetched, given specified momentum.

If item prefetch is enabled, this method is called in between traversals to gather which positions the LayoutManager will soon need, given upcoming movement in subsequent traversals.

The LayoutManager should call RecyclerView.LayoutManager.LayoutPrefetchRegistry.addPosition(int, int) for each item to be prepared, and these positions will have their ViewHolders created and bound, if there is sufficient time available, in advance of being needed by a scroll or layout.

Parameters
dx int: X movement component.

dy int: Y movement component.

state RecyclerView.State: State of RecyclerView

layoutPrefetchRegistry RecyclerView.LayoutManager.LayoutPrefetchRegistry: PrefetchRegistry to add prefetch entries into.

collectInitialPrefetchPositions

added in version 1.0.0
public void collectInitialPrefetchPositions (int adapterItemCount, 
                RecyclerView.LayoutManager.LayoutPrefetchRegistry layoutPrefetchRegistry)

Gather all positions from the LayoutManager to be prefetched in preperation for its RecyclerView to come on screen, due to the movement of another, containing RecyclerView.

This method is only called when a RecyclerView is nested in another RecyclerView.

If item prefetch is enabled for this LayoutManager, as well in another containing LayoutManager, this method is called in between draw traversals to gather which positions this LayoutManager will first need, once it appears on the screen.

For example, if this LayoutManager represents a horizontally scrolling list within a vertically scrolling LayoutManager, this method would be called when the horizontal list is about to come onscreen.

The LayoutManager should call RecyclerView.LayoutManager.LayoutPrefetchRegistry.addPosition(int, int) for each item to be prepared, and these positions will have their ViewHolders created and bound, if there is sufficient time available, in advance of being needed by a scroll or layout.

Parameters
adapterItemCount int: number of items in the associated adapter.

layoutPrefetchRegistry RecyclerView.LayoutManager.LayoutPrefetchRegistry: PrefetchRegistry to add prefetch entries into.

computeHorizontalScrollExtent

added in version 1.0.0
public int computeHorizontalScrollExtent (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read RecyclerView.computeHorizontalScrollExtent() for details.

Default implementation returns 0.

Parameters
state RecyclerView.State: Current state of RecyclerView

Returns
int The horizontal extent of the scrollbar's thumb

computeHorizontalScrollOffset

added in version 1.0.0
public int computeHorizontalScrollOffset (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read RecyclerView.computeHorizontalScrollOffset() for details.

Default implementation returns 0.

Parameters
state RecyclerView.State: Current State of RecyclerView where you can find total item count

Returns
int The horizontal offset of the scrollbar's thumb

computeHorizontalScrollRange

added in version 1.0.0
public int computeHorizontalScrollRange (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read RecyclerView.computeHorizontalScrollRange() for details.

Default implementation returns 0.

Parameters
state RecyclerView.State: Current State of RecyclerView where you can find total item count

Returns
int The total horizontal range represented by the vertical scrollbar

computeScrollVectorForPosition

added in version 1.0.0
public PointF computeScrollVectorForPosition (int targetPosition)

Should calculate the vector that points to the direction where the target position can be found.

This method is used by the LinearSmoothScroller to initiate a scroll towards the target position.

The magnitude of the vector is not important. It is always normalized before being used by the LinearSmoothScroller.

LayoutManager should not check whether the position exists in the adapter or not.

Parameters
targetPosition int: the target position to which the returned vector should point

Returns
PointF the scroll vector for a given position.

computeVerticalScrollExtent

added in version 1.0.0
public int computeVerticalScrollExtent (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read RecyclerView.computeVerticalScrollExtent() for details.

Default implementation returns 0.

Parameters
state RecyclerView.State: Current state of RecyclerView

Returns
int The vertical extent of the scrollbar's thumb

computeVerticalScrollOffset

added in version 1.0.0
public int computeVerticalScrollOffset (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read RecyclerView.computeVerticalScrollOffset() for details.

Default implementation returns 0.

Parameters
state RecyclerView.State: Current State of RecyclerView where you can find total item count

Returns
int The vertical offset of the scrollbar's thumb

computeVerticalScrollRange

added in version 1.0.0
public int computeVerticalScrollRange (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read RecyclerView.computeVerticalScrollRange() for details.

Default implementation returns 0.

Parameters
state RecyclerView.State: Current State of RecyclerView where you can find total item count

Returns
int The total vertical range represented by the vertical scrollbar

findFirstCompletelyVisibleItemPosition

added in version 1.0.0
public int findFirstCompletelyVisibleItemPosition ()

Returns the adapter position of the first fully visible view. This position does not include adapter changes that were dispatched after the last layout pass.

Note that bounds check is only performed in the current orientation. That means, if LayoutManager is horizontal, it will only check the view's left and right edges.

Returns
int The adapter position of the first fully visible item or RecyclerView.NO_POSITION if there aren't any visible items.

findFirstVisibleItemPosition

added in version 1.0.0
public int findFirstVisibleItemPosition ()

Returns the adapter position of the first visible view. This position does not include adapter changes that were dispatched after the last layout pass.

Note that, this value is not affected by layout orientation or item order traversal. (setReverseLayout(boolean)). Views are sorted by their positions in the adapter, not in the layout.

If RecyclerView has item decorators, they will be considered in calculations as well.

LayoutManager may pre-cache some views that are not necessarily visible. Those views are ignored in this method.

Returns
int The adapter position of the first visible item or RecyclerView.NO_POSITION if there aren't any visible items.

findLastCompletelyVisibleItemPosition

added in version 1.0.0
public int findLastCompletelyVisibleItemPosition ()

Returns the adapter position of the last fully visible view. This position does not include adapter changes that were dispatched after the last layout pass.

Note that bounds check is only performed in the current orientation. That means, if LayoutManager is horizontal, it will only check the view's left and right edges.

Returns
int The adapter position of the last fully visible view or RecyclerView.NO_POSITION if there aren't any visible items.

findLastVisibleItemPosition

added in version 1.0.0
public int findLastVisibleItemPosition ()

Returns the adapter position of the last visible view. This position does not include adapter changes that were dispatched after the last layout pass.

Note that, this value is not affected by layout orientation or item order traversal. (setReverseLayout(boolean)). Views are sorted by their positions in the adapter, not in the layout.

If RecyclerView has item decorators, they will be considered in calculations as well.

LayoutManager may pre-cache some views that are not necessarily visible. Those views are ignored in this method.

Returns
int The adapter position of the last visible view or RecyclerView.NO_POSITION if there aren't any visible items.

findViewByPosition

added in version 1.0.0
public View findViewByPosition (int position)

Finds the view which represents the given adapter position.

This method traverses each child since it has no information about child order. Override this method to improve performance if your LayoutManager keeps data about child views.

If a view is ignored via ignoreView(View), it is also ignored by this method.

Parameters
position int: Position of the item in adapter

Returns
View The child view that represents the given position or null if the position is not laid out

generateDefaultLayoutParams

added in version 1.0.0
public RecyclerView.LayoutParams generateDefaultLayoutParams ()

Create a default LayoutParams object for a child of the RecyclerView.

LayoutManagers will often want to use a custom LayoutParams type to store extra information specific to the layout. Client code should subclass RecyclerView.LayoutParams for this purpose.

Important: if you use your own custom LayoutParams type you must also override checkLayoutParams(LayoutParams), generateLayoutParams(android.view.ViewGroup.LayoutParams) and generateLayoutParams(android.content.Context, android.util.AttributeSet).

Returns
RecyclerView.LayoutParams A new LayoutParams for a child view

getInitialPrefetchItemCount

added in version 1.0.0
public int getInitialPrefetchItemCount ()

Gets the number of items to prefetch in collectInitialPrefetchPositions(int, LayoutPrefetchRegistry), which defines how many inner items should be prefetched when this LayoutManager's RecyclerView is nested inside another RecyclerView.

Returns
int number of items to prefetch.

getOrientation

added in version 1.0.0
public int getOrientation ()

Returns the current orientation of the layout.

Returns
int Current orientation, either HORIZONTAL or VERTICAL

getRecycleChildrenOnDetach

added in version 1.0.0
public boolean getRecycleChildrenOnDetach ()

Returns whether LayoutManager will recycle its children when it is detached from RecyclerView.

Returns
boolean true if LayoutManager will recycle its children when it is detached from RecyclerView.

getReverseLayout

added in version 1.0.0
public boolean getReverseLayout ()

Returns if views are laid out from the opposite direction of the layout.

Returns
boolean If layout is reversed or not.

getStackFromEnd

added in version 1.0.0
public boolean getStackFromEnd ()

Returns
boolean

isAutoMeasureEnabled

added in version 1.0.0
public boolean isAutoMeasureEnabled ()

Returns whether the measuring pass of layout should use the AutoMeasure mechanism of RecyclerView or if it should be done by the LayoutManager's implementation of onMeasure(Recycler, State, int, int).

This method returns false by default (it actually returns the value passed to the deprecated setAutoMeasureEnabled(boolean)) and should be overridden to return true if a LayoutManager wants to be auto measured by the RecyclerView.

If this method is overridden to return true, onMeasure(Recycler, State, int, int) should not be overridden.

AutoMeasure is a RecyclerView mechanism that handles the measuring pass of layout in a simple and contract satisfying way, including the wrapping of children laid out by LayoutManager. Simply put, it handles wrapping children by calling onLayoutChildren(Recycler, State) during a call to RecyclerView.onMeasure(int, int), and then calculating desired dimensions based on children's dimensions and positions. It does this while supporting all existing animation capabilities of the RecyclerView.

More specifically:

  1. When RecyclerView.onMeasure(int, int) is called, if the provided measure specs both have a mode of View.MeasureSpec.EXACTLY, RecyclerView will set its measured dimensions accordingly and return, allowing layout to continue as normal (Actually, RecyclerView will call onMeasure(Recycler, State, int, int) for backwards compatibility reasons but it should not be overridden if AutoMeasure is being used).
  2. If one of the layout specs is not EXACT, the RecyclerView will start the layout process. It will first process all pending Adapter updates and then decide whether to run a predictive layout. If it decides to do so, it will first call onLayoutChildren(Recycler, State) with RecyclerView.State.isPreLayout() set to true. At this stage, getWidth() and getHeight() will still return the width and height of the RecyclerView as of the last layout calculation.

    After handling the predictive case, RecyclerView will call onLayoutChildren(Recycler, State) with RecyclerView.State.isMeasuring() set to true and RecyclerView.State.isPreLayout() set to false. The LayoutManager can access the measurement specs via getHeight(), getHeightMode(), getWidth() and getWidthMode().

  3. After the layout calculation, RecyclerView sets the measured width & height by calculating the bounding box for the children (+ RecyclerView's padding). The LayoutManagers can override setMeasuredDimension(Rect, int, int) to choose different values. For instance, GridLayoutManager overrides this value to handle the case where if it is vertical and has 3 columns but only 2 items, it should still measure its width to fit 3 items, not 2.
  4. Any following calls to RecyclerView.onMeasure(int, int) will run onLayoutChildren(Recycler, State) with RecyclerView.State.isMeasuring() set to true and RecyclerView.State.isPreLayout() set to false. RecyclerView will take care of which views are actually added / removed / moved / changed for animations so that the LayoutManager should not worry about them and handle each onLayoutChildren(Recycler, State) call as if it is the last one.
  5. When measure is complete and RecyclerView's RecyclerView.onLayout(boolean, int, int, int, int) method is called, RecyclerView checks whether it already did layout calculations during the measure pass and if so, it re-uses that information. It may still decide to call onLayoutChildren(Recycler, State) if the last measure spec was different from the final dimensions or adapter contents have changed between the measure call and the layout call.
  6. Finally, animations are calculated and run as usual.

Returns
boolean True if the measuring pass of layout should use the AutoMeasure mechanism of RecyclerView or False if it should be done by the LayoutManager's implementation of onMeasure(Recycler, State, int, int).

isSmoothScrollbarEnabled

added in version 1.0.0
public boolean isSmoothScrollbarEnabled ()

Returns the current state of the smooth scrollbar feature. It is enabled by default.

Returns
boolean True if smooth scrollbar is enabled, false otherwise.

onDetachedFromWindow

added in version 1.0.0
public void onDetachedFromWindow (RecyclerView view, 
                RecyclerView.Recycler recycler)

Called when this LayoutManager is detached from its parent RecyclerView or when its parent RecyclerView is detached from its window.

LayoutManager should clear all of its View references as another LayoutManager might be assigned to the RecyclerView.

If the RecyclerView is re-attached with the same LayoutManager and Adapter, it may not call onLayoutChildren(Recycler, State) if nothing has changed and a layout was not requested on the RecyclerView while it was detached.

If your LayoutManager has View references that it cleans in on-detach, it should also call RecyclerView.requestLayout() to ensure that it is re-laid out when RecyclerView is re-attached.

Subclass implementations should always call through to the superclass implementation.

Parameters
view RecyclerView: The RecyclerView this LayoutManager is bound to

recycler RecyclerView.Recycler: The recycler to use if you prefer to recycle your children instead of keeping them around.

onFocusSearchFailed

added in version 1.0.0
public View onFocusSearchFailed (View focused, 
                int focusDirection, 
                RecyclerView.Recycler recycler, 
                RecyclerView.State state)

Called when searching for a focusable view in the given direction has failed for the current content of the RecyclerView.

This is the LayoutManager's opportunity to populate views in the given direction to fulfill the request if it can. The LayoutManager should attach and return the view to be focused, if a focusable view in the given direction is found. Otherwise, if all the existing (or the newly populated views) are unfocusable, it returns the next unfocusable view to become visible on the screen. This unfocusable view is typically the first view that's either partially or fully out of RV's padded bounded area in the given direction. The default implementation returns null.

Parameters
focused View: The currently focused view

focusDirection int: One of View.FOCUS_UP, View.FOCUS_DOWN, View.FOCUS_LEFT, View.FOCUS_RIGHT, View.FOCUS_BACKWARD, View.FOCUS_FORWARD or 0 for not applicable

recycler RecyclerView.Recycler: The recycler to use for obtaining views for currently offscreen items

state RecyclerView.State: Transient state of RecyclerView

Returns
View The chosen view to be focused if a focusable view is found, otherwise an unfocusable view to become visible onto the screen, else null.

onInitializeAccessibilityEvent

added in version 1.0.0
public void onInitializeAccessibilityEvent (AccessibilityEvent event)

Parameters
event AccessibilityEvent

onLayoutChildren

added in version 1.0.0
public void onLayoutChildren (RecyclerView.Recycler recycler, 
                RecyclerView.State state)

Lay out all relevant child views from the given adapter. The LayoutManager is in charge of the behavior of item animations. By default, RecyclerView has a non-null ItemAnimator, and simple item animations are enabled. This means that add/remove operations on the adapter will result in animations to add new or appearing items, removed or disappearing items, and moved items. If a LayoutManager returns false from supportsPredictiveItemAnimations(), which is the default, and runs a normal layout operation during onLayoutChildren(Recycler, State), the RecyclerView will have enough information to run those animations in a simple way. For example, the default ItemAnimator, DefaultItemAnimator, will simply fade views in and out, whether they are actually added/removed or whether they are moved on or off the screen due to other add/remove operations.

A LayoutManager wanting a better item animation experience, where items can be animated onto and off of the screen according to where the items exist when they are not on screen, then the LayoutManager should return true from supportsPredictiveItemAnimations() and add additional logic to onLayoutChildren(Recycler, State). Supporting predictive animations means that onLayoutChildren(Recycler, State) will be called twice; once as a "pre" layout step to determine where items would have been prior to a real layout, and again to do the "real" layout. In the pre-layout phase, items will remember their pre-layout positions to allow them to be laid out appropriately. Also, removed items will be returned from the scrap to help determine correct placement of other items. These removed items should not be added to the child list, but should be used to help calculate correct positioning of other views, including views that were not previously onscreen (referred to as APPEARING views), but whose pre-layout offscreen position can be determined given the extra information about the pre-layout removed views.

The second layout pass is the real layout in which only non-removed views will be used. The only additional requirement during this pass is, if supportsPredictiveItemAnimations() returns true, to note which views exist in the child list prior to layout and which are not there after layout (referred to as DISAPPEARING views), and to position/layout those views appropriately, without regard to the actual bounds of the RecyclerView. This allows the animation system to know the location to which to animate these disappearing views.

The default LayoutManager implementations for RecyclerView handle all of these requirements for animations already. Clients of RecyclerView can either use one of these layout managers directly or look at their implementations of onLayoutChildren() to see how they account for the APPEARING and DISAPPEARING views.

Parameters
recycler RecyclerView.Recycler: Recycler to use for fetching potentially cached views for a position

state RecyclerView.State: Transient state of RecyclerView

onLayoutCompleted

added in version 1.0.0
public void onLayoutCompleted (RecyclerView.State state)

Called after a full layout calculation is finished. The layout calculation may include multiple onLayoutChildren(Recycler, State) calls due to animations or layout measurement but it will include only one onLayoutCompleted(State) call. This method will be called at the end of View.layout(int, int, int, int) call.

This is a good place for the LayoutManager to do some cleanup like pending scroll position, saved state etc.

Parameters
state RecyclerView.State: Transient state of RecyclerView

onRestoreInstanceState

added in version 1.0.0
public void onRestoreInstanceState (Parcelable state)

Parameters
state Parcelable

onSaveInstanceState

added in version 1.0.0
public Parcelable onSaveInstanceState ()

Called when the LayoutManager should save its state. This is a good time to save your scroll position, configuration and anything else that may be required to restore the same layout state if the LayoutManager is recreated.

RecyclerView does NOT verify if the LayoutManager has changed between state save and restore. This will let you share information between your LayoutManagers but it is also your responsibility to make sure they use the same parcelable class.

Returns
Parcelable Necessary information for LayoutManager to be able to restore its state

scrollHorizontallyBy

added in version 1.0.0
public int scrollHorizontallyBy (int dx, 
                RecyclerView.Recycler recycler, 
                RecyclerView.State state)

Scroll horizontally by dx pixels in screen coordinates and return the distance traveled. The default implementation does nothing and returns 0.

Parameters
dx int: distance to scroll by in pixels. X increases as scroll position approaches the right.

recycler RecyclerView.Recycler: Recycler to use for fetching potentially cached views for a position

state RecyclerView.State: Transient state of RecyclerView

Returns
int The actual distance scrolled. The return value will be negative if dx was negative and scrolling proceeeded in that direction. Math.abs(result) may be less than dx if a boundary was reached.

scrollToPosition

added in version 1.0.0
public void scrollToPosition (int position)

Scroll the RecyclerView to make the position visible.

RecyclerView will scroll the minimum amount that is necessary to make the target position visible. If you are looking for a similar behavior to ListView.setSelection(int) or AbsListView.setSelectionFromTop(int, int), use scrollToPositionWithOffset(int, int).

Note that scroll position change will not be reflected until the next layout call.

Parameters
position int: Scroll to this adapter position

scrollToPositionWithOffset

added in version 1.0.0
public void scrollToPositionWithOffset (int position, 
                int offset)

Scroll to the specified adapter position with the given offset from resolved layout start. Resolved layout start depends on getReverseLayout(), ViewCompat.getLayoutDirection(android.view.View) and getStackFromEnd().

For example, if layout is VERTICAL and getStackFromEnd() is true, calling scrollToPositionWithOffset(10, 20) will layout such that item[10]'s bottom is 20 pixels above the RecyclerView's bottom.

Note that scroll position change will not be reflected until the next layout call.

If you are just trying to make a position visible, use scrollToPosition(int).

Parameters
position int: Index (starting at 0) of the reference item.

offset int: The distance (in pixels) between the start edge of the item view and start edge of the RecyclerView.

scrollVerticallyBy

added in version 1.0.0
public int scrollVerticallyBy (int dy, 
                RecyclerView.Recycler recycler, 
                RecyclerView.State state)

Scroll vertically by dy pixels in screen coordinates and return the distance traveled. The default implementation does nothing and returns 0.

Parameters
dy int: distance to scroll in pixels. Y increases as scroll position approaches the bottom.

recycler RecyclerView.Recycler: Recycler to use for fetching potentially cached views for a position

state RecyclerView.State: Transient state of RecyclerView

Returns
int The actual distance scrolled. The return value will be negative if dy was negative and scrolling proceeeded in that direction. Math.abs(result) may be less than dy if a boundary was reached.

setInitialPrefetchItemCount

added in version 1.0.0
public void setInitialPrefetchItemCount (int itemCount)

Sets the number of items to prefetch in collectInitialPrefetchPositions(int, LayoutPrefetchRegistry), which defines how many inner items should be prefetched when this LayoutManager's RecyclerView is nested inside another RecyclerView.

Set this value to the number of items this inner LayoutManager will display when it is first scrolled into the viewport. RecyclerView will attempt to prefetch that number of items so they are ready, avoiding jank as the inner RecyclerView is scrolled into the viewport.

For example, take a vertically scrolling RecyclerView with horizontally scrolling inner RecyclerViews. The rows always have 4 items visible in them (or 5 if not aligned). Passing 4 to this method for each inner RecyclerView's LinearLayoutManager will enable RecyclerView's prefetching feature to do create/bind work for 4 views within a row early, before it is scrolled on screen, instead of just the default 2.

Calling this method does nothing unless the LayoutManager is in a RecyclerView nested in another RecyclerView.

Note: Setting this value to be larger than the number of views that will be visible in this view can incur unnecessary bind work, and an increase to the number of Views created and in active use.

Parameters
itemCount int: Number of items to prefetch

setOrientation

added in version 1.0.0
public void setOrientation (int orientation)

Sets the orientation of the layout. LinearLayoutManager will do its best to keep scroll position.

Parameters
orientation int: HORIZONTAL or VERTICAL

setRecycleChildrenOnDetach

added in version 1.0.0
public void setRecycleChildrenOnDetach (boolean recycleChildrenOnDetach)

Set whether LayoutManager will recycle its children when it is detached from RecyclerView.

If you are using a RecyclerView.RecycledViewPool, it might be a good idea to set this flag to true so that views will be available to other RecyclerViews immediately.

Note that, setting this flag will result in a performance drop if RecyclerView is restored.

Parameters
recycleChildrenOnDetach boolean: Whether children should be recycled in detach or not.

setReverseLayout

added in version 1.0.0
public void setReverseLayout (boolean reverseLayout)

Used to reverse item traversal and layout order. This behaves similar to the layout change for RTL views. When set to true, first item is laid out at the end of the UI, second item is laid out before it etc. For horizontal layouts, it depends on the layout direction. When set to true, If RecyclerView is LTR, than it will layout from RTL, if RecyclerView} is RTL, it will layout from LTR. If you are looking for the exact same behavior of AbsListView.setStackFromBottom(boolean), use setStackFromEnd(boolean)

Parameters
reverseLayout boolean

setSmoothScrollbarEnabled

added in version 1.0.0
public void setSmoothScrollbarEnabled (boolean enabled)

When smooth scrollbar is enabled, the position and size of the scrollbar thumb is computed based on the number of visible pixels in the visible items. This however assumes that all list items have similar or equal widths or heights (depending on list orientation). If you use a list in which items have different dimensions, the scrollbar will change appearance as the user scrolls through the list. To avoid this issue, you need to disable this property. When smooth scrollbar is disabled, the position and size of the scrollbar thumb is based solely on the number of items in the adapter and the position of the visible items inside the adapter. This provides a stable scrollbar as the user navigates through a list of items with varying widths / heights.

Parameters
enabled boolean: Whether or not to enable smooth scrollbar.

setStackFromEnd

added in version 1.0.0
public void setStackFromEnd (boolean stackFromEnd)

Compatibility support for AbsListView.setStackFromBottom(boolean)

Parameters
stackFromEnd boolean

smoothScrollToPosition

added in version 1.0.0
public void smoothScrollToPosition (RecyclerView recyclerView, 
                RecyclerView.State state, 
                int position)

Smooth scroll to the specified adapter position.

To support smooth scrolling, override this method, create your RecyclerView.SmoothScroller instance and call startSmoothScroll(SmoothScroller).

Parameters
recyclerView RecyclerView: The RecyclerView to which this layout manager is attached

state RecyclerView.State: Current State of RecyclerView

position int: Scroll to this adapter position.

supportsPredictiveItemAnimations

added in version 1.0.0
public boolean supportsPredictiveItemAnimations ()

Returns whether this LayoutManager supports "predictive item animations".

"Predictive item animations" are automatically created animations that show where items came from, and where they are going to, as items are added, removed, or moved within a layout.

A LayoutManager wishing to support predictive item animations must override this method to return true (the default implementation returns false) and must obey certain behavioral contracts outlined in onLayoutChildren(Recycler, State).

Whether item animations actually occur in a RecyclerView is actually determined by both the return value from this method and the ItemAnimator set on the RecyclerView itself. If the RecyclerView has a non-null ItemAnimator but this method returns false, then only "simple item animations" will be enabled in the RecyclerView, in which views whose position are changing are simply faded in/out. If the RecyclerView has a non-null ItemAnimator and this method returns true, then predictive item animations will be enabled in the RecyclerView.

Returns
boolean true if this LayoutManager supports predictive item animations, false otherwise.

Protected methods

getExtraLayoutSpace

added in version 1.0.0
protected int getExtraLayoutSpace (RecyclerView.State state)

Returns the amount of extra space that should be laid out by LayoutManager.

By default, LinearLayoutManager lays out 1 extra page of items while smooth scrolling and 0 otherwise. You can override this method to implement your custom layout pre-cache logic.

Note:Laying out invisible elements generally comes with significant performance cost. It's typically only desirable in places like smooth scrolling to an unknown location, where 1) the extra content helps LinearLayoutManager know in advance when its target is approaching, so it can decelerate early and smoothly and 2) while motion is continuous.

Extending the extra layout space is especially expensive if done while the user may change scrolling direction. Changing direction will cause the extra layout space to swap to the opposite side of the viewport, incurring many rebinds/recycles, unless the cache is large enough to handle it.

Parameters
state RecyclerView.State

Returns
int The extra space that should be laid out (in pixels).

isLayoutRTL

added in version 1.0.0
protected boolean isLayoutRTL ()

Returns
boolean