Android APIs
public static abstract class

RecyclerView.LayoutManager

extends Object
java.lang.Object
   ↳ android.support.v7.widget.RecyclerView.LayoutManager
Known Direct Subclasses

Class Overview

A LayoutManager is responsible for measuring and positioning item views within a RecyclerView as well as determining the policy for when to recycle item views that are no longer visible to the user. By changing the LayoutManager a RecyclerView can be used to implement a standard vertically scrolling list, a uniform grid, staggered grids, horizontally scrolling collections and more. Several stock layout managers are provided for general use.

Summary

Public Constructors
RecyclerView.LayoutManager()
Public Methods
void addView(View child, int index)
Add a view to the currently attached RecyclerView if needed.
void addView(View child)
Add a view to the currently attached RecyclerView if needed.
void attachView(View child)
Reattach a previously detached view.
void attachView(View child, int index, RecyclerView.LayoutParams lp)
Reattach a previously detached view.
void attachView(View child, int index)
Reattach a previously detached view.
boolean canScrollHorizontally()
Query if horizontal scrolling is currently supported.
boolean canScrollVertically()
Query if vertical scrolling is currently supported.
boolean checkLayoutParams(RecyclerView.LayoutParams lp)
Determines the validity of the supplied LayoutParams object.
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.

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.

void detachAndScrapAttachedViews(RecyclerView.Recycler recycler)
Temporarily detach and scrap all currently attached child views.
void detachAndScrapView(View child, RecyclerView.Recycler recycler)
Detach a child view and add it to a Recycler's scrap heap.
void detachAndScrapViewAt(int index, RecyclerView.Recycler recycler)
Detach a child view and add it to a Recycler's scrap heap.
void detachView(View child)
Temporarily detach a child view.
void detachViewAt(int index)
Temporarily detach a child view.
View findViewByPosition(int position)

Finds the view which represents the given adapter position.

abstract RecyclerView.LayoutParams generateDefaultLayoutParams()
Create a default LayoutParams object for a child of the RecyclerView.
RecyclerView.LayoutParams generateLayoutParams(ViewGroup.LayoutParams lp)
Create a LayoutParams object suitable for this LayoutManager, copying relevant values from the supplied LayoutParams object if possible.
RecyclerView.LayoutParams generateLayoutParams(Context c, AttributeSet attrs)
Create a LayoutParams object suitable for this LayoutManager from an inflated layout resource.
View getChildAt(int index)
Return the child view at the given index
int getChildCount()
Return the current number of child views attached to the parent RecyclerView.
static int getChildMeasureSpec(int parentSize, int padding, int childDimension, boolean canScroll)
Calculate a MeasureSpec value for measuring a child view in one dimension.
int getDecoratedBottom(View child)
Returns the bottom edge of the given child view within its parent, offset by any applied ItemDecorations.
int getDecoratedLeft(View child)
Returns the left edge of the given child view within its parent, offset by any applied ItemDecorations.
int getDecoratedMeasuredHeight(View child)
Returns the measured height of the given child, plus the additional size of any insets applied by ItemDecorations.
int getDecoratedMeasuredWidth(View child)
Returns the measured width of the given child, plus the additional size of any insets applied by ItemDecorations.
int getDecoratedRight(View child)
Returns the right edge of the given child view within its parent, offset by any applied ItemDecorations.
int getDecoratedTop(View child)
Returns the top edge of the given child view within its parent, offset by any applied ItemDecorations.
int getHeight()
Return the height of the parent RecyclerView
int getItemCount()
Return the number of items in the adapter bound to the parent RecyclerView
int getLayoutDirection()
Returns the resolved layout direction for this RecyclerView.
int getMinimumHeight()
int getMinimumWidth()
int getPaddingBottom()
Return the bottom padding of the parent RecyclerView
int getPaddingEnd()
Return the end padding of the parent RecyclerView
int getPaddingLeft()
Return the left padding of the parent RecyclerView
int getPaddingRight()
Return the right padding of the parent RecyclerView
int getPaddingStart()
Return the start padding of the parent RecyclerView
int getPaddingTop()
Return the top padding of the parent RecyclerView
int getPosition(View view)
Returns the adapter position of the item represented by the given View.
int getWidth()
Return the width of the parent RecyclerView
boolean hasFocus()
Returns true if the RecyclerView this LayoutManager is bound to has or contains focus.
boolean isFocused()
Returns true if the RecyclerView this LayoutManager is bound to has focus.
boolean isSmoothScrolling()
void layoutDecorated(View child, int left, int top, int right, int bottom)
Lay out the given child view within the RecyclerView using coordinates that include any current ItemDecorations.
void measureChild(View child, int widthUsed, int heightUsed)
Measure a child view using standard measurement policy, taking the padding of the parent RecyclerView and any added item decorations into account.
void measureChildWithMargins(View child, int widthUsed, int heightUsed)
Measure a child view using standard measurement policy, taking the padding of the parent RecyclerView, any added item decorations and the child margins into account.
void offsetChildrenHorizontal(int dx)
Offset all child views attached to the parent RecyclerView by dx pixels along the horizontal axis.
void offsetChildrenVertical(int dy)
Offset all child views attached to the parent RecyclerView by dy pixels along the vertical axis.
void onAdapterChanged(Adapter oldAdapter, Adapter newAdapter)
Called if the RecyclerView this LayoutManager is bound to has a different adapter set.
boolean onAddFocusables(RecyclerView recyclerView, ArrayList<View> views, int direction, int focusableMode)
Called to populate focusable views within the RecyclerView.
void onAttachedToWindow(RecyclerView view)
Called when this LayoutManager is both attached to a RecyclerView and that RecyclerView is attached to a window.
void onDetachedFromWindow(RecyclerView view)
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 direction, 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.
View onInterceptFocusSearch(View focused, int direction)
This method gives a LayoutManager an opportunity to intercept the initial focus search before the default behavior of FocusFinder is used.
void onItemsAdded(RecyclerView recyclerView, int positionStart, int itemCount)
Called when items have been added to the adapter.
void onItemsRemoved(RecyclerView recyclerView, int positionStart, int itemCount)
Called when items have been removed from the adapter.
void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state)
Lay out all relevant child views from the given adapter.
void onMeasure(RecyclerView.Recycler recycler, RecyclerView.State state, int widthSpec, int heightSpec)
Measure the attached RecyclerView.
boolean onRequestChildFocus(RecyclerView parent, View child, View focused)
Called when a descendant view of the RecyclerView requests focus.
void onRestoreInstanceState(Parcelable state)
Parcelable onSaveInstanceState()

Called when the LayoutManager should save its state.

void removeAllViews()
Remove all views from the currently attached RecyclerView.
void removeAndRecycleView(View child, RecyclerView.Recycler recycler)
Remove a child view and recycle it using the given Recycler.
void removeAndRecycleViewAt(int index, RecyclerView.Recycler recycler)
Remove a child view and recycle it using the given Recycler.
void removeDetachedView(View child)
Finish removing a view that was previously temporarily detached.
void removeView(View child)
Remove a view from the currently attached RecyclerView if needed.
void removeViewAt(int index)
Remove a view from the currently attached RecyclerView if needed.
boolean requestChildRectangleOnScreen(RecyclerView parent, View child, Rect rect, boolean immediate)
Called when a child of the RecyclerView wants a particular rectangle to be positioned onto the screen.
void requestLayout()
Calls RecyclerView#requestLayout on the underlying RecyclerView
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 to the specified adapter position.
int scrollVerticallyBy(int dy, RecyclerView.Recycler recycler, RecyclerView.State state)
Scroll vertically by dy pixels in screen coordinates and return the distance traveled.
void setMeasuredDimension(int widthSize, int heightSize)
Set the measured dimensions of the host RecyclerView.
void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state, int position)

Smooth scroll to the specified adapter position.

void startSmoothScroll(RecyclerView.SmoothScroller smoothScroller)

Starts a smooth scroll using the provided SmoothScroller.

boolean supportsPredictiveItemAnimations()
Returns whether this LayoutManager supports automatic item animations.
[Expand]
Inherited Methods
From class java.lang.Object

Public Constructors

public RecyclerView.LayoutManager ()

Public Methods

public void addView (View child, int index)

Add a view to the currently attached RecyclerView if needed. LayoutManagers should use this method to add views obtained from a RecyclerView.Recycler using getViewForPosition(int).

Parameters
child View to add
index Index to add child at

public void addView (View child)

Add a view to the currently attached RecyclerView if needed. LayoutManagers should use this method to add views obtained from a RecyclerView.Recycler using getViewForPosition(int).

Parameters
child View to add

public void attachView (View child)

Reattach a previously detached view. This method should not be used to reattach views that were previously detachAndScrapView(android.view.View, RecyclerView.Recycler) scrapped}.

Parameters
child Child to reattach

public void attachView (View child, int index, RecyclerView.LayoutParams lp)

Reattach a previously detached view. This method should not be used to reattach views that were previously detachAndScrapView(android.view.View, RecyclerView.Recycler) scrapped}.

Parameters
child Child to reattach
index Intended child index for child
lp LayoutParams for child

public void attachView (View child, int index)

Reattach a previously detached view. This method should not be used to reattach views that were previously detachAndScrapView(android.view.View, RecyclerView.Recycler) scrapped}.

Parameters
child Child to reattach
index Intended child index for child

public boolean canScrollHorizontally ()

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

Returns
  • True if this LayoutManager can scroll the current contents horizontally

public boolean canScrollVertically ()

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

Returns
  • True if this LayoutManager can scroll the current contents vertically

public boolean checkLayoutParams (RecyclerView.LayoutParams lp)

Determines the validity of the supplied LayoutParams object.

This should check to make sure that the object is of the correct type and all values are within acceptable ranges. The default implementation returns true for non-null params.

Parameters
lp LayoutParams object to check
Returns
  • true if this LayoutParams object is valid, false otherwise

public int computeHorizontalScrollExtent (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read computeHorizontalScrollExtent() for details.

Default implementation returns 0.

Parameters
state Current state of RecyclerView
Returns
  • The horizontal extent of the scrollbar's thumb

public int computeHorizontalScrollOffset (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read computeHorizontalScrollOffset() for details.

Default implementation returns 0.

Parameters
state Current State of RecyclerView where you can find total item count
Returns
  • The horizontal offset of the scrollbar's thumb

public int computeHorizontalScrollRange (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read computeHorizontalScrollRange() for details.

Default implementation returns 0.

Parameters
state Current State of RecyclerView where you can find total item count
Returns
  • The total horizontal range represented by the vertical scrollbar

public int computeVerticalScrollExtent (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read computeVerticalScrollExtent() for details.

Default implementation returns 0.

Parameters
state Current state of RecyclerView
Returns
  • The vertical extent of the scrollbar's thumb

public int computeVerticalScrollOffset (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read computeVerticalScrollOffset() for details.

Default implementation returns 0.

Parameters
state Current State of RecyclerView where you can find total item count
Returns
  • The vertical offset of the scrollbar's thumb

public int computeVerticalScrollRange (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read computeVerticalScrollRange() for details.

Default implementation returns 0.

Parameters
state Current State of RecyclerView where you can find total item count
Returns
  • The total vertical range represented by the vertical scrollbar

public void detachAndScrapAttachedViews (RecyclerView.Recycler recycler)

Temporarily detach and scrap all currently attached child views. Views will be scrapped into the given Recycler. The Recycler may prefer to reuse scrap views before other views that were previously recycled.

Parameters
recycler Recycler to scrap views into

public void detachAndScrapView (View child, RecyclerView.Recycler recycler)

Detach a child view and add it to a Recycler's scrap heap.

Scrapping a view allows it to be rebound and reused to show updated or different data.

Parameters
child Child to detach and scrap
recycler Recycler to deposit the new scrap view into

public void detachAndScrapViewAt (int index, RecyclerView.Recycler recycler)

Detach a child view and add it to a Recycler's scrap heap.

Scrapping a view allows it to be rebound and reused to show updated or different data.

Parameters
index Index of child to detach and scrap
recycler Recycler to deposit the new scrap view into

public void detachView (View child)

Temporarily detach a child view.

LayoutManagers may want to perform a lightweight detach operation to rearrange views currently attached to the RecyclerView. Generally LayoutManager implementations will want to use detachAndScrapView(android.view.View, RecyclerView.Recycler) so that the detached view may be rebound and reused.

If a LayoutManager uses this method to detach a view, it must reattach or fully remove the detached view before the LayoutManager entry point method called by RecyclerView returns.

Parameters
child Child to detach

public void detachViewAt (int index)

Temporarily detach a child view.

LayoutManagers may want to perform a lightweight detach operation to rearrange views currently attached to the RecyclerView. Generally LayoutManager implementations will want to use detachAndScrapView(android.view.View, RecyclerView.Recycler) so that the detached view may be rebound and reused.

If a LayoutManager uses this method to detach a view, it must reattach or fully remove the detached view before the LayoutManager entry point method called by RecyclerView returns.

Parameters
index Index of the child to detach

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.

Parameters
position Position of the item in adapter
Returns
  • The child view that represents the given position or null if the position is not visible

public abstract 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
  • A new LayoutParams for a child view

public RecyclerView.LayoutParams generateLayoutParams (ViewGroup.LayoutParams lp)

Create a LayoutParams object suitable for this LayoutManager, copying relevant values from the supplied LayoutParams object if possible.

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).

Parameters
lp Source LayoutParams object to copy values from
Returns
  • a new LayoutParams object

public RecyclerView.LayoutParams generateLayoutParams (Context c, AttributeSet attrs)

Create a LayoutParams object suitable for this LayoutManager from an inflated layout resource.

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).

Parameters
c Context for obtaining styled attributes
attrs AttributeSet describing the supplied arguments
Returns
  • a new LayoutParams object

public View getChildAt (int index)

Return the child view at the given index

Parameters
index Index of child to return
Returns
  • Child view at index

public int getChildCount ()

Return the current number of child views attached to the parent RecyclerView. This does not include child views that were temporarily detached and/or scrapped.

Returns
  • Number of attached children

public static int getChildMeasureSpec (int parentSize, int padding, int childDimension, boolean canScroll)

Calculate a MeasureSpec value for measuring a child view in one dimension.

Parameters
parentSize Size of the parent view where the child will be placed
padding Total space currently consumed by other elements of parent
childDimension Desired size of the child view, or MATCH_PARENT/WRAP_CONTENT. Generally obtained from the child view's LayoutParams
canScroll true if the parent RecyclerView can scroll in this dimension
Returns
  • a MeasureSpec value for the child view

public int getDecoratedBottom (View child)

Returns the bottom edge of the given child view within its parent, offset by any applied ItemDecorations.

Parameters
child Child to query
Returns
  • Child bottom edge with offsets applied

public int getDecoratedLeft (View child)

Returns the left edge of the given child view within its parent, offset by any applied ItemDecorations.

Parameters
child Child to query
Returns
  • Child left edge with offsets applied

public int getDecoratedMeasuredHeight (View child)

Returns the measured height of the given child, plus the additional size of any insets applied by ItemDecorations.

Parameters
child Child view to query
Returns
  • child's measured height plus ItemDecoration insets

public int getDecoratedMeasuredWidth (View child)

Returns the measured width of the given child, plus the additional size of any insets applied by ItemDecorations.

Parameters
child Child view to query
Returns
  • child's measured width plus ItemDecoration insets

public int getDecoratedRight (View child)

Returns the right edge of the given child view within its parent, offset by any applied ItemDecorations.

Parameters
child Child to query
Returns
  • Child right edge with offsets applied

public int getDecoratedTop (View child)

Returns the top edge of the given child view within its parent, offset by any applied ItemDecorations.

Parameters
child Child to query
Returns
  • Child top edge with offsets applied

public int getHeight ()

Return the height of the parent RecyclerView

Returns
  • Height in pixels

public int getItemCount ()

Return the number of items in the adapter bound to the parent RecyclerView

Returns
  • Items in the bound adapter

public int getLayoutDirection ()

Returns the resolved layout direction for this RecyclerView.

Returns

public int getMinimumHeight ()

Returns

public int getMinimumWidth ()

Returns

public int getPaddingBottom ()

Return the bottom padding of the parent RecyclerView

Returns
  • Padding in pixels

public int getPaddingEnd ()

Return the end padding of the parent RecyclerView

Returns
  • Padding in pixels

public int getPaddingLeft ()

Return the left padding of the parent RecyclerView

Returns
  • Padding in pixels

public int getPaddingRight ()

Return the right padding of the parent RecyclerView

Returns
  • Padding in pixels

public int getPaddingStart ()

Return the start padding of the parent RecyclerView

Returns
  • Padding in pixels

public int getPaddingTop ()

Return the top padding of the parent RecyclerView

Returns
  • Padding in pixels

public int getPosition (View view)

Returns the adapter position of the item represented by the given View.

Parameters
view The view to query
Returns
  • The adapter position of the item which is rendered by this View.

public int getWidth ()

Return the width of the parent RecyclerView

Returns
  • Width in pixels

public boolean hasFocus ()

Returns true if the RecyclerView this LayoutManager is bound to has or contains focus.

Returns
  • true if the RecyclerView has or contains focus
See Also

public boolean isFocused ()

Returns true if the RecyclerView this LayoutManager is bound to has focus.

Returns
  • True if the RecyclerView has focus, false otherwise.
See Also

public boolean isSmoothScrolling ()

Returns
  • true if RecycylerView is currently in the state of smooth scrolling.

public void layoutDecorated (View child, int left, int top, int right, int bottom)

Lay out the given child view within the RecyclerView using coordinates that include any current ItemDecorations.

LayoutManagers should prefer working in sizes and coordinates that include item decoration insets whenever possible. This allows the LayoutManager to effectively ignore decoration insets within measurement and layout code. See the following methods:

Parameters
child Child to lay out
left Left edge, with item decoration insets included
top Top edge, with item decoration insets included
right Right edge, with item decoration insets included
bottom Bottom edge, with item decoration insets included

public void measureChild (View child, int widthUsed, int heightUsed)

Measure a child view using standard measurement policy, taking the padding of the parent RecyclerView and any added item decorations into account.

If the RecyclerView can be scrolled in either dimension the caller may pass 0 as the widthUsed or heightUsed parameters as they will be irrelevant.

Parameters
child Child view to measure
widthUsed Width in pixels currently consumed by other views, if relevant
heightUsed Height in pixels currently consumed by other views, if relevant

public void measureChildWithMargins (View child, int widthUsed, int heightUsed)

Measure a child view using standard measurement policy, taking the padding of the parent RecyclerView, any added item decorations and the child margins into account.

If the RecyclerView can be scrolled in either dimension the caller may pass 0 as the widthUsed or heightUsed parameters as they will be irrelevant.

Parameters
child Child view to measure
widthUsed Width in pixels currently consumed by other views, if relevant
heightUsed Height in pixels currently consumed by other views, if relevant

public void offsetChildrenHorizontal (int dx)

Offset all child views attached to the parent RecyclerView by dx pixels along the horizontal axis.

Parameters
dx Pixels to offset by

public void offsetChildrenVertical (int dy)

Offset all child views attached to the parent RecyclerView by dy pixels along the vertical axis.

Parameters
dy Pixels to offset by

public void onAdapterChanged (Adapter oldAdapter, Adapter newAdapter)

Called if the RecyclerView this LayoutManager is bound to has a different adapter set. The LayoutManager may use this opportunity to clear caches and configure state such that it can relayout appropriately with the new data and potentially new view types.

The default implementation removes all currently attached views.

Parameters
oldAdapter The previous adapter instance. Will be null if there was previously no adapter.
newAdapter The new adapter instance. Might be null if setAdapter(RecyclerView.Adapter) is called with null.

public boolean onAddFocusables (RecyclerView recyclerView, ArrayList<View> views, int direction, int focusableMode)

Called to populate focusable views within the RecyclerView.

The LayoutManager implementation should return true if the default behavior of addFocusables(java.util.ArrayList, int) should be suppressed.

The default implementation returns false to trigger RecyclerView to fall back to the default ViewGroup behavior.

Parameters
recyclerView The RecyclerView hosting this LayoutManager
views List of output views. This method should add valid focusable views to this list.
direction One of FOCUS_UP, FOCUS_DOWN, FOCUS_LEFT, FOCUS_RIGHT, FOCUS_BACKWARD, FOCUS_FORWARD
focusableMode The type of focusables to be added.
Returns
  • true to suppress the default behavior, false to add default focusables after this method returns.

public void onAttachedToWindow (RecyclerView view)

Called when this LayoutManager is both attached to a RecyclerView and that RecyclerView is attached to a window.

Subclass implementations should always call through to the superclass implementation.

Parameters
view The RecyclerView this LayoutManager is bound to

public void onDetachedFromWindow (RecyclerView view)

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

Subclass implementations should always call through to the superclass implementation.

Parameters
view The RecyclerView this LayoutManager is bound to

public View onFocusSearchFailed (View focused, int direction, 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. The default implementation returns null.

Parameters
focused The currently focused view
direction One of FOCUS_UP, FOCUS_DOWN, FOCUS_LEFT, FOCUS_RIGHT, FOCUS_BACKWARD, FOCUS_FORWARD or 0 for not applicable
recycler The recycler to use for obtaining views for currently offscreen items
state Transient state of RecyclerView
Returns
  • The chosen view to be focused

public View onInterceptFocusSearch (View focused, int direction)

This method gives a LayoutManager an opportunity to intercept the initial focus search before the default behavior of FocusFinder is used. If this method returns null FocusFinder will attempt to find a focusable child view. If it fails then onFocusSearchFailed(View, int, RecyclerView.Recycler, RecyclerView.State) will be called to give the LayoutManager an opportunity to add new views for items that did not have attached views representing them. The LayoutManager should not add or remove views from this method.

Parameters
focused The currently focused view
direction One of FOCUS_UP, FOCUS_DOWN, FOCUS_LEFT, FOCUS_RIGHT, FOCUS_BACKWARD, FOCUS_FORWARD
Returns
  • A descendant view to focus or null to fall back to default behavior. The default implementation returns null.

public void onItemsAdded (RecyclerView recyclerView, int positionStart, int itemCount)

Called when items have been added to the adapter. The LayoutManager may choose to requestLayout if the inserted items would require refreshing the currently visible set of child views. (e.g. currently empty space would be filled by appended items, etc.)

public void onItemsRemoved (RecyclerView recyclerView, int positionStart, int itemCount)

Called when items have been removed from the adapter.

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 simple fade views in and out, whether they are actuall 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 Recycler to use for fetching potentially cached views for a position
state Transient state of RecyclerView

public void onMeasure (RecyclerView.Recycler recycler, RecyclerView.State state, int widthSpec, int heightSpec)

Measure the attached RecyclerView. Implementations must call setMeasuredDimension(int, int) before returning.

The default implementation will handle EXACTLY measurements and respect the minimum width and height properties of the host RecyclerView if measured as UNSPECIFIED. AT_MOST measurements will be treated as EXACTLY and the RecyclerView will consume all available space.

Parameters
recycler Recycler
state Transient state of RecyclerView
widthSpec Width View.MeasureSpec
heightSpec Height View.MeasureSpec

public boolean onRequestChildFocus (RecyclerView parent, View child, View focused)

Called when a descendant view of the RecyclerView requests focus.

A LayoutManager wishing to keep focused views aligned in a specific portion of the view may implement that behavior in an override of this method.

If the LayoutManager executes different behavior that should override the default behavior of scrolling the focused child on screen instead of running alongside it, this method should return true.

Parameters
parent The RecyclerView hosting this LayoutManager
child Direct child of the RecyclerView containing the newly focused view
focused The newly focused view. This may be the same view as child
Returns
  • true if the default scroll behavior should be suppressed

public void onRestoreInstanceState (Parcelable state)

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
  • Necessary information for LayoutManager to be able to restore its state

public void removeAllViews ()

Remove all views from the currently attached RecyclerView. This will not recycle any of the affected views; the LayoutManager is responsible for doing so if desired.

public void removeAndRecycleView (View child, RecyclerView.Recycler recycler)

Remove a child view and recycle it using the given Recycler.

Parameters
child Child to remove and recycle
recycler Recycler to use to recycle child

public void removeAndRecycleViewAt (int index, RecyclerView.Recycler recycler)

Remove a child view and recycle it using the given Recycler.

Parameters
index Index of child to remove and recycle
recycler Recycler to use to recycle child

public void removeDetachedView (View child)

Finish removing a view that was previously temporarily detached.

Parameters
child Detached child to remove

public void removeView (View child)

Remove a view from the currently attached RecyclerView if needed. LayoutManagers should use this method to completely remove a child view that is no longer needed. LayoutManagers should strongly consider recycling removed views using recycleView(android.view.View).

Parameters
child View to remove

public void removeViewAt (int index)

Remove a view from the currently attached RecyclerView if needed. LayoutManagers should use this method to completely remove a child view that is no longer needed. LayoutManagers should strongly consider recycling removed views using recycleView(android.view.View).

Parameters
index Index of the child view to remove

public boolean requestChildRectangleOnScreen (RecyclerView parent, View child, Rect rect, boolean immediate)

Called when a child of the RecyclerView wants a particular rectangle to be positioned onto the screen. See requestChildRectangleOnScreen(android.view.View, android.graphics.Rect, boolean) for more details.

The base implementation will attempt to perform a standard programmatic scroll to bring the given rect into view, within the padded area of the RecyclerView.

Parameters
child The direct child making the request.
rect The rectangle in the child's coordinates the child wishes to be on the screen.
immediate True to forbid animated or delayed scrolling, false otherwise
Returns
  • Whether the group scrolled to handle the operation

public void requestLayout ()

Calls RecyclerView#requestLayout on the underlying RecyclerView

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 distance to scroll by in pixels. X increases as scroll position approaches the right.
recycler Recycler to use for fetching potentially cached views for a position
state Transient state of RecyclerView
Returns
  • 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.

public void scrollToPosition (int position)

Scroll to the specified adapter position. Actual position of the item on the screen depends on the LayoutManager implementation.

Parameters
position Scroll to this adapter position.

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 distance to scroll in pixels. Y increases as scroll position approaches the bottom.
recycler Recycler to use for fetching potentially cached views for a position
state Transient state of RecyclerView
Returns
  • 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.

public void setMeasuredDimension (int widthSize, int heightSize)

Set the measured dimensions of the host RecyclerView.

Parameters
widthSize Measured width
heightSize Measured height

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 The RecyclerView to which this layout manager is attached
state Current State of RecyclerView
position Scroll to this adapter position.

public void startSmoothScroll (RecyclerView.SmoothScroller smoothScroller)

Starts a smooth scroll using the provided SmoothScroller.

Calling this method will cancel any previous smooth scroll request.

Parameters
smoothScroller Unstance which defines how smooth scroll should be animated

public boolean supportsPredictiveItemAnimations ()

Returns whether this LayoutManager supports automatic item animations. A LayoutManager wishing to support item animations should obey certain rules as outlined in onLayoutChildren(Recycler, State). The default return value is false, so subclasses of LayoutManager will not get predictive item animations by default.

Whether item animations are enabled in a RecyclerView is determined both by 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 simple item animations will be enabled, in which views that are moving onto or off of the screen are simply faded in/out. If the RecyclerView has a non-null ItemAnimator and this method returns true, then there will be two calls to onLayoutChildren(Recycler, State) to setup up the information needed to more intelligently predict where appearing and disappearing views should be animated from/to.

Returns
  • true if predictive item animations should be enabled, false otherwise