LayoutManager

abstract class LayoutManager
kotlin.Any
   ↳ androidx.recyclerview.widget.RecyclerView.LayoutManager

A LayoutManager is responsible for measuring and positioning item views within a RecyclerView as well as determining the policy for when to recycle item views that are no longer visible to the user. 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.

If the LayoutManager specifies a default constructor or one with the signature (Context, AttributeSet, int, int), RecyclerView will instantiate and set the LayoutManager when being inflated. Most used properties can be then obtained from getProperties(Context, AttributeSet, int, int). In case a LayoutManager specifies both constructors, the non-default constructor will take precedence.

Summary

Nested classes
abstract

Interface for LayoutManagers to request items to be prefetched, based on position, with specified distance from viewport, which indicates priority.
open

Some general properties that a LayoutManager may want to use.

Public constructors

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.

Public methods
open Unit

To be called only during onLayoutChildren(Recycler, State) to add a view to the layout that is known to be going away, either because it has been removed or because it is actually not in the visible portion of the container but is being laid out in order to inform RecyclerView in how to animate the item out of view.
open Unit
addDisappearingView(child: View!, index: Int)

To be called only during onLayoutChildren(Recycler, State) to add a view to the layout that is known to be going away, either because it has been removed or because it is actually not in the visible portion of the container but is being laid out in order to inform RecyclerView in how to animate the item out of view.
open Unit
addView(child: View!)

Add a view to the currently attached RecyclerView if needed.
open Unit
addView(child: View!, index: Int)

Add a view to the currently attached RecyclerView if needed.
open Unit

Checks if RecyclerView is in the middle of a layout or scroll and throws an IllegalStateException if it is not.
open Unit

Checks if RecyclerView is in the middle of a layout or scroll and throws an IllegalStateException if it is.
open Unit
attachView(@NonNull child: View, index: Int, lp: RecyclerView.LayoutParams!)

Reattach a previously detached view.
open Unit
attachView(@NonNull child: View, index: Int)

Reattach a previously detached view.
open Unit
attachView(@NonNull child: View)

Reattach a previously detached view.
open Unit
calculateItemDecorationsForChild(@NonNull child: View, @NonNull outRect: Rect)

Calculates the item decor insets applied to the given child and updates the provided Rect instance with the inset values.
open Boolean

Query if horizontal scrolling is currently supported.
open Boolean

Query if vertical scrolling is currently supported.
open Boolean

Determines the validity of the supplied LayoutParams object.
open static Int
chooseSize(spec: Int, desired: Int, min: Int)

Chooses a size from the given specs and parameters that is closest to the desired size and also complies with the spec.
open Unit

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

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.
open Int

Override this method if you want to support scroll bars.
open Int

Override this method if you want to support scroll bars.
open Int

Override this method if you want to support scroll bars.
open Int

Override this method if you want to support scroll bars.
open Int

Override this method if you want to support scroll bars.
open Int

Override this method if you want to support scroll bars.
open Unit

Temporarily detach and scrap all currently attached child views.
open Unit
detachAndScrapView(@NonNull child: View, @NonNull recycler: RecyclerView.Recycler)

Detach a child view and add it to a Recycler's scrap heap.
open Unit
detachAndScrapViewAt(index: Int, @NonNull recycler: RecyclerView.Recycler)

Detach a child view and add it to a Recycler's scrap heap.
open Unit
detachView(@NonNull child: View)

Temporarily detach a child view.
open Unit
detachViewAt(index: Int)

Temporarily detach a child view.
open Unit

Ends all animations on the view created by the ItemAnimator.
open View?
findContainingItemView(@NonNull view: View)

Traverses the ancestors of the given view and returns the item view that contains it and also a direct child of the LayoutManager.
open View?

Finds the view which represents the given adapter position.
abstract RecyclerView.LayoutParams!

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

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

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

Returns offset of the RecyclerView's text baseline from the its top boundary.
open Int

Returns the total height of item decorations applied to child's bottom.
open View?
getChildAt(index: Int)

Return the child view at the given index
open Int

Return the current number of child views attached to the parent RecyclerView.
open static Int
getChildMeasureSpec(parentSize: Int, padding: Int, childDimension: Int, canScroll: Boolean)

Calculate a MeasureSpec value for measuring a child view in one dimension.
open static Int
getChildMeasureSpec(parentSize: Int, parentMode: Int, padding: Int, childDimension: Int, canScroll: Boolean)

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

Check if the RecyclerView is configured to clip child views to its padding.
open Int

Returns the number of columns for accessibility.
open Int
getDecoratedBottom(@NonNull child: View)

Returns the bottom edge of the given child view within its parent, offset by any applied ItemDecorations.
open Unit
getDecoratedBoundsWithMargins(@NonNull view: View, @NonNull outBounds: Rect)

Returns the bounds of the view including its decoration and margins.
open Int
getDecoratedLeft(@NonNull child: View)

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

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

Returns the measured width of the given child, plus the additional size of any insets applied by ItemDecorations.
open Int
getDecoratedRight(@NonNull child: View)

Returns the right edge of the given child view within its parent, offset by any applied ItemDecorations.
open Int
getDecoratedTop(@NonNull child: View)

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

Returns the item View which has or contains focus.
open Int

Returns the height that is currently relevant to the LayoutManager.
open Int

Return the height measurement spec mode that is currently relevant to the LayoutManager.
open Int

Returns the number of items in the adapter bound to the parent RecyclerView.
open Int
getItemViewType(@NonNull view: View)

Returns the View type defined by the adapter.
open Int

Returns the resolved layout direction for this RecyclerView.
open Int
getLeftDecorationWidth(@NonNull child: View)

Returns the total width of item decorations applied to child's left.
open Int

open Int

open Int

Return the bottom padding of the parent RecyclerView
open Int

Return the end padding of the parent RecyclerView
open Int

Return the left padding of the parent RecyclerView
open Int

Return the right padding of the parent RecyclerView
open Int

Return the start padding of the parent RecyclerView
open Int

Return the top padding of the parent RecyclerView
open Int
getPosition(@NonNull view: View)

Returns the adapter position of the item represented by the given View.
open static RecyclerView.LayoutManager.Properties!
getProperties(@NonNull context: Context, @Nullable attrs: AttributeSet?, defStyleAttr: Int, defStyleRes: Int)

Parse the xml attributes to get the most common properties used by layout managers.
open Int
getRightDecorationWidth(@NonNull child: View)

Returns the total width of item decorations applied to child's right.
open Int

Returns the number of rows for accessibility.
open Int

Returns the selection mode for accessibility.
open Int
getTopDecorationHeight(@NonNull child: View)

Returns the total height of item decorations applied to child's top.
open Unit
getTransformedBoundingBox(@NonNull child: View, includeDecorInsets: Boolean, @NonNull out: Rect)

Calculates the bounding box of the View while taking into account its matrix changes (translation, scale etc) with respect to the RecyclerView.
open Int

Returns the width that is currently relevant to the LayoutManager.
open Int

Return the width measurement spec mode that is currently relevant to the LayoutManager.
open Boolean

Returns true if the RecyclerView this LayoutManager is bound to has or contains focus.
open Unit
ignoreView(@NonNull view: View)

Flags a view so that it will not be scrapped or recycled.
open Boolean

Returns whether LayoutManager is currently attached to a RecyclerView which is attached to a window.
open Boolean

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 LayoutManager#onMeasure(Recycler, State, int, int).
open Boolean

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

Sets whether the LayoutManager should be queried for views outside of its viewport while the UI thread is idle between frames.
open Boolean
isLayoutHierarchical(@NonNull recycler: RecyclerView.Recycler, @NonNull state: RecyclerView.State)

Returns whether layout is hierarchical or not to be used for accessibility.
open Boolean

In addition to the View Framework's measurement cache, RecyclerView uses its own additional measurement cache for its children to avoid re-measuring them when not necessary.
open Boolean

open Boolean
isViewPartiallyVisible(@NonNull child: View, completelyVisible: Boolean, acceptEndPointInclusion: Boolean)

Returns whether the given child view is partially or fully visible within the padded bounded area of RecyclerView, depending on the input parameters.
open Unit
layoutDecorated(@NonNull child: View, left: Int, top: Int, right: Int, bottom: Int)

Lay out the given child view within the RecyclerView using coordinates that include any current ItemDecorations.
open Unit
layoutDecoratedWithMargins(@NonNull child: View, left: Int, top: Int, right: Int, bottom: Int)

Lay out the given child view within the RecyclerView using coordinates that include any current ItemDecorations and margins.
open Unit
measureChild(@NonNull child: View, widthUsed: Int, heightUsed: Int)

Measure a child view using standard measurement policy, taking the padding of the parent RecyclerView and any added item decorations into account.
open Unit
measureChildWithMargins(@NonNull child: View, widthUsed: Int, heightUsed: Int)

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.
open Unit
moveView(fromIndex: Int, toIndex: Int)

Moves a View from one position to another.
open Unit

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

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

Called if the RecyclerView this LayoutManager is bound to has a different adapter set via RecyclerView#setAdapter(Adapter) or RecyclerView#swapAdapter(Adapter, boolean).
open Boolean
onAddFocusables(@NonNull recyclerView: RecyclerView, @NonNull views: ArrayList<View!>, direction: Int, focusableMode: Int)

Called to populate focusable views within the RecyclerView.
open Unit

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

open Unit

Called when this LayoutManager is detached from its parent RecyclerView or when its parent RecyclerView is detached from its window.
open View?
onFocusSearchFailed(@NonNull focused: View, direction: Int, @NonNull recycler: RecyclerView.Recycler, @NonNull state: RecyclerView.State)

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

open Unit
onInitializeAccessibilityEvent(@NonNull recycler: RecyclerView.Recycler, @NonNull state: RecyclerView.State, @NonNull event: AccessibilityEvent)

Called by the accessibility delegate to initialize an accessibility event.
open Unit

Called by the AccessibilityDelegate when the information about the current layout should be populated.
open Unit
onInitializeAccessibilityNodeInfoForItem(@NonNull recycler: RecyclerView.Recycler, @NonNull state: RecyclerView.State, @NonNull host: View, @NonNull info: AccessibilityNodeInfoCompat)

Called by the AccessibilityDelegate when the accessibility information for a specific item should be populated.
open View?
onInterceptFocusSearch(@NonNull focused: View, direction: Int)

This method gives a LayoutManager an opportunity to intercept the initial focus search before the default behavior of FocusFinder is used.
open Unit
onItemsAdded(@NonNull recyclerView: RecyclerView, positionStart: Int, itemCount: Int)

Called when items have been added to the adapter.
open Unit
onItemsChanged(@NonNull recyclerView: RecyclerView)

Called in response to a call to Adapter#notifyDataSetChanged() or RecyclerView#swapAdapter(Adapter, boolean) ()} and signals that the the entire data set has changed.
open Unit
onItemsMoved(@NonNull recyclerView: RecyclerView, from: Int, to: Int, itemCount: Int)

Called when an item is moved withing the adapter.
open Unit
onItemsRemoved(@NonNull recyclerView: RecyclerView, positionStart: Int, itemCount: Int)

Called when items have been removed from the adapter.
open Unit
onItemsUpdated(@NonNull recyclerView: RecyclerView, positionStart: Int, itemCount: Int)

Called when items have been changed in the adapter.
open Unit
onItemsUpdated(@NonNull recyclerView: RecyclerView, positionStart: Int, itemCount: Int, @Nullable payload: Any?)

Called when items have been changed in the adapter and with optional payload.
open Unit

Lay out all relevant child views from the given adapter.
open Unit

Called after a full layout calculation is finished.
open Unit
onMeasure(@NonNull recycler: RecyclerView.Recycler, @NonNull state: RecyclerView.State, widthSpec: Int, heightSpec: Int)

Measure the attached RecyclerView.
open Boolean
onRequestChildFocus(@NonNull parent: RecyclerView, @NonNull child: View, @Nullable focused: View?)
open Boolean
onRequestChildFocus(@NonNull parent: RecyclerView, @NonNull state: RecyclerView.State, @NonNull child: View, @Nullable focused: View?)

Called when a descendant view of the RecyclerView requests focus.
open Unit

open Parcelable?

Called when the LayoutManager should save its state.
open Unit

RecyclerView calls this method to notify LayoutManager that scroll state has changed.
open Boolean
performAccessibilityAction(@NonNull recycler: RecyclerView.Recycler, @NonNull state: RecyclerView.State, action: Int, @Nullable args: Bundle?)

Called by AccessibilityDelegate when an action is requested from the RecyclerView.
open Boolean
performAccessibilityActionForItem(@NonNull recycler: RecyclerView.Recycler, @NonNull state: RecyclerView.State, @NonNull view: View, action: Int, @Nullable args: Bundle?)

Called by AccessibilityDelegate when an accessibility action is requested on one of the children of LayoutManager.
open Unit

Causes the Runnable to execute on the next animation time step.
open Unit

Remove all views from the currently attached RecyclerView.
open Unit

Removes all views and recycles them using the given recycler.
open Unit
removeAndRecycleView(@NonNull child: View, @NonNull recycler: RecyclerView.Recycler)

Remove a child view and recycle it using the given Recycler.
open Unit
removeAndRecycleViewAt(index: Int, @NonNull recycler: RecyclerView.Recycler)

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

Removes the specified Runnable from the message queue.
open Unit
removeDetachedView(@NonNull child: View)

Finish removing a view that was previously temporarily detached.
open Unit
removeView(child: View!)

Remove a view from the currently attached RecyclerView if needed.
open Unit
removeViewAt(index: Int)

Remove a view from the currently attached RecyclerView if needed.
open Boolean
requestChildRectangleOnScreen(@NonNull parent: RecyclerView, @NonNull child: View, @NonNull rect: Rect, immediate: Boolean)

Called when a child of the RecyclerView wants a particular rectangle to be positioned onto the screen.
open Boolean
requestChildRectangleOnScreen(@NonNull parent: RecyclerView, @NonNull child: View, @NonNull rect: Rect, immediate: Boolean, focusedChildVisible: Boolean)

Requests that the given child of the RecyclerView be positioned onto the screen.
open Unit

Calls RecyclerView#requestLayout on the underlying RecyclerView
open Unit

A LayoutManager can call this method to force RecyclerView to run simple animations in the next layout pass, even if there is not any trigger to do so.
open Int

Scroll horizontally by dx pixels in screen coordinates and return the distance traveled.
open Unit
scrollToPosition(position: Int)

Scroll to the specified adapter position.
open Int

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

Defines 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 LayoutManager#onMeasure(Recycler, State, int, int).
Unit

Sets whether the LayoutManager should be queried for views outside of its viewport while the UI thread is idle between frames.
open Unit
setMeasuredDimension(childrenBounds: Rect!, wSpec: Int, hSpec: Int)

Sets the measured dimensions from the given bounding box of the children and the measurement specs that were passed into RecyclerView#onMeasure(int, int).
open Unit
setMeasuredDimension(widthSize: Int, heightSize: Int)

Set the measured dimensions of the host RecyclerView.
open Unit
setMeasurementCacheEnabled(measurementCacheEnabled: Boolean)

Sets whether RecyclerView should use its own measurement cache for the children.
open Unit
smoothScrollToPosition(recyclerView: RecyclerView!, state: RecyclerView.State!, position: Int)

Smooth scroll to the specified adapter position.
open Unit

Starts a smooth scroll using the provided SmoothScroller.
open Unit
stopIgnoringView(@NonNull view: View)

View can be scrapped and recycled again.
open Boolean

Returns whether this LayoutManager supports "predictive item animations".

Public constructors

<init>

LayoutManager()

A LayoutManager is responsible for measuring and positioning item views within a RecyclerView as well as determining the policy for when to recycle item views that are no longer visible to the user. 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.

If the LayoutManager specifies a default constructor or one with the signature (Context, AttributeSet, int, int), RecyclerView will instantiate and set the LayoutManager when being inflated. Most used properties can be then obtained from getProperties(Context, AttributeSet, int, int). In case a LayoutManager specifies both constructors, the non-default constructor will take precedence.

Public methods

addDisappearingView

open fun addDisappearingView(child: View!): Unit

To be called only during onLayoutChildren(Recycler, State) to add a view to the layout that is known to be going away, either because it has been removed or because it is actually not in the visible portion of the container but is being laid out in order to inform RecyclerView in how to animate the item out of view.

Views added via this method are going to be invisible to LayoutManager after the dispatchLayout pass is complete. They cannot be retrieved via getChildAt(int) or won't be included in getChildCount() method.

Parameters
child View!: View to add and then remove with animation.

addDisappearingView

open fun addDisappearingView(
    child: View!, 
    index: Int
): Unit

To be called only during onLayoutChildren(Recycler, State) to add a view to the layout that is known to be going away, either because it has been removed or because it is actually not in the visible portion of the container but is being laid out in order to inform RecyclerView in how to animate the item out of view.

Views added via this method are going to be invisible to LayoutManager after the dispatchLayout pass is complete. They cannot be retrieved via getChildAt(int) or won't be included in getChildCount() method.

Parameters
child View!: View to add and then remove with animation.
index Int: Index of the view.

addView

open fun addView(child: View!): Unit

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

Parameters
child View!: View to add

addView

open fun addView(
    child: View!, 
    index: Int
): Unit

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

Parameters
child View!: View to add
index Int: Index to add child at

assertInLayoutOrScroll

open fun assertInLayoutOrScroll(message: String!): Unit

Checks if RecyclerView is in the middle of a layout or scroll and throws an IllegalStateException if it is not.

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

assertNotInLayoutOrScroll

open fun assertNotInLayoutOrScroll(message: String!): Unit

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.

attachView

open fun attachView(
    @NonNull child: View, 
    index: Int, 
    lp: RecyclerView.LayoutParams!
): Unit

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 View: Child to reattach
index Int: Intended child index for child
lp RecyclerView.LayoutParams!: LayoutParams for child

attachView

open fun attachView(
    @NonNull child: View, 
    index: Int
): Unit

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 View: Child to reattach
index Int: Intended child index for child

attachView

open fun attachView(@NonNull child: View): Unit

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 View: Child to reattach

calculateItemDecorationsForChild

open fun calculateItemDecorationsForChild(
    @NonNull child: View, 
    @NonNull outRect: Rect
): Unit

Calculates the item decor insets applied to the given child and updates the provided Rect instance with the inset values.

  • The Rect's left is set to the total width of left decorations.
  • The Rect's top is set to the total height of top decorations.
  • The Rect's right is set to the total width of right decorations.
  • The Rect's bottom is set to total height of bottom decorations.

Note that item decorations are automatically calculated when one of the LayoutManager's measure child methods is called. If you need to measure the child with custom specs via View#measure(int, int), you can use this method to get decorations.

Parameters
child View: The child view whose decorations should be calculated
outRect Rect: The Rect to hold result values

canScrollHorizontally

open fun canScrollHorizontally(): Boolean

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

Return
Boolean True if this LayoutManager can scroll the current contents horizontally

canScrollVertically

open fun canScrollVertically(): Boolean

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

Return
Boolean True if this LayoutManager can scroll the current contents vertically

checkLayoutParams

open fun checkLayoutParams(lp: RecyclerView.LayoutParams!): Boolean

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 RecyclerView.LayoutParams!: LayoutParams object to check
Return
Boolean true if this LayoutParams object is valid, false otherwise

chooseSize

open static fun chooseSize(
    spec: Int, 
    desired: Int, 
    min: Int
): Int

Chooses a size from the given specs and parameters that is closest to the desired size and also complies with the spec.

Parameters
spec Int: The measureSpec
desired Int: The preferred measurement
min Int: The minimum value
Return
Int A size that fits to the given specs

collectAdjacentPrefetchPositions

open fun collectAdjacentPrefetchPositions(
    dx: Int, 
    dy: Int, 
    state: RecyclerView.State!, 
    layoutPrefetchRegistry: RecyclerView.LayoutManager.LayoutPrefetchRegistry!
): Unit

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 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

open fun collectInitialPrefetchPositions(
    adapterItemCount: Int, 
    layoutPrefetchRegistry: RecyclerView.LayoutManager.LayoutPrefetchRegistry!
): Unit

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 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

open fun computeHorizontalScrollExtent(@NonNull state: RecyclerView.State): Int

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
Return
Int The horizontal extent of the scrollbar's thumb

computeHorizontalScrollOffset

open fun computeHorizontalScrollOffset(@NonNull state: RecyclerView.State): Int

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
Return
Int The horizontal offset of the scrollbar's thumb

computeHorizontalScrollRange

open fun computeHorizontalScrollRange(@NonNull state: RecyclerView.State): Int

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
Return
Int The total horizontal range represented by the vertical scrollbar

computeVerticalScrollExtent

open fun computeVerticalScrollExtent(@NonNull state: RecyclerView.State): Int

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
Return
Int The vertical extent of the scrollbar's thumb

computeVerticalScrollOffset

open fun computeVerticalScrollOffset(@NonNull state: RecyclerView.State): Int

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
Return
Int The vertical offset of the scrollbar's thumb

computeVerticalScrollRange

open fun computeVerticalScrollRange(@NonNull state: RecyclerView.State): Int

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
Return
Int The total vertical range represented by the vertical scrollbar

detachAndScrapAttachedViews

open fun detachAndScrapAttachedViews(@NonNull recycler: RecyclerView.Recycler): Unit

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 RecyclerView.Recycler: Recycler to scrap views into

detachAndScrapView

open fun detachAndScrapView(
    @NonNull child: View, 
    @NonNull recycler: RecyclerView.Recycler
): Unit

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 View: Child to detach and scrap
recycler RecyclerView.Recycler: Recycler to deposit the new scrap view into

detachAndScrapViewAt

open fun detachAndScrapViewAt(
    index: Int, 
    @NonNull recycler: RecyclerView.Recycler
): Unit

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 Int: Index of child to detach and scrap
recycler RecyclerView.Recycler: Recycler to deposit the new scrap view into

detachView

open fun detachView(@NonNull child: View): Unit

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 View: Child to detach

detachViewAt

open fun detachViewAt(index: Int): Unit

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 Int: Index of the child to detach

endAnimation

open fun endAnimation(view: View!): Unit

Ends all animations on the view created by the ItemAnimator.

Parameters
view View!: The View for which the animations should be ended.

findContainingItemView

@Nullable open fun findContainingItemView(@NonNull view: View): View?

Traverses the ancestors of the given view and returns the item view that contains it and also a direct child of the LayoutManager.

Note that this method may return null if the view is a child of the RecyclerView but not a child of the LayoutManager (e.g. running a disappear animation).

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

findViewByPosition

@Nullable open fun findViewByPosition(position: Int): View?

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

generateDefaultLayoutParams

abstract fun generateDefaultLayoutParams(): RecyclerView.LayoutParams!

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).

Return
RecyclerView.LayoutParams! A new LayoutParams for a child view

generateLayoutParams

open fun generateLayoutParams(lp: LayoutParams!): RecyclerView.LayoutParams!

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 LayoutParams!: Source LayoutParams object to copy values from
Return
RecyclerView.LayoutParams! a new LayoutParams object

generateLayoutParams

open fun generateLayoutParams(
    c: Context!, 
    attrs: AttributeSet!
): RecyclerView.LayoutParams!

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!: Context for obtaining styled attributes
attrs AttributeSet!: AttributeSet describing the supplied arguments
Return
RecyclerView.LayoutParams! a new LayoutParams object

getBaseline

open fun getBaseline(): Int

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

Return
Int The offset of the RecyclerView's text baseline from the its top boundary; -1 if there is no baseline.

getBottomDecorationHeight

open fun getBottomDecorationHeight(@NonNull child: View): Int

Returns the total height of item decorations applied to child's bottom.

Note that this value is not updated until the View is measured or calculateItemDecorationsForChild(View, Rect) is called.

Parameters
child View: Child to query
Return
Int The total height of item decorations applied to the child's bottom.

getChildAt

@Nullable open fun getChildAt(index: Int): View?

Return the child view at the given index

Parameters
index Int: Index of child to return
Return
View? Child view at index

getChildCount

open fun getChildCount(): Int

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.

Return
Int Number of attached children

getChildMeasureSpec

open static fun getChildMeasureSpec(
    parentSize: Int, 
    padding: Int, 
    childDimension: Int, 
    canScroll: Boolean
): Int

Deprecated: use getChildMeasureSpec(int, int, int, int, boolean)

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

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

getChildMeasureSpec

open static fun getChildMeasureSpec(
    parentSize: Int, 
    parentMode: Int, 
    padding: Int, 
    childDimension: Int, 
    canScroll: Boolean
): Int

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

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

getClipToPadding

open fun getClipToPadding(): Boolean

Check if the RecyclerView is configured to clip child views to its padding.

Return
Boolean true if this RecyclerView clips children to its padding, false otherwise

getColumnCountForAccessibility

open fun getColumnCountForAccessibility(
    @NonNull recycler: RecyclerView.Recycler, 
    @NonNull state: RecyclerView.State
): Int

Returns the number of columns for accessibility.

Default implementation returns the number of items in the adapter if LayoutManager supports horizontal scrolling or 1 if LayoutManager does not support horizontal scrolling.

Parameters
recycler RecyclerView.Recycler: The Recycler that can be used to convert view positions into adapter positions
state RecyclerView.State: The current state of RecyclerView
Return
Int The number of rows in LayoutManager for accessibility.

getDecoratedBottom

open fun getDecoratedBottom(@NonNull child: View): Int

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

Parameters
child View: Child to query
Return
Int Child bottom edge with offsets applied

getDecoratedBoundsWithMargins

open fun getDecoratedBoundsWithMargins(
    @NonNull view: View, 
    @NonNull outBounds: Rect
): Unit

Returns the bounds of the view including its decoration and margins.

Parameters
view View: The view element to check
outBounds Rect: A rect that will receive the bounds of the element including its decoration and margins.

getDecoratedLeft

open fun getDecoratedLeft(@NonNull child: View): Int

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

Parameters
child View: Child to query
Return
Int Child left edge with offsets applied

getDecoratedMeasuredHeight

open fun getDecoratedMeasuredHeight(@NonNull child: View): Int

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

Parameters
child View: Child view to query
Return
Int child's measured height plus ItemDecoration insets

getDecoratedMeasuredWidth

open fun getDecoratedMeasuredWidth(@NonNull child: View): Int

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

Parameters
child View: Child view to query
Return
Int child's measured width plus ItemDecoration insets

getDecoratedRight

open fun getDecoratedRight(@NonNull child: View): Int

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

Parameters
child View: Child to query
Return
Int Child right edge with offsets applied

getDecoratedTop

open fun getDecoratedTop(@NonNull child: View): Int

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

Parameters
child View: Child to query
Return
Int Child top edge with offsets applied

getFocusedChild

@Nullable open fun getFocusedChild(): View?

Returns the item View which has or contains focus.

Return
View? A direct child of RecyclerView which has focus or contains the focused child.

getHeight

@Px open fun getHeight(): Int

Returns the height that is currently relevant to the LayoutManager.

This value is usually equal to the laid out height of the RecyclerView but may reflect the current android.view.View.MeasureSpec height if the LayoutManager is using AutoMeasure and the RecyclerView is in the process of measuring. The LayoutManager must always use this method to retrieve the height relevant to it at any given time.

Return
Int Height in pixels

getHeightMode

open fun getHeightMode(): Int

Return the height measurement spec mode that is currently relevant to the LayoutManager.

This value is set only if the LayoutManager opts into the AutoMeasure api via setAutoMeasureEnabled(boolean).

When RecyclerView is running a layout, this value is always set to View.MeasureSpec#EXACTLY even if it was measured with a different spec mode.

Return
Int Height measure spec mode

getItemCount

open fun getItemCount(): Int

Returns the number of items in the adapter bound to the parent RecyclerView.

Note that this number is not necessarily equal to State#getItemCount(). In methods where State is available, you should use State#getItemCount() instead. For more details, check the documentation for State#getItemCount().

Return
Int The number of items in the bound adapter

getItemViewType

open fun getItemViewType(@NonNull view: View): Int

Returns the View type defined by the adapter.

Parameters
view View: The view to query
Return
Int The type of the view assigned by the adapter.

getLayoutDirection

open fun getLayoutDirection(): Int

Returns the resolved layout direction for this RecyclerView.

Return
Int androidx.core.view.ViewCompat#LAYOUT_DIRECTION_RTL if the layout direction is RTL or returns androidx.core.view.ViewCompat#LAYOUT_DIRECTION_LTR if the layout direction is not RTL.

getLeftDecorationWidth

open fun getLeftDecorationWidth(@NonNull child: View): Int

Returns the total width of item decorations applied to child's left.

Note that this value is not updated until the View is measured or calculateItemDecorationsForChild(View, Rect) is called.

Parameters
child View: Child to query
Return
Int The total width of item decorations applied to the child's left.

getMinimumHeight

@Px open fun getMinimumHeight(): Int
Return
Int The host RecyclerView's View#getMinimumHeight()

getMinimumWidth

@Px open fun getMinimumWidth(): Int
Return
Int The host RecyclerView's View#getMinimumWidth()

getPaddingBottom

@Px open fun getPaddingBottom(): Int

Return the bottom padding of the parent RecyclerView

Return
Int Padding in pixels

getPaddingEnd

@Px open fun getPaddingEnd(): Int

Return the end padding of the parent RecyclerView

Return
Int Padding in pixels

getPaddingLeft

@Px open fun getPaddingLeft(): Int

Return the left padding of the parent RecyclerView

Return
Int Padding in pixels

getPaddingRight

@Px open fun getPaddingRight(): Int

Return the right padding of the parent RecyclerView

Return
Int Padding in pixels

getPaddingStart

@Px open fun getPaddingStart(): Int

Return the start padding of the parent RecyclerView

Return
Int Padding in pixels

getPaddingTop

@Px open fun getPaddingTop(): Int

Return the top padding of the parent RecyclerView

Return
Int Padding in pixels

getPosition

open fun getPosition(@NonNull view: View): Int

Returns the adapter position of the item represented by the given View. This does not contain any adapter changes that might have happened after the last layout.

Parameters
view View: The view to query
Return
Int The adapter position of the item which is rendered by this View.

getProperties

open static fun getProperties(
    @NonNull context: Context, 
    @Nullable attrs: AttributeSet?, 
    defStyleAttr: Int, 
    defStyleRes: Int
): RecyclerView.LayoutManager.Properties!

Parse the xml attributes to get the most common properties used by layout managers. android.R.attr#orientation androidx.recyclerview.R.attr#spanCount androidx.recyclerview.R.attr#reverseLayout androidx.recyclerview.R.attr#stackFromEnd

Return
RecyclerView.LayoutManager.Properties! an object containing the properties as specified in the attrs.

getRightDecorationWidth

open fun getRightDecorationWidth(@NonNull child: View): Int

Returns the total width of item decorations applied to child's right.

Note that this value is not updated until the View is measured or calculateItemDecorationsForChild(View, Rect) is called.

Parameters
child View: Child to query
Return
Int The total width of item decorations applied to the child's right.

getRowCountForAccessibility

open fun getRowCountForAccessibility(
    @NonNull recycler: RecyclerView.Recycler, 
    @NonNull state: RecyclerView.State
): Int

Returns the number of rows for accessibility.

Default implementation returns the number of items in the adapter if LayoutManager supports vertical scrolling or 1 if LayoutManager does not support vertical scrolling.

Parameters
recycler RecyclerView.Recycler: The Recycler that can be used to convert view positions into adapter positions
state RecyclerView.State: The current state of RecyclerView
Return
Int The number of rows in LayoutManager for accessibility.

getSelectionModeForAccessibility

open fun getSelectionModeForAccessibility(
    @NonNull recycler: RecyclerView.Recycler, 
    @NonNull state: RecyclerView.State
): Int

Returns the selection mode for accessibility. Should be AccessibilityNodeInfoCompat.CollectionInfoCompat#SELECTION_MODE_NONE, AccessibilityNodeInfoCompat.CollectionInfoCompat#SELECTION_MODE_SINGLE or AccessibilityNodeInfoCompat.CollectionInfoCompat#SELECTION_MODE_MULTIPLE.

Default implementation returns AccessibilityNodeInfoCompat.CollectionInfoCompat#SELECTION_MODE_NONE.

Parameters
recycler RecyclerView.Recycler: The Recycler that can be used to convert view positions into adapter positions
state RecyclerView.State: The current state of RecyclerView
Return
Int Selection mode for accessibility. Default implementation returns AccessibilityNodeInfoCompat.CollectionInfoCompat#SELECTION_MODE_NONE.

getTopDecorationHeight

open fun getTopDecorationHeight(@NonNull child: View): Int

Returns the total height of item decorations applied to child's top.

Note that this value is not updated until the View is measured or calculateItemDecorationsForChild(View, Rect) is called.

Parameters
child View: Child to query
Return
Int The total height of item decorations applied to the child's top.

getTransformedBoundingBox

open fun getTransformedBoundingBox(
    @NonNull child: View, 
    includeDecorInsets: Boolean, 
    @NonNull out: Rect
): Unit

Calculates the bounding box of the View while taking into account its matrix changes (translation, scale etc) with respect to the RecyclerView.

If includeDecorInsets is true, they are applied first before applying the View's matrix so that the decor offsets also go through the same transformation.

Parameters
child View: The ItemView whose bounding box should be calculated.
includeDecorInsets Boolean: True if the decor insets should be included in the bounding box
out Rect: The rectangle into which the output will be written.

getWidth

@Px open fun getWidth(): Int

Returns the width that is currently relevant to the LayoutManager.

This value is usually equal to the laid out width of the RecyclerView but may reflect the current android.view.View.MeasureSpec width if the LayoutManager is using AutoMeasure and the RecyclerView is in the process of measuring. The LayoutManager must always use this method to retrieve the width relevant to it at any given time.

Return
Int Width in pixels

getWidthMode

open fun getWidthMode(): Int

Return the width measurement spec mode that is currently relevant to the LayoutManager.

This value is set only if the LayoutManager opts into the AutoMeasure api via setAutoMeasureEnabled(boolean).

When RecyclerView is running a layout, this value is always set to View.MeasureSpec#EXACTLY even if it was measured with a different spec mode.

Return
Int Width measure spec mode

hasFocus

open fun hasFocus(): Boolean

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

Return
Boolean true if the RecyclerView has or contains focus

See Also

ignoreView

open fun ignoreView(@NonNull view: View): Unit

Flags a view so that it will not be scrapped or recycled.

Scope of ignoring a child is strictly restricted to position tracking, scrapping and recyling. Methods like removeAndRecycleAllViews(Recycler) will ignore the child whereas removeAllViews() or offsetChildrenHorizontal(int) will not ignore the child.

Before this child can be recycled again, you have to call stopIgnoringView(View).

You can call this method only if your LayoutManger is in onLayout or onScroll callback.

Parameters
view View: View to ignore.

isAttachedToWindow

open fun isAttachedToWindow(): Boolean

Returns whether LayoutManager is currently attached to a RecyclerView which is attached to a window.

Return
Boolean True if this LayoutManager is controlling a RecyclerView and the RecyclerView is attached to window.

isAutoMeasureEnabled

open fun isAutoMeasureEnabled(): Boolean

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 LayoutManager#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, LayoutManager#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 LayoutManager#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 LayoutManager#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 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 State#isMeasuring() set to true and 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 State#isMeasuring() set to true and 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 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.
Return
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 LayoutManager#onMeasure(Recycler, State, int, int).

isFocused

open fun isFocused(): Boolean

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

Return
Boolean True if the RecyclerView has focus, false otherwise.

See Also

isItemPrefetchEnabled

fun isItemPrefetchEnabled(): Boolean

Sets whether the LayoutManager should be queried for views outside of its viewport while the UI thread is idle between frames.

Return
Boolean true if item prefetch is enabled, false otherwise

isLayoutHierarchical

open fun isLayoutHierarchical(
    @NonNull recycler: RecyclerView.Recycler, 
    @NonNull state: RecyclerView.State
): Boolean

Returns whether layout is hierarchical or not to be used for accessibility.

Default implementation returns false.

Parameters
recycler RecyclerView.Recycler: The Recycler that can be used to convert view positions into adapter positions
state RecyclerView.State: The current state of RecyclerView
Return
Boolean True if layout is hierarchical.

isMeasurementCacheEnabled

open fun isMeasurementCacheEnabled(): Boolean

In addition to the View Framework's measurement cache, RecyclerView uses its own additional measurement cache for its children to avoid re-measuring them when not necessary. It is on by default but it can be turned off via setMeasurementCacheEnabled(boolean).

Return
Boolean True if measurement cache is enabled, false otherwise.

isSmoothScrolling

open fun isSmoothScrolling(): Boolean
Return
Boolean true if RecyclerView is currently in the state of smooth scrolling.

isViewPartiallyVisible

open fun isViewPartiallyVisible(
    @NonNull child: View, 
    completelyVisible: Boolean, 
    acceptEndPointInclusion: Boolean
): Boolean

Returns whether the given child view is partially or fully visible within the padded bounded area of RecyclerView, depending on the input parameters. A view is partially visible if it has non-zero overlap with RV's padded bounded area. If acceptEndPointInclusion flag is set to true, it's also considered partially visible if it's located outside RV's bounds and it's hitting either RV's start or end bounds.

Parameters
child View: The child view to be examined.
completelyVisible Boolean: If true, the method returns true if and only if the child is completely visible. If false, the method returns true if and only if the child is only partially visible (that is it will return false if the child is either completely visible or out of RV's bounds).
acceptEndPointInclusion Boolean: If the view's endpoint intersection with RV's start of end bounds is enough to consider it partially visible, false otherwise.
Return
Boolean True if the given child is partially or fully visible, false otherwise.

layoutDecorated

open fun layoutDecorated(
    @NonNull child: View, 
    left: Int, 
    top: Int, 
    right: Int, 
    bottom: Int
): Unit

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 View: Child to lay out
left Int: Left edge, with item decoration insets included
top Int: Top edge, with item decoration insets included
right Int: Right edge, with item decoration insets included
bottom Int: Bottom edge, with item decoration insets included

layoutDecoratedWithMargins

open fun layoutDecoratedWithMargins(
    @NonNull child: View, 
    left: Int, 
    top: Int, 
    right: Int, 
    bottom: Int
): Unit

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

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 View: Child to lay out
left Int: Left edge, with item decoration insets and left margin included
top Int: Top edge, with item decoration insets and top margin included
right Int: Right edge, with item decoration insets and right margin included
bottom Int: Bottom edge, with item decoration insets and bottom margin included

measureChild

open fun measureChild(
    @NonNull child: View, 
    widthUsed: Int, 
    heightUsed: Int
): Unit

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 View: Child view to measure
widthUsed Int: Width in pixels currently consumed by other views, if relevant
heightUsed Int: Height in pixels currently consumed by other views, if relevant

measureChildWithMargins

open fun measureChildWithMargins(
    @NonNull child: View, 
    widthUsed: Int, 
    heightUsed: Int
): Unit

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 View: Child view to measure
widthUsed Int: Width in pixels currently consumed by other views, if relevant
heightUsed Int: Height in pixels currently consumed by other views, if relevant

moveView

open fun moveView(
    fromIndex: Int, 
    toIndex: Int
): Unit

Moves a View from one position to another.

Parameters
fromIndex Int: The View's initial index
toIndex Int: The View's target index

offsetChildrenHorizontal

open fun offsetChildrenHorizontal(@Px dx: Int): Unit

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

Parameters
dx Int: Pixels to offset by

offsetChildrenVertical

open fun offsetChildrenVertical(@Px dy: Int): Unit

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

Parameters
dy Int: Pixels to offset by

onAdapterChanged

open fun onAdapterChanged(
    @Nullable oldAdapter: RecyclerView.Adapter<RecyclerView.ViewHolder!>?, 
    @Nullable newAdapter: RecyclerView.Adapter<RecyclerView.ViewHolder!>?
): Unit

Called if the RecyclerView this LayoutManager is bound to has a different adapter set via RecyclerView#setAdapter(Adapter) or RecyclerView#swapAdapter(Adapter, boolean). 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 RecyclerView.Adapter<RecyclerView.ViewHolder!>?: The previous adapter instance. Will be null if there was previously no adapter.
newAdapter RecyclerView.Adapter<RecyclerView.ViewHolder!>?: The new adapter instance. Might be null if setAdapter(RecyclerView.Adapter) is called with null.

onAddFocusables

open fun onAddFocusables(
    @NonNull recyclerView: RecyclerView, 
    @NonNull views: ArrayList<View!>, 
    direction: Int, 
    focusableMode: Int
): Boolean

Called to populate focusable views within the RecyclerView.

The LayoutManager implementation should return true if the default behavior of ViewGroup#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 RecyclerView: The RecyclerView hosting this LayoutManager
views ArrayList<View!>: List of output views. This method should add valid focusable views to this list.
direction Int: One of View#FOCUS_UP, View#FOCUS_DOWN, View#FOCUS_LEFT, View#FOCUS_RIGHT, View#FOCUS_BACKWARD, View#FOCUS_FORWARD
focusableMode Int: The type of focusables to be added.
Return
Boolean true to suppress the default behavior, false to add default focusables after this method returns.

onAttachedToWindow

@CallSuper open fun onAttachedToWindow(view: RecyclerView!): Unit

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

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.

Subclass implementations should always call through to the superclass implementation.

Parameters
view RecyclerView!: The RecyclerView this LayoutManager is bound to

onDetachedFromWindow

open fun onDetachedFromWindow(view: RecyclerView!): Unit

Deprecated: override onDetachedFromWindow(RecyclerView, Recycler)

onDetachedFromWindow

@CallSuper open fun onDetachedFromWindow(
    view: RecyclerView!, 
    recycler: RecyclerView.Recycler!
): Unit

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

@Nullable open fun onFocusSearchFailed(
    @NonNull focused: View, 
    direction: Int, 
    @NonNull recycler: RecyclerView.Recycler, 
    @NonNull state: RecyclerView.State
): View?

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
direction 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
Return
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

open fun onInitializeAccessibilityEvent(@NonNull event: AccessibilityEvent): Unit

onInitializeAccessibilityEvent

open fun onInitializeAccessibilityEvent(
    @NonNull recycler: RecyclerView.Recycler, 
    @NonNull state: RecyclerView.State, 
    @NonNull event: AccessibilityEvent
): Unit

Called by the accessibility delegate to