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

Public methods
Boolean

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

open View?

Finds the view which represents the given adapter position.

open Int

Override this method if you want to support scroll bars.

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 Unit
attachView(child: View, index: Int, lp: RecyclerView.LayoutParams!)

Reattach a previously detached view.

open Unit
attachView(child: View, index: Int)

Reattach a previously detached view.

open Unit
attachView(child: View)

Reattach a previously detached view.

open Int

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

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
onItemsAdded(recyclerView: RecyclerView, positionStart: Int, itemCount: Int)

Called when items have been added to the adapter.

open Int

Override this method if you want to support scroll bars.

open Unit

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

open Int

Override this method if you want to support scroll bars.

open Unit
layoutDecorated(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 Int

Return the current number of child views attached to the parent RecyclerView.

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

open Unit

open Unit

Called by the accessibility delegate to initialize an accessibility event.

open Unit

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

open Unit
layoutDecoratedWithMargins(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 Int

Override this method if you want to support scroll bars.

open Int

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

open View?
getChildAt(index: Int)

Return the child view at the given index

open Int

Returns the height that is currently relevant to the LayoutManager.

open Int

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

open Int

Returns the number of rows for accessibility.

open Unit

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

open Int

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

open Unit
removeView(child: View!)

Remove a view from the currently attached RecyclerView if needed.

open Boolean

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

open Int

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

open Int

Override this method if you want to support scroll bars.

open Unit
onItemsRemoved(recyclerView: RecyclerView, positionStart: Int, itemCount: Int)

Called when items have been removed from the adapter.

open Int

Return the start padding of the parent RecyclerView

open Unit

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

open Unit
detachView(child: View)

Temporarily detach a child view.

open Unit

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

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).

open Unit

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

open Unit

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

open Unit

Temporarily detach and scrap all currently attached child views.

open Unit
measureChild(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 Boolean
onAddFocusables(recyclerView: RecyclerView, views: ArrayList<View!>, direction: Int, focusableMode: Int)

Called to populate focusable views within the RecyclerView.

open Unit
scrollToPosition(position: Int)

Scroll to the specified adapter position.

open Int

Override this method if you want to support scroll bars.

open Boolean

open Unit

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

open Int

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

open Int

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

open Boolean

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

open Boolean

Called by AccessibilityDelegate when an action is requested from the RecyclerView.

open Unit

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

open Int

Return the end padding of the parent 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 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 whether LayoutManager is currently attached to a RecyclerView which is attached to a window.

open Boolean

Determines the validity of the supplied LayoutParams object.

open Boolean
isViewPartiallyVisible(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 View?

Returns the item View which has or contains focus.

open Unit

Calls RecyclerView#requestLayout on the underlying RecyclerView

open Unit

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

open Boolean

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

open Unit
onInitializeAccessibilityNodeInfoForItem(recycler: RecyclerView.Recycler, state: RecyclerView.State, host: View, info: AccessibilityNodeInfoCompat)

Called by the AccessibilityDelegate when the accessibility information for a specific item should be populated.

open Unit

Called after a full layout calculation is finished.

open Boolean

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

open Unit
measureChildWithMargins(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 Int

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

open Unit

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

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 Unit
removeViewAt(index: Int)

Remove a view from the currently attached RecyclerView if needed.

open View?
onFocusSearchFailed(focused: View, direction: Int, recycler: RecyclerView.Recycler, 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
getTransformedBoundingBox(child: View, includeDecorInsets: Boolean, 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 Unit
smoothScrollToPosition(recyclerView: RecyclerView!, state: RecyclerView.State!, position: Int)

Smooth scroll to the specified adapter position.

open Unit

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

open Int

Return the right padding of the parent RecyclerView

open Boolean

Removes the specified Runnable from the message queue.

open Int

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

open Boolean

Query if vertical scrolling is currently supported.

open Unit
onMeasure(recycler: RecyclerView.Recycler, state: RecyclerView.State, widthSpec: Int, heightSpec: Int)

Measure the attached RecyclerView.

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

Moves a View from one position to another.

open Boolean
onRequestChildFocus(parent: RecyclerView, child: View, focused: View?)

open Boolean
onRequestChildFocus(parent: RecyclerView, state: RecyclerView.State, child: View, focused: View?)

Called when a descendant view of the RecyclerView requests focus.

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

Returns whether this LayoutManager supports "predictive item animations".

open Unit
onItemsMoved(recyclerView: RecyclerView, from: Int, to: Int, itemCount: Int)

Called when an item is moved withing the adapter.

open Int

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

open Parcelable?

Called when the LayoutManager should save its state.

open Int

Returns the resolved layout direction for this RecyclerView.

open Unit

Remove all views from the currently attached RecyclerView.

Unit

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

open Int

Return the left padding of the parent RecyclerView

open Int

Return the top padding of the parent RecyclerView

open 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 Int

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

open Unit

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

open Int

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

open Unit

Starts a smooth scroll using the provided SmoothScroller.

open Int

Return the bottom padding of the parent RecyclerView

open Int

open Int

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

open View?
onInterceptFocusSearch(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 Int

Returns the selection mode for accessibility.

open Boolean
requestChildRectangleOnScreen(parent: RecyclerView, child: View, rect: Rect, immediate: Boolean)

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

open Boolean
requestChildRectangleOnScreen(parent: RecyclerView, child: View, rect: Rect, immediate: Boolean, focusedChildVisible: Boolean)

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

open Unit

View can be scrapped and recycled again.

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 Unit
setMeasurementCacheEnabled(measurementCacheEnabled: Boolean)

Sets whether RecyclerView should use its own measurement cache for the children.

open Unit
onInitializeAccessibilityNodeInfo(recycler: RecyclerView.Recycler, state: RecyclerView.State, info: AccessibilityNodeInfoCompat)

Called by the AccessibilityDelegate when the information about the current layout should be populated.

open Int

Returns the number of columns for accessibility.

open Unit
detachViewAt(index: Int)

Temporarily detach a child view.

abstract RecyclerView.LayoutParams!

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

open Unit

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

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

Finish removing a view that was previously temporarily detached.

open Unit

Ends all animations on the view created by the ItemAnimator.

open Boolean

Query if horizontal scrolling is currently supported.

open Unit
onItemsUpdated(recyclerView: RecyclerView, positionStart: Int, itemCount: Int)

Called when items have been changed in the adapter.

open Unit
onItemsUpdated(recyclerView: RecyclerView, positionStart: Int, itemCount: Int, payload: Any?)

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

open Unit

open Int

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

open Unit

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

open Int

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

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 Int

Returns the View type defined by the adapter.

open Unit

Removes all views and recycles them using the given recycler.

open Unit

Lay out all relevant child views from the given adapter.

open Int

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

open Int

Returns the width that is currently relevant to the LayoutManager.

open Boolean

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

open Int

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

open Unit

RecyclerView calls this method to notify LayoutManager that scroll state has changed.

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 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 static RecyclerView.LayoutManager.Properties!
getProperties(context: Context, attrs: AttributeSet?, defStyleAttr: Int, defStyleRes: Int)

Parse the xml attributes to get the most common properties used by layout managers.

Public constructors

<init>

LayoutManager()

Public methods

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

findViewByPosition

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

computeVerticalScrollExtent

open fun computeVerticalScrollExtent(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

onAdapterChanged

open fun onAdapterChanged(oldAdapter: RecyclerView.Adapter<RecyclerView.ViewHolder!>?, 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.

attachView

open fun attachView(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 View: Intended child index for child
lp View: LayoutParams for child

attachView

open fun attachView(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 View: Intended child index for child

attachView

open fun attachView(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

getLeftDecorationWidth

open fun getLeftDecorationWidth(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.

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 View!: Index to add child at

onItemsAdded

open fun onItemsAdded(recyclerView: RecyclerView, positionStart: Int, itemCount: Int): Unit

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.)

Parameters
recyclerView RecyclerView:
positionStart RecyclerView:
itemCount RecyclerView:

computeVerticalScrollRange

open fun computeVerticalScrollRange(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

onAttachedToWindow

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

computeHorizontalScrollExtent

open fun computeHorizontalScrollExtent(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

layoutDecorated

open fun layoutDecorated(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 View: Left edge, with item decoration insets included
top View: Top edge, with item decoration insets included
right View: Right edge, with item decoration insets included
bottom View: Bottom edge, with item decoration insets included

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

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 Int: PrefetchRegistry to add prefetch entries into.

getMinimumWidth

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

onInitializeAccessibilityEvent

open fun onInitializeAccessibilityEvent(event: AccessibilityEvent): Unit

onInitializeAccessibilityEvent

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

Called by the accessibility delegate to initialize an accessibility event.

Default implementation adds item count and scroll information to the event.

Parameters
recycler RecyclerView.Recycler: The Recycler that can be used to convert view positions into adapter positions
state RecyclerView.Recycler: The current state of RecyclerView
event RecyclerView.Recycler: The event instance to initialize

detachAndScrapView

open fun detachAndScrapView(child: View, 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 View: Recycler to deposit the new scrap view into

layoutDecoratedWithMargins

open fun layoutDecoratedWithMargins(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 View: Left edge, with item decoration insets and left margin included
top View: Top edge, with item decoration insets and top margin included
right View: Right edge, with item decoration insets and right margin included
bottom View: Bottom edge, with item decoration insets and bottom margin included

computeHorizontalScrollRange

open fun computeHorizontalScrollRange(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

getDecoratedTop

open fun getDecoratedTop(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

getChildAt

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

getHeight

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

scrollHorizontallyBy

open fun scrollHorizontallyBy(dx: Int, recycler: RecyclerView.Recycler!, state: RecyclerView.State!): Int

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

Parameters
dx Int: distance to scroll by in pixels. X increases as scroll position approaches the right.
recycler Int: Recycler to use for fetching potentially cached views for a position
state Int: Transient state of RecyclerView
Return
Int: The actual distance scrolled. The return value will be negative if dx was negative and scrolling proceeeded in that direction. Math.abs(result) may be less than dx if a boundary was reached.

getRowCountForAccessibility

open fun getRowCountForAccessibility(recycler: RecyclerView.Recycler, 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.Recycler: The current state of RecyclerView
Return
Int: The number of rows in LayoutManager for accessibility.

detachAndScrapViewAt

open fun detachAndScrapViewAt(index: Int, 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 Int: Recycler to deposit the new scrap view into

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

removeView

open fun removeView(child: View!): Unit

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 Recycler#recycleView(android.view.View).

Parameters
child View!: View to remove

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

scrollVerticallyBy

open fun scrollVerticallyBy(dy: Int, recycler: RecyclerView.Recycler!, state: RecyclerView.State!): Int

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

Parameters
dy Int: distance to scroll in pixels. Y increases as scroll position approaches the bottom.
recycler Int: Recycler to use for fetching potentially cached views for a position
state Int: Transient state of RecyclerView
Return
Int: The actual distance scrolled. The return value will be negative if dy was negative and scrolling proceeeded in that direction. Math.abs(result) may be less than dy if a boundary was reached.

computeVerticalScrollOffset

open fun computeVerticalScrollOffset(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

onItemsRemoved

open fun onItemsRemoved(recyclerView: RecyclerView, positionStart: Int, itemCount: Int): Unit

Called when items have been removed from the adapter.

Parameters
recyclerView RecyclerView:
positionStart RecyclerView:
itemCount RecyclerView:

getPaddingStart

open fun getPaddingStart(): Int

Return the start padding of the parent RecyclerView

Return
Int: Padding in pixels

calculateItemDecorationsForChild

open fun calculateItemDecorationsForChild(child: View, 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 View: The Rect to hold result values

detachView

open fun detachView(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

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.

setAutoMeasureEnabled

open fun setAutoMeasureEnabled(enabled: Boolean): 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).

Parameters
enabled Boolean: True if layout measurement should be done by the RecyclerView, false if it should be done by this LayoutManager.

offsetChildrenHorizontal

open fun offsetChildrenHorizontal(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

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 Int: State of RecyclerView
layoutPrefetchRegistry Int: PrefetchRegistry to add prefetch entries into.

detachAndScrapAttachedViews

open fun detachAndScrapAttachedViews(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

measureChild

open fun measureChild(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 View: Width in pixels currently consumed by other views, if relevant
heightUsed View: Height in pixels currently consumed by other views, if relevant

onAddFocusables

open fun onAddFocusables(recyclerView: RecyclerView, 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 RecyclerView: List of output views. This method should add valid focusable views to this list.
direction RecyclerView: One of View#FOCUS_UP, View#FOCUS_DOWN, View#FOCUS_LEFT, View#FOCUS_RIGHT, View#FOCUS_BACKWARD, View#FOCUS_FORWARD
focusableMode RecyclerView: The type of focusables to be added.
Return
Boolean: true to suppress the default behavior, false to add default focusables after this method returns.

scrollToPosition

open fun scrollToPosition(position: Int): Unit

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

Parameters
position Int: Scroll to this adapter position.

computeHorizontalScrollOffset

open fun computeHorizontalScrollOffset(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

isSmoothScrolling

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

removeAndRecycleView

open fun removeAndRecycleView(child: View, recycler: RecyclerView.Recycler): Unit

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

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

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

getDecoratedLeft

open fun getDecoratedLeft(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

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

performAccessibilityAction

open fun performAccessibilityAction(recycler: RecyclerView.Recycler, state: RecyclerView.State, action: Int, args: Bundle?): Boolean

Called by AccessibilityDelegate when an action is requested from the RecyclerView.

Parameters
recycler RecyclerView.Recycler: The Recycler that can be used to convert view positions into adapter positions
state RecyclerView.Recycler: The current state of RecyclerView
action RecyclerView.Recycler: The action to perform
args RecyclerView.Recycler: Optional action arguments

getDecoratedBoundsWithMargins

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

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

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

getPaddingEnd

open fun getPaddingEnd(): Int

Return the end padding of the parent RecyclerView

Return
Int: Padding in pixels

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 Context!: AttributeSet describing the supplied arguments
Return
RecyclerView.LayoutParams!: a new LayoutParams object

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).

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.

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

isViewPartiallyVisible

open fun isViewPartiallyVisible(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 View: 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 View: 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.

getFocusedChild

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.

requestLayout

open fun requestLayout(): Unit

Calls RecyclerView#requestLayout on the underlying RecyclerView

removeAndRecycleViewAt

open fun removeAndRecycleViewAt(index: Int, recycler: RecyclerView.Recycler): Unit

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

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

performAccessibilityActionForItem

open fun performAccessibilityActionForItem(recycler: RecyclerView.Recycler, state: RecyclerView.State, view: View, action: Int, args: Bundle?): Boolean

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

Default implementation does not do anything.

Parameters
recycler RecyclerView.Recycler: The Recycler that can be used to convert view positions into adapter positions
state RecyclerView.Recycler: The current state of RecyclerView
view RecyclerView.Recycler: The child view on which the action is performed
action RecyclerView.Recycler: The action to perform
args RecyclerView.Recycler: Optional action arguments
Return
Boolean: true if action is handled

onInitializeAccessibilityNodeInfoForItem

open fun onInitializeAccessibilityNodeInfoForItem(recycler: RecyclerView.Recycler, state: RecyclerView.State, host: View, info: AccessibilityNodeInfoCompat): Unit

Called by the AccessibilityDelegate when the accessibility information for a specific item should be populated.

Default implementation adds basic positioning information about the item.

Parameters
recycler RecyclerView.Recycler: The Recycler that can be used to convert view positions into adapter positions
state RecyclerView.Recycler: The current state of RecyclerView
host RecyclerView.Recycler: The child for which accessibility node info should be populated
info RecyclerView.Recycler: The info to fill out about the item

onLayoutCompleted

open fun onLayoutCompleted(state: RecyclerView.State!): Unit

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

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

Parameters
state RecyclerView.State!: Transient state of RecyclerView

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

measureChildWithMargins

open fun measureChildWithMargins(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 View: Width in pixels currently consumed by other views, if relevant
heightUsed View: Height in pixels currently consumed by other views, if relevant

getPosition

open fun getPosition(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.

postOnAnimation

open fun postOnAnimation(action: Runnable!): Unit

Causes the Runnable to execute on the next animation time step. The runnable will be run on the user interface thread.

Calling this method when LayoutManager is not attached to a RecyclerView has no effect.

Parameters
action Runnable!: The Runnable that will be executed.

See Also

requestSimpleAnimationsInNextLayout

open fun requestSimpleAnimationsInNextLayout(): 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. (e.g. adapter data change).

Note that, calling this method will not guarantee that RecyclerView will run animations at all. For example, if there is not any ItemAnimator set, RecyclerView will not run any animations but will still clear this flag after the layout is complete.

removeViewAt

open fun removeViewAt(index: Int): Unit

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 Recycler#recycleView(android.view.View).

Parameters
index Int: Index of the child view to remove

onFocusSearchFailed

open fun onFocusSearchFailed(focused: View, direction: Int, recycler: RecyclerView.Recycler, 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 View: 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 View: The recycler to use for obtaining views for currently offscreen items
state View: 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.

getTransformedBoundingBox

open fun getTransformedBoundingBox(child: View, includeDecorInsets: Boolean, 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 View: True if the decor insets should be included in the bounding box
out View: The rectangle into which the output will be written.

smoothScrollToPosition

open fun smoothScrollToPosition(recyclerView: RecyclerView!, state: RecyclerView.State!, position: Int): Unit

Smooth scroll to the specified adapter position.

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

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

ignoreView

open fun ignoreView(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.

getPaddingRight

open fun getPaddingRight(): Int

Return the right padding of the parent RecyclerView

Return
Int: Padding in pixels

removeCallbacks

open fun removeCallbacks(action: Runnable!): Boolean

Removes the specified Runnable from the message queue.

Calling this method when LayoutManager is not attached to a RecyclerView has no effect.

Parameters
action Runnable!: The Runnable to remove from the message handling queue
Return
Boolean: true if RecyclerView could ask the Handler to remove the Runnable, false otherwise. When the returned value is true, the Runnable may or may not have been actually removed from the message queue (for instance, if the Runnable was not in the queue already.)

See Also

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.

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

onMeasure

open fun onMeasure(recycler: RecyclerView.Recycler, state: RecyclerView.State, widthSpec: Int, heightSpec: Int): Unit

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

It is strongly advised to use the AutoMeasure mechanism by overriding #isAutoMeasureEnabled() to return true as AutoMeasure handles all the standard measure cases including when the RecyclerView's layout_width or layout_height have been set to wrap_content. If #isAutoMeasureEnabled() is overridden to return true, this method should not be overridden.

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 RecyclerView.Recycler: Recycler
state RecyclerView.Recycler: Transient state of RecyclerView
widthSpec RecyclerView.Recycler: Width android.view.View.MeasureSpec
heightSpec RecyclerView.Recycler: Height android.view.View.MeasureSpec

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

onRequestChildFocus

open fun onRequestChildFocus(parent: RecyclerView, child: View, focused: View?): Boolean

onRequestChildFocus

open fun onRequestChildFocus(parent: RecyclerView, state: RecyclerView.State, child: View, focused: View?): Boolean

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 RecyclerView: The RecyclerView hosting this LayoutManager
state RecyclerView: Current state of RecyclerView
child RecyclerView: Direct child of the RecyclerView containing the newly focused view
focused RecyclerView: The newly focused view. This may be the same view as child or it may be null
Return
Boolean: true if the default scroll behavior should be suppressed

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.

supportsPredictiveItemAnimations

open fun supportsPredictiveItemAnimations(): Boolean

Returns whether this LayoutManager supports "predictive item animations".

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

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

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

Return
Boolean: true if this LayoutManager supports predictive item animations, false otherwise.

onItemsMoved

open fun onItemsMoved(recyclerView: RecyclerView, from: Int, to: Int, itemCount: Int): Unit

Called when an item is moved withing the adapter.

Note that, an item may also change position in response to another ADD/REMOVE/MOVE operation. This callback is only called if and only if Adapter#notifyItemMoved is called.

Parameters
recyclerView RecyclerView:
from RecyclerView:
to RecyclerView:
itemCount RecyclerView:

getDecoratedMeasuredWidth

open fun getDecoratedMeasuredWidth(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

onSaveInstanceState

open fun onSaveInstanceState(): Parcelable?

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.

Return
Parcelable?: Necessary information for LayoutManager to be able to restore its state

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.

removeAllViews

open fun removeAllViews(): Unit

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.

setItemPrefetchEnabled

fun setItemPrefetchEnabled(enabled: Boolean): Unit

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

If enabled, the LayoutManager will be queried for items to inflate/bind in between view system traversals on devices running API 21 or greater. Default value is true.

On platforms API level 21 and higher, the UI thread is idle between passing a frame to RenderThread and the starting up its next frame at the next VSync pulse. By prefetching out of window views in this time period, delays from inflation and view binding are much less likely to cause jank and stuttering during scrolls and flings.

While prefetch is enabled, it will have the side effect of expanding the effective size of the View cache to hold prefetched views.

Parameters
enabled Boolean: True if items should be prefetched in between traversals.

getPaddingLeft

open fun getPaddingLeft(): Int

Return the left padding of the parent RecyclerView

Return
Int: Padding in pixels

getPaddingTop

open fun getPaddingTop(): Int

Return the top padding of the parent RecyclerView

Return
Int: Padding in pixels

findContainingItemView

open fun findContainingItemView(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.

getRightDecorationWidth

open fun getRightDecorationWidth(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.

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.

getDecoratedMeasuredHeight

open fun getDecoratedMeasuredHeight(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

startSmoothScroll

open fun startSmoothScroll(smoothScroller: RecyclerView.SmoothScroller!): Unit

Starts a smooth scroll using the provided SmoothScroller.

Calling this method will cancel any previous smooth scroll request.

Parameters
smoothScroller RecyclerView.SmoothScroller!: Instance which defines how smooth scroll should be animated

getPaddingBottom

open fun getPaddingBottom(): Int

Return the bottom padding of the parent RecyclerView

Return
Int: Padding in pixels

getMinimumHeight

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

getDecoratedRight

open fun getDecoratedRight(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

onInterceptFocusSearch

open fun onInterceptFocusSearch(focused: View, direction: Int): View?

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 View: The currently focused view
direction View: One of View#FOCUS_UP, View#FOCUS_DOWN, View#FOCUS_LEFT, View#FOCUS_RIGHT, View#FOCUS_BACKWARD, View#FOCUS_FORWARD
Return
View?: A descendant view to focus or null to fall back to default behavior. The default implementation returns null.

getSelectionModeForAccessibility

open fun getSelectionModeForAccessibility(recycler: RecyclerView.Recycler, 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.Recycler: The current state of RecyclerView
Return
Int: Selection mode for accessibility. Default implementation returns AccessibilityNodeInfoCompat.CollectionInfoCompat#SELECTION_MODE_NONE.

requestChildRectangleOnScreen

open fun requestChildRectangleOnScreen(parent: RecyclerView, child: View, rect: Rect, immediate: Boolean): Boolean

Called when a child of the RecyclerView wants a particular rectangle to be positioned onto the screen. See ViewParent#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 RecyclerView: The direct child making the request.
rect RecyclerView: The rectangle in the child's coordinates the child wishes to be on the screen.
immediate RecyclerView: True to forbid animated or delayed scrolling, false otherwise
Return
Boolean: Whether the group scrolled to handle the operation

requestChildRectangleOnScreen

open fun requestChildRectangleOnScreen(parent: RecyclerView, child: View, rect: Rect, immediate: Boolean, focusedChildVisible: Boolean): Boolean

Requests that the given child of the RecyclerView be positioned onto the screen. This method can be called for both unfocusable and focusable child views. For unfocusable child views, focusedChildVisible is typically true in which case, layout manager makes the child view visible only if the currently focused child stays in-bounds of RV.

Parameters
parent RecyclerView: The parent RecyclerView.
child RecyclerView: The direct child making the request.
rect RecyclerView: The rectangle in the child's coordinates the child wishes to be on the screen.
immediate RecyclerView: True to forbid animated or delayed scrolling, false otherwise
focusedChildVisible RecyclerView: Whether the currently focused view must stay visible.
Return
Boolean: Whether the group scrolled to handle the operation

stopIgnoringView

open fun stopIgnoringView(view: View): Unit

View can be scrapped and recycled again.

Note that calling this method removes all information in the view holder.

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

Parameters
view View: View to ignore.

onDetachedFromWindow

open fun onDetachedFromWindow(view: RecyclerView!): Unit

onDetachedFromWindow

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

setMeasurementCacheEnabled

open fun setMeasurementCacheEnabled(measurementCacheEnabled: Boolean): Unit

Sets whether RecyclerView should use its own measurement cache for the children. This is a more aggressive cache than the framework uses.

Parameters
measurementCacheEnabled Boolean: True to enable the measurement cache, false otherwise.

onInitializeAccessibilityNodeInfo

open fun onInitializeAccessibilityNodeInfo(recycler: RecyclerView.Recycler, state: RecyclerView.State, info: AccessibilityNodeInfoCompat): Unit

Called by the AccessibilityDelegate when the information about the current layout should be populated.

Default implementation adds a .

You should override #getRowCountForAccessibility(RecyclerView.Recycler, RecyclerView.State), #getColumnCountForAccessibility(RecyclerView.Recycler, RecyclerView.State), #isLayoutHierarchical(RecyclerView.Recycler, RecyclerView.State) and #getSelectionModeForAccessibility(RecyclerView.Recycler, RecyclerView.State) for more accurate accessibility information.

Parameters
recycler RecyclerView.Recycler: The Recycler that can be used to convert view positions into adapter positions
state RecyclerView.Recycler: The current state of RecyclerView
info RecyclerView.Recycler: The info that should be filled by the LayoutManager

getColumnCountForAccessibility

open fun getColumnCountForAccessibility(recycler: RecyclerView.Recycler, 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.Recycler: The current state of RecyclerView
Return
Int: The number of rows in LayoutManager for accessibility.

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

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

onItemsChanged

open fun onItemsChanged(recyclerView: RecyclerView): Unit

Called in response to a call to Adapter#notifyDataSetChanged() or RecyclerView#swapAdapter(Adapter, boolean) ()} and signals that the the entire data set has changed.

Parameters
recyclerView RecyclerView:

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 View!: Index of the view.

removeDetachedView

open fun removeDetachedView(child: View): Unit

Finish removing a view that was previously temporarily detached.

Parameters
child View: Detached child to remove

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.

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

onItemsUpdated

open fun onItemsUpdated(recyclerView: RecyclerView, positionStart: Int, itemCount: Int): Unit

Called when items have been changed in the adapter. To receive payload, override #onItemsUpdated(RecyclerView, int, int, Object) instead, then this callback will not be invoked.

Parameters
recyclerView RecyclerView:
positionStart RecyclerView:
itemCount RecyclerView:

onItemsUpdated

open fun onItemsUpdated(recyclerView: RecyclerView, positionStart: Int, itemCount: Int, payload: Any?): Unit

Called when items have been changed in the adapter and with optional payload. Default implementation calls #onItemsUpdated(RecyclerView, int, int).

Parameters
recyclerView RecyclerView:
positionStart RecyclerView:
itemCount RecyclerView:
payload RecyclerView:

onRestoreInstanceState

open fun onRestoreInstanceState(state: Parcelable!): Unit

getDecoratedBottom

open fun getDecoratedBottom(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

offsetChildrenVertical

open fun offsetChildrenVertical(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

getTopDecorationHeight

open fun getTopDecorationHeight(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.

setMeasuredDimension

open fun setMeasuredDimension(childrenBounds: Rect!, wSpec: Int, hSpec: Int): Unit

Sets the measured dimensions from the given bounding box of the children and the measurement specs that were passed into RecyclerView#onMeasure(int, int). It is only called if a LayoutManager returns true from #isAutoMeasureEnabled() and it is called after the RecyclerView calls LayoutManager#onLayoutChildren(Recycler, State) in the execution of RecyclerView#onMeasure(int, int).

This method must call #setMeasuredDimension(int, int).

The default implementation adds the RecyclerView's padding to the given bounding box then caps the value to be within the given measurement specs.

Parameters
childrenBounds Rect!: The bounding box of all children
wSpec Rect!: The widthMeasureSpec that was passed into the RecyclerView.
hSpec Rect!: The heightMeasureSpec that was passed into the RecyclerView.

setMeasuredDimension

open fun setMeasuredDimension(widthSize: Int, heightSize: Int): Unit

Set the measured dimensions of the host RecyclerView.

Parameters
widthSize Int: Measured width
heightSize Int: Measured height

getItemViewType

open fun getItemViewType(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.

removeAndRecycleAllViews

open fun removeAndRecycleAllViews(recycler: RecyclerView.Recycler): Unit

Removes all views and recycles them using the given recycler.

If you want to clean cached views as well, you should call Recycler#clear() too.

If a View is marked as "ignored", it is not removed nor recycled.

Parameters
recycler RecyclerView.Recycler: Recycler to use to recycle children

onLayoutChildren

open fun onLayoutChildren(recycler: RecyclerView.Recycler!, state: RecyclerView.State!): Unit

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

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

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

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

Parameters
recycler RecyclerView.Recycler!: Recycler to use for fetching potentially cached views for a position
state RecyclerView.Recycler!: Transient state of RecyclerView

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

getWidth

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

isLayoutHierarchical

open fun isLayoutHierarchical(recycler: RecyclerView.Recycler, 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.Recycler: The current state of RecyclerView
Return
Boolean: True if layout is hierarchical.

getBottomDecorationHeight

open fun getBottomDecorationHeight(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.

onScrollStateChanged

open fun onScrollStateChanged(state: Int): Unit

RecyclerView calls this method to notify LayoutManager that scroll state has changed.

Parameters
state Int: The new scroll state for RecyclerView

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

getChildMeasureSpec

open static fun getChildMeasureSpec(parentSize: 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
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 Int: 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 Int: true if the parent RecyclerView can scroll in this dimension
Return
Int: a MeasureSpec value for the child view

getProperties

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

Parse the xml attributes to get the most common properties used by layout managers.

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