RecyclerView.LayoutManager

fun addDisappearingView(child: View!): Unit

To be called only during onLayoutChildren 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 or won't be included in getChildCount method.

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

To be called only during onLayoutChildren 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 or won't be included in getChildCount method.

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 getViewForPosition.

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 getViewForPosition.

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.

fun assertNotInLayoutOrScroll(message: String!): Unit

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

fun attachView(child: View): Unit

Reattach a previously detached view. This method should not be used to reattach views that were previously detachAndScrapView scrapped}.

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 scrapped}.

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 scrapped}.

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 measure, you can use this method to get decorations.

fun canScrollHorizontally(): Boolean

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

fun canScrollVertically(): Boolean

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

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.

java-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.

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 addPosition 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.

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 addPosition 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.

fun computeHorizontalScrollExtent(state: RecyclerView.State): Int

Override this method if you want to support scroll bars.

Read computeHorizontalScrollExtent for details.

Default implementation returns 0.

fun computeHorizontalScrollOffset(state: RecyclerView.State): Int

Override this method if you want to support scroll bars.

Read computeHorizontalScrollOffset for details.

Default implementation returns 0.

fun computeHorizontalScrollRange(state: RecyclerView.State): Int

Override this method if you want to support scroll bars.

Read computeHorizontalScrollRange for details.

Default implementation returns 0.

fun computeVerticalScrollExtent(state: RecyclerView.State): Int

Override this method if you want to support scroll bars.

Read computeVerticalScrollExtent for details.

Default implementation returns 0.

fun computeVerticalScrollOffset(state: RecyclerView.State): Int

Override this method if you want to support scroll bars.

Read computeVerticalScrollOffset for details.

Default implementation returns 0.

fun computeVerticalScrollRange(state: RecyclerView.State): Int

Override this method if you want to support scroll bars.

Read computeVerticalScrollRange for details.

Default implementation returns 0.

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.

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.

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.

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 so that the detached view may be rebound and reused.

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

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 so that the detached view may be rebound and reused.

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

fun endAnimation(view: View!): Unit

Ends all animations on the view created by the ItemAnimator.

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).

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, it is also ignored by this method.

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, generateLayoutParams and generateLayoutParams.

fun generateLayoutParams(lp: ViewGroup.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, generateLayoutParams and generateLayoutParams.

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, generateLayoutParams and generateLayoutParams.

fun getBaseline(): Int

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

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 is called.

fun getChildAt(index: Int): View?

Return the child view at the given index

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.

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

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

java-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.

fun getClipToPadding(): Boolean

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

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.

fun getDecoratedBottom(child: View): Int

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

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

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

fun getDecoratedLeft(child: View): Int

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

fun getDecoratedMeasuredHeight(child: View): Int

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

fun getDecoratedMeasuredWidth(child: View): Int

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

fun getDecoratedRight(child: View): Int

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

fun getDecoratedTop(child: View): Int

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

fun getFocusedChild(): View?

Returns the item View which has or contains focus.

fun getHeight(): @Px 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.

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.

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

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().

fun getItemViewType(view: View): Int

Returns the View type defined by the adapter.

fun getLayoutDirection(): Int

Returns the resolved layout direction for this RecyclerView.

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 is called.

fun getPaddingBottom(): @Px Int

Return the bottom padding of the parent RecyclerView

fun getPaddingEnd(): @Px Int

Return the end padding of the parent RecyclerView

fun getPaddingLeft(): @Px Int

Return the left padding of the parent RecyclerView

fun getPaddingRight(): @Px Int

Return the right padding of the parent RecyclerView

fun getPaddingStart(): @Px Int

Return the start padding of the parent RecyclerView

fun getPaddingTop(): @Px Int

Return the top padding of the parent RecyclerView

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.

java-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. orientationspanCountreverseLayoutstackFromEnd

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 is called.

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.

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

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

Default implementation returns SELECTION_MODE_NONE.

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 is called.

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.

fun getWidth(): @Px 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.

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.

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

fun hasFocus(): Boolean

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

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 will ignore the child whereas removeAllViews or offsetChildrenHorizontal will not ignore the child.

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

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

fun isAttachedToWindow(): Boolean

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

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 onMeasure.

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

If this method is overridden to return true, onMeasure should not be overridden.

AutoMeasure is a RecyclerView mechanism that handles the measuring pass of layout in a simple and contract satisfying way, including the wrapping of children laid out by LayoutManager. Simply put, it handles wrapping children by calling onLayoutChildren during a call to onMeasure, 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 onMeasure is called, if the provided measure specs both have a mode of EXACTLY, RecyclerView will set its measured dimensions accordingly and return, allowing layout to continue as normal (Actually, RecyclerView will call onMeasure 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 with 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 with isMeasuring set to true and 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 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 onMeasure will run onLayoutChildren with isMeasuring set to true and 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 call as if it is the last one.
5. When measure is complete and RecyclerView's onLayout 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 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.

fun isFocused(): Boolean

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

fun isItemPrefetchEnabled(): Boolean

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

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.

fun isLayoutReversed(): Boolean

Query if the layout is in reverse order. This will affect, for example, keyboard navigation via page up/page down. The default implementation returns false.

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.

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.

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:

• layoutDecoratedWithMargins
• getDecoratedBoundsWithMargins
• measureChild
• measureChildWithMargins
• getDecoratedLeft
• getDecoratedTop
• getDecoratedRight
• getDecoratedBottom
• getDecoratedMeasuredWidth
• getDecoratedMeasuredHeight

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:

• layoutDecorated
• measureChild
• measureChildWithMargins
• getDecoratedLeft
• getDecoratedTop
• getDecoratedRight
• getDecoratedBottom
• getDecoratedMeasuredWidth
• getDecoratedMeasuredHeight

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.

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.

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

Moves a View from one position to another.

fun offsetChildrenHorizontal(dx: @Px Int): Unit

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

fun offsetChildrenVertical(dy: @Px Int): Unit

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

fun onAdapterChanged(
    oldAdapter: RecyclerView.Adapter?,
    newAdapter: RecyclerView.Adapter?
): Unit

Called if the RecyclerView this LayoutManager is bound to has a different adapter set via setAdapter or swapAdapter. 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.

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 addFocusables should be suppressed.

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

@CallSuper
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 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.

@CallSuper
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 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 requestLayout to ensure that it is re-laid out when RecyclerView is re-attached.

Subclass implementations should always call through to the superclass implementation.

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.

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.

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, getColumnCountForAccessibility, isLayoutHierarchical and getSelectionModeForAccessibility for more accurate accessibility information.

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.

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 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.

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.)

fun onItemsChanged(recyclerView: RecyclerView): Unit

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

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 notifyItemMoved is called.

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

Called when items have been removed from the adapter.

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

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

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.

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, 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. Supporting predictive animations means that onLayoutChildren 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.

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

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

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

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

Measure the attached RecyclerView. Implementations must call setMeasuredDimension 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.

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.

fun onRestoreInstanceState(state: Parcelable!): Unit

Called when the RecyclerView is ready to restore the state based on a previous RecyclerView. Notice that this might happen after an actual layout, based on how Adapter prefers to restore State. See getStateRestorationPolicy for more information.

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.

fun onScrollStateChanged(state: Int): Unit

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