LayoutManager

<init>

LayoutManager()

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

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.

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.

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).

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).

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.

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.

attachView

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

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

attachView

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

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

attachView

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

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

calculateItemDecorationsForChild

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

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

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

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

canScrollHorizontally

open fun canScrollHorizontally(): Boolean

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

canScrollVertically

open fun canScrollVertically(): Boolean

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

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.

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.

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.

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.

computeHorizontalScrollExtent

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

Override this method if you want to support scroll bars.

Read RecyclerView#computeHorizontalScrollExtent() for details.

Default implementation returns 0.

computeHorizontalScrollOffset

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

Override this method if you want to support scroll bars.

Read RecyclerView#computeHorizontalScrollOffset() for details.

Default implementation returns 0.

computeHorizontalScrollRange

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

Override this method if you want to support scroll bars.

Read RecyclerView#computeHorizontalScrollRange() for details.

Default implementation returns 0.

computeVerticalScrollExtent

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

Override this method if you want to support scroll bars.

Read RecyclerView#computeVerticalScrollExtent() for details.

Default implementation returns 0.

computeVerticalScrollOffset

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

Override this method if you want to support scroll bars.

Read RecyclerView#computeVerticalScrollOffset() for details.

Default implementation returns 0.

computeVerticalScrollRange

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

Override this method if you want to support scroll bars.

Read RecyclerView#computeVerticalScrollRange() for details.

Default implementation returns 0.

detachAndScrapAttachedViews

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

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

detachAndScrapView

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

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

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

detachAndScrapViewAt

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

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

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

detachView

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

Temporarily detach a child view.

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

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

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.

endAnimation

open fun endAnimation(view: View!): Unit

Ends all animations on the view created by the ItemAnimator.

findContainingItemView

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

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

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

findViewByPosition

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

Finds the view which represents the given adapter position.

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

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

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).

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).

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).

getBaseline

open fun getBaseline(): Int

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

getBottomDecorationHeight

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

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

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

getChildAt

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

Return the child view at the given index

getChildCount

open fun getChildCount(): Int

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

getChildMeasureSpec

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

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

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

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.

getClipToPadding

open fun getClipToPadding(): Boolean

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

getColumnCountForAccessibility

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

Returns the number of columns for accessibility.

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

getDecoratedBottom

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

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

getDecoratedBoundsWithMargins

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

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

getDecoratedLeft

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

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

getDecoratedMeasuredHeight

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

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

getDecoratedMeasuredWidth

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

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

getDecoratedRight

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

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

getDecoratedTop

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

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

getFocusedChild

@Nullable open fun getFocusedChild(): View?

Returns the item View which has or contains focus.

getHeight

@Px open fun getHeight(): Int

Returns the height that is currently relevant to the LayoutManager.

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

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.

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().

getItemViewType

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

Returns the View type defined by the adapter.

getLayoutDirection

open fun getLayoutDirection(): Int

Returns the resolved layout direction for this RecyclerView.

getLeftDecorationWidth

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

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

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

getMinimumHeight

@Px open fun getMinimumHeight(): Int

getMinimumWidth

@Px open fun getMinimumWidth(): Int

getPaddingBottom

@Px open fun getPaddingBottom(): Int

Return the bottom padding of the parent RecyclerView

getPaddingEnd

@Px open fun getPaddingEnd(): Int

Return the end padding of the parent RecyclerView

getPaddingLeft

@Px open fun getPaddingLeft(): Int

Return the left padding of the parent RecyclerView

getPaddingRight

@Px open fun getPaddingRight(): Int

Return the right padding of the parent RecyclerView

getPaddingStart

@Px open fun getPaddingStart(): Int

Return the start padding of the parent RecyclerView

getPaddingTop

@Px open fun getPaddingTop(): Int

Return the top padding of the parent RecyclerView

getPosition

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

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

getProperties

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

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

getRightDecorationWidth

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

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

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

getRowCountForAccessibility

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

Returns the number of rows for accessibility.

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

getSelectionModeForAccessibility

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

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

Default implementation returns AccessibilityNodeInfoCompat.CollectionInfoCompat#SELECTION_MODE_NONE.

getTopDecorationHeight

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

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

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

getTransformedBoundingBox

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

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

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

getWidth

@Px open fun getWidth(): Int

Returns the width that is currently relevant to the LayoutManager.

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

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.

hasFocus

open fun hasFocus(): Boolean

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

ignoreView

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

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

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

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

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

isAttachedToWindow

open fun isAttachedToWindow(): Boolean

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

isAutoMeasureEnabled

open fun isAutoMeasureEnabled(): Boolean

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

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

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

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

More specifically:

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

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

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

isFocused

open fun isFocused(): Boolean

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

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.

isLayoutHierarchical

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

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

Default implementation returns false.

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).

isSmoothScrolling

open fun isSmoothScrolling(): Boolean

isViewPartiallyVisible

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

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

layoutDecorated

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

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

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

• layoutDecoratedWithMargins(View, int, int, int, int)
• getDecoratedBoundsWithMargins(View, Rect)
• measureChild(View, int, int)
• measureChildWithMargins(View, int, int)
• getDecoratedLeft(View)
• getDecoratedTop(View)
• getDecoratedRight(View)
• getDecoratedBottom(View)
• getDecoratedMeasuredWidth(View)
• getDecoratedMeasuredHeight(View)

layoutDecoratedWithMargins

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

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

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

• layoutDecorated(View, int, int, int, int)
• measureChild(View, int, int)
• measureChildWithMargins(View, int, int)
• getDecoratedLeft(View)
• getDecoratedTop(View)
• getDecoratedRight(View)
• getDecoratedBottom(View)
• getDecoratedMeasuredWidth(View)
• getDecoratedMeasuredHeight(View)

measureChild

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

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

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

measureChildWithMargins

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

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

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

moveView

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

Moves a View from one position to another.

offsetChildrenHorizontal

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

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

offsetChildrenVertical

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

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

onAdapterChanged

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

Called if the RecyclerView this LayoutManager is bound to has a different adapter set via RecyclerView#setAdapter(Adapter) or RecyclerView#swapAdapter(Adapter, boolean). The LayoutManager may use this opportunity to clear caches and configure state such that it can relayout appropriately with the new data and potentially new view types.

The default implementation removes all currently attached views.

onAddFocusables

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

Called to populate focusable views within the RecyclerView.

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

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

onAttachedToWindow

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

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

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

Subclass implementations should always call through to the superclass implementation.

onDetachedFromWindow

open fun onDetachedFromWindow(view: RecyclerView!): Unit

Deprecated: override onDetachedFromWindow(RecyclerView, Recycler)

onDetachedFromWindow

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

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

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

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

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

Subclass implementations should always call through to the superclass implementation.

onFocusSearchFailed

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

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

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

onInitializeAccessibilityEvent