RecyclerView.LayoutManager

RecyclerView.LayoutManager

RecyclerView.LayoutManager ()

addDisappearingView

void addDisappearingView (View child, 
                int index)

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

void addDisappearingView (View child)

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

void addView (View child, 
                int index)

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

addView

void addView (View child)

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

assertInLayoutOrScroll

void assertInLayoutOrScroll (String message)

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

assertNotInLayoutOrScroll

void assertNotInLayoutOrScroll (String message)

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

attachView

void attachView (View child)

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

attachView

void attachView (View child, 
                int index)

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

attachView

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

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

calculateItemDecorationsForChild

void calculateItemDecorationsForChild (View child, 
                Rect outRect)

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(int, int), you can use this method to get decorations.

canScrollHorizontally

boolean canScrollHorizontally ()

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

canScrollVertically

boolean canScrollVertically ()

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

checkLayoutParams

boolean checkLayoutParams (RecyclerView.LayoutParams lp)

Determines the validity of the supplied LayoutParams object.

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

chooseSize

int chooseSize (int spec, 
                int desired, 
                int min)

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

collectAdjacentPrefetchPositions

void collectAdjacentPrefetchPositions (int dx, 
                int dy, 
                RecyclerView.State state, 
                RecyclerView.LayoutManager.LayoutPrefetchRegistry layoutPrefetchRegistry)

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(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

void collectInitialPrefetchPositions (int adapterItemCount, 
                RecyclerView.LayoutManager.LayoutPrefetchRegistry layoutPrefetchRegistry)

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(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

int computeHorizontalScrollExtent (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read computeHorizontalScrollExtent() for details.

Default implementation returns 0.

computeHorizontalScrollOffset

int computeHorizontalScrollOffset (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read computeHorizontalScrollOffset() for details.

Default implementation returns 0.

computeHorizontalScrollRange

int computeHorizontalScrollRange (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read computeHorizontalScrollRange() for details.

Default implementation returns 0.

computeVerticalScrollExtent

int computeVerticalScrollExtent (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read computeVerticalScrollExtent() for details.

Default implementation returns 0.

computeVerticalScrollOffset

int computeVerticalScrollOffset (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read computeVerticalScrollOffset() for details.

Default implementation returns 0.

computeVerticalScrollRange

int computeVerticalScrollRange (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read computeVerticalScrollRange() for details.

Default implementation returns 0.

detachAndScrapAttachedViews

void detachAndScrapAttachedViews (RecyclerView.Recycler recycler)

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

detachAndScrapView

void detachAndScrapView (View child, 
                RecyclerView.Recycler recycler)

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

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

detachAndScrapViewAt

void detachAndScrapViewAt (int index, 
                RecyclerView.Recycler recycler)

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

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

detachView

void detachView (View child)

Temporarily detach a child view.

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

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

detachViewAt

void detachViewAt (int index)

Temporarily detach a child view.

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

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

endAnimation

void endAnimation (View view)

Ends all animations on the view created by the RecyclerView.ItemAnimator.

findContainingItemView

View findContainingItemView (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

View findViewByPosition (int position)

Finds the view which represents the given adapter position.

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

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

generateDefaultLayoutParams

RecyclerView.LayoutParams generateDefaultLayoutParams ()

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

LayoutManagers will often want to use a custom LayoutParams type to store extra information specific to the layout. Client code should subclass RecyclerView.LayoutParams for this purpose.

Important: if you use your own custom LayoutParams type you must also override checkLayoutParams(LayoutParams), generateLayoutParams(android.view.ViewGroup.LayoutParams) and generateLayoutParams(android.content.Context, android.util.AttributeSet).

generateLayoutParams

RecyclerView.LayoutParams generateLayoutParams (Context c, 
                AttributeSet attrs)

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

Important: if you use your own custom LayoutParams type you must also override checkLayoutParams(LayoutParams), generateLayoutParams(android.view.ViewGroup.LayoutParams) and generateLayoutParams(android.content.Context, android.util.AttributeSet).

generateLayoutParams

RecyclerView.LayoutParams generateLayoutParams (ViewGroup.LayoutParams lp)

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

Important: if you use your own custom LayoutParams type you must also override checkLayoutParams(LayoutParams), generateLayoutParams(android.view.ViewGroup.LayoutParams) and generateLayoutParams(android.content.Context, android.util.AttributeSet).

getBaseline

int getBaseline ()

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

getBottomDecorationHeight

int getBottomDecorationHeight (View child)

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

View getChildAt (int index)

Return the child view at the given index

getChildCount

int getChildCount ()

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

getChildMeasureSpec

int getChildMeasureSpec (int parentSize, 
                int parentMode, 
                int padding, 
                int childDimension, 
                boolean canScroll)

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

getChildMeasureSpec

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

This method was deprecated in API level 24.1.0.
use getChildMeasureSpec(int, int, int, int, boolean)

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

getClipToPadding

boolean getClipToPadding ()

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

getColumnCountForAccessibility

int getColumnCountForAccessibility (RecyclerView.Recycler recycler, 
                RecyclerView.State state)

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

int getDecoratedBottom (View child)

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

getDecoratedBoundsWithMargins

void getDecoratedBoundsWithMargins (View view, 
                Rect outBounds)

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

getDecoratedLeft

int getDecoratedLeft (View child)

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

getDecoratedMeasuredHeight

int getDecoratedMeasuredHeight (View child)

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

getDecoratedMeasuredWidth

int getDecoratedMeasuredWidth (View child)

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

getDecoratedRight

int getDecoratedRight (View child)

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

getDecoratedTop

int getDecoratedTop (View child)

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

getFocusedChild

View getFocusedChild ()

Returns the item View which has or contains focus.

getHeight

int getHeight ()

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 View.MeasureSpec height if the RecyclerView.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

int getHeightMode ()

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 EXACTLY even if it was measured with a different spec mode.

getItemCount

int getItemCount ()

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 RecyclerView.State is available, you should use State#getItemCount() instead. For more details, check the documentation for State#getItemCount().

getItemViewType

int getItemViewType (View view)

Returns the View type defined by the adapter.

getLayoutDirection

int getLayoutDirection ()

Returns the resolved layout direction for this RecyclerView.

getLeftDecorationWidth

int getLeftDecorationWidth (View child)

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

int getMinimumHeight ()

getMinimumWidth

int getMinimumWidth ()

getPaddingBottom

int getPaddingBottom ()

Return the bottom padding of the parent RecyclerView

getPaddingEnd

int getPaddingEnd ()

Return the end padding of the parent RecyclerView

getPaddingLeft

int getPaddingLeft ()

Return the left padding of the parent RecyclerView

getPaddingRight

int getPaddingRight ()

Return the right padding of the parent RecyclerView

getPaddingStart

int getPaddingStart ()

Return the start padding of the parent RecyclerView

getPaddingTop

int getPaddingTop ()

Return the top padding of the parent RecyclerView

getPosition

int getPosition (View view)

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

RecyclerView.LayoutManager.Properties getProperties (Context context, 
                AttributeSet attrs, 
                int defStyleAttr, 
                int defStyleRes)

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

Related XML Attributes:

• RecyclerView_android_orientation
• RecyclerView_spanCount
• RecyclerView_reverseLayout
• RecyclerView_stackFromEnd

getRightDecorationWidth

int getRightDecorationWidth (View child)

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

int getRowCountForAccessibility (RecyclerView.Recycler recycler, 
                RecyclerView.State state)

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

int getSelectionModeForAccessibility (RecyclerView.Recycler recycler, 
                RecyclerView.State state)

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

Default implementation returns SELECTION_MODE_NONE.

getTopDecorationHeight

int getTopDecorationHeight (View child)

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

void getTransformedBoundingBox (View child, 
                boolean includeDecorInsets, 
                Rect out)

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

int getWidth ()

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 View.MeasureSpec width if the RecyclerView.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

int getWidthMode ()

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 EXACTLY even if it was measured with a different spec mode.

hasFocus

boolean hasFocus ()

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

ignoreView

void ignoreView (View view)

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

boolean isAttachedToWindow ()

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

isAutoMeasureEnabled

boolean isAutoMeasureEnabled ()

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(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, 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 onLayoutChildren(Recycler, State) during a call to 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 onMeasure(int, int) 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(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 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 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(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 onMeasure(int, int) will run onLayoutChildren(Recycler, State) 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(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

boolean isFocused ()

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

isItemPrefetchEnabled

boolean isItemPrefetchEnabled ()

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

isLayoutHierarchical

boolean isLayoutHierarchical (RecyclerView.Recycler recycler, 
                RecyclerView.State state)

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

Default implementation returns false.

isMeasurementCacheEnabled

boolean isMeasurementCacheEnabled ()

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

boolean isSmoothScrolling ()

isViewPartiallyVisible

boolean isViewPartiallyVisible (View child, 
                boolean completelyVisible, 
                boolean acceptEndPointInclusion)

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

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

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

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

• 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

void layoutDecoratedWithMargins (View child, 
                int left, 
                int top, 
                int right, 
                int bottom)

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

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

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

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

measureChildWithMargins

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

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

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

moveView

void moveView (int fromIndex, 
                int toIndex)

Moves a View from one position to another.

offsetChildrenHorizontal

void offsetChildrenHorizontal (int dx)

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

offsetChildrenVertical

void offsetChildrenVertical (int dy)

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

onAdapterChanged

void onAdapterChanged (Adapter oldAdapter, 
                Adapter newAdapter)

Called if the RecyclerView this LayoutManager is bound to has a different adapter set via setAdapter(Adapter) or 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

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

Called to populate focusable views within the RecyclerView.

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

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

onAttachedToWindow

void onAttachedToWindow (RecyclerView view)

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

void onDetachedFromWindow (RecyclerView view, 
                RecyclerView.Recycler recycler)

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 requestLayout() to ensure that it is re-laid out when RecyclerView is re-attached.

Subclass implementations should always call through to the superclass implementation.

onDetachedFromWindow

void onDetachedFromWindow (RecyclerView view)

This method was deprecated in API level 22.1.0.
override onDetachedFromWindow(RecyclerView, Recycler)

onFocusSearchFailed

View onFocusSearchFailed (View focused, 
                int direction, 
                RecyclerView.Recycler recycler, 
                RecyclerView.State state)

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

This is the LayoutManager's opportunity to populate views in the given direction to fulfill the request if it can. The LayoutManager should attach and return the view to be focused, 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

void onInitializeAccessibilityEvent (AccessibilityEvent event)

onInitializeAccessibilityEvent

void onInitializeAccessibilityEvent (RecyclerView.Recycler recycler, 
                RecyclerView.State state, 
                AccessibilityEvent event)

Called by the accessibility delegate to initialize an accessibility event.

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

onInitializeAccessibilityNodeInfo

void onInitializeAccessibilityNodeInfo (RecyclerView.Recycler recycler, 
                RecyclerView.State state, 
                AccessibilityNodeInfoCompat info)

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

Default implementation adds a AccessibilityNodeInfoCompat.CollectionInfoCompat.

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.

onInitializeAccessibilityNodeInfoForItem

void onInitializeAccessibilityNodeInfoForItem (RecyclerView.Recycler recycler, 
                RecyclerView.State state, 
                View host, 
                AccessibilityNodeInfoCompat info)

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

Default implementation adds basic positioning information about the item.

onInterceptFocusSearch

View onInterceptFocusSearch (View focused, 
                int direction)

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

onItemsAdded

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

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

onItemsChanged

void onItemsChanged (RecyclerView recyclerView)

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

onItemsMoved

void onItemsMoved (RecyclerView recyclerView, 
                int from, 
                int to, 
                int itemCount)

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(int, int) is called.

onItemsRemoved

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

Called when items have been removed from the adapter.

onItemsUpdated

void onItemsUpdated (RecyclerView recyclerView, 
                int positionStart, 
                int itemCount)

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.

onItemsUpdated

void onItemsUpdated (RecyclerView recyclerView, 
                int positionStart, 
                int itemCount, 
                Object payload)

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

onLayoutChildren

void onLayoutChildren (RecyclerView.Recycler recycler, 
                RecyclerView.State state)

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

onLayoutCompleted

void onLayoutCompleted (RecyclerView.State state)

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 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.

onMeasure

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

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.

onRequestChildFocus

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

This method was deprecated in API level 22.1.0.
Use onRequestChildFocus(RecyclerView, State, View, View)

onRequestChildFocus

boolean onRequestChildFocus (RecyclerView parent, 
                RecyclerView.State state, 
                View child, 
                View focused)

Called when a descendant view of the RecyclerView requests focus.

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

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

onRestoreInstanceState

void onRestoreInstanceState (Parcelable state)

onSaveInstanceState

Parcelable onSaveInstanceState ()

Called when the LayoutManager should save its state. This is a good time to save your scroll position, configuration and anything else that may be required to restore the same layout state if the LayoutManager is recreated.

RecyclerView does NOT verify if the LayoutManager has changed between state save and restore. This will let you share information between your LayoutManagers but it is also your responsibility to make sure they use the same parcelable class.

onScrollStateChanged

void onScrollStateChanged (int state)

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

performAccessibilityAction

boolean performAccessibilityAction (RecyclerView.Recycler recycler, 
                RecyclerView.State state, 
                int action, 
                Bundle args)

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

performAccessibilityActionForItem

boolean performAccessibilityActionForItem (RecyclerView.Recycler recycler, 
                RecyclerView.State state, 
                View view, 
                int action, 
                Bundle args)

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

Default implementation does not do anything.

postOnAnimation

void postOnAnimation (Runnable action)

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.

removeAllViews

void removeAllViews ()

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

removeAndRecycleAllViews

void removeAndRecycleAllViews (RecyclerView.Recycler recycler)

Removes all views and recycles them using the given recycler.

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

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

removeAndRecycleView

void removeAndRecycleView (View child, 
                RecyclerView.Recycler recycler)

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

removeAndRecycleViewAt

void removeAndRecycleViewAt (int index, 
                RecyclerView.Recycler recycler)

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

removeCallbacks

boolean removeCallbacks (Runnable action)

Removes the specified Runnable from the message queue.

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

removeDetachedView

void removeDetachedView (View child)

Finish removing a view that was previously temporarily detached.

removeView

void removeView (View child)

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

removeViewAt

void removeViewAt (int index)

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

requestChildRectangleOnScreen

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

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.

requestChildRectangleOnScreen

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

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

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

requestLayout

void requestLayout ()

Calls RecyclerView#requestLayout on the underlying RecyclerView

requestSimpleAnimationsInNextLayout

void requestSimpleAnimationsInNextLayout ()

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 RecyclerView.ItemAnimator set, RecyclerView will not run any animations but will still clear this flag after the layout is complete.

scrollHorizontallyBy

int scrollHorizontallyBy (int dx, 
                RecyclerView.Recycler recycler, 
                RecyclerView.State state)

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

scrollToPosition

void scrollToPosition (int position)

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

scrollVerticallyBy

int scrollVerticallyBy (int dy, 
                RecyclerView.Recycler recycler, 
                RecyclerView.State state)

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

setAutoMeasureEnabled

void setAutoMeasureEnabled (boolean enabled)

This method was deprecated in API level 27.1.0.
Implementors of LayoutManager should define whether or not it uses AutoMeasure by overriding isAutoMeasureEnabled().

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 onMeasure(Recycler, State, int, int).

setItemPrefetchEnabled

void setItemPrefetchEnabled (boolean enabled)

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.

setMeasuredDimension

void setMeasuredDimension (int widthSize, 
                int heightSize)

Set the measured dimensions of the host RecyclerView.

setMeasuredDimension

void setMeasuredDimension (Rect childrenBounds, 
                int wSpec, 
                int hSpec)

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

setMeasurementCacheEnabled

void setMeasurementCacheEnabled (boolean measurementCacheEnabled)

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

smoothScrollToPosition

void smoothScrollToPosition (RecyclerView recyclerView, 
                RecyclerView.State state, 
                int position)

Smooth scroll to the specified adapter position.

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

startSmoothScroll

void startSmoothScroll (RecyclerView.SmoothScroller smoothScroller)

Starts a smooth scroll using the provided SmoothScroller.

Calling this method will cancel any previous smooth scroll request.

stopIgnoringView

void stopIgnoringView (View view)

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.

supportsPredictiveItemAnimations

boolean supportsPredictiveItemAnimations ()

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.