Package 

Class RecyclerView.LayoutManager

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public abstract class RecyclerView.LayoutManager

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

    If the LayoutManager specifies a default constructor or one with the signature(Context, AttributeSet, {@code int}, {@code int}), RecyclerView willinstantiate and set the LayoutManager when being inflated. Most used properties canbe then obtained from getProperties. In casea LayoutManager specifies both constructors, the non-default constructor will takeprecedence.

    • Method Detail

      • setMeasuredDimension

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

        Sets the measured dimensions from the given bounding box of the children and themeasurement specs that were passed into onMeasure. It isonly called if a LayoutManager returns true from isAutoMeasureEnabled and it is called after the RecyclerView calls onLayoutChildren in the execution of onMeasure.

        This method must call setMeasuredDimension.

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

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

      • requestLayout

         void requestLayout()

        Calls {@code RecyclerView#requestLayout} on the underlying RecyclerView

      • chooseSize

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

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

        Parameters:
        spec - The measureSpec
        desired - The preferred measurement
        min - The minimum value

      • setAutoMeasureEnabled

        @Deprecated() void setAutoMeasureEnabled(boolean enabled)

        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.

        Parameters:
        enabled - True if layout measurement should be done by theRecyclerView, false if it should be done by thisLayoutManager.

      • 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.

        This method returns false by default (it actually returns the value passed to thedeprecated setAutoMeasureEnabled) and should be overridden to returntrue 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 asimple and contract satisfying way, including the wrapping of children laid out byLayoutManager. Simply put, it handles wrapping children by calling onLayoutChildren during a call to onMeasure, and then calculating desired dimensions basedon children's dimensions and positions. It does this while supporting all existinganimation capabilities of the RecyclerView.

        More specifically:

        • When onMeasure is called, if the provided measurespecs both have a mode of EXACTLY, RecyclerView will set itsmeasured dimensions accordingly and return, allowing layout to continue as normal(Actually, RecyclerView will call onMeasure for backwards compatibilityreasons but it should not be overridden if AutoMeasure is being used).
        • If one of the layout specs is not {@code EXACT}, the RecyclerView will start thelayout process. It will first process all pending Adapter updates andthen decide whether to run a predictive layout. If it decides to do so, it will firstcall onLayoutChildren with isPreLayout set to {@code true}. At this stage, getWidth and getHeight will stillreturn 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 {@code true} and isPreLayout set to {@code false}. The LayoutManager canaccess the measurement specs via getHeight, getHeightMode, getWidth and getWidthMode.

        • After the layout calculation, RecyclerView sets the measured width & height bycalculating the bounding box for the children (+ RecyclerView's padding). TheLayoutManagers can override setMeasuredDimension to choosedifferent values. For instance, GridLayoutManager overrides this value to handle the casewhere if it is vertical and has 3 columns but only 2 items, it should still measure itswidth to fit 3 items, not 2.
        • Any following calls to onMeasure will run onLayoutChildren with isMeasuring set to {@code true} and isPreLayout set to {@code false}. RecyclerView willtake care of which views are actually added / removed / moved / changed for animations sothat the LayoutManager should not worry about them and handle each onLayoutChildren call as if it is the last one.
        • When measure is complete and RecyclerView's onLayout method is called, RecyclerView checkswhether it already did layout calculations during the measure pass and if so, it re-usesthat information. It may still decide to call onLayoutChildren if the last measure spec was different from the final dimensions or adapter contentshave changed between the measure call and the layout call.
        • Finally, animations are calculated and run as usual.

      • supportsPredictiveItemAnimations

         boolean supportsPredictiveItemAnimations()

        Returns whether this LayoutManager supports "predictive item animations".

        "Predictive item animations" are automatically created animations that showwhere 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 thismethod to return true (the default implementation returns false) and must obey certainbehavioral contracts outlined in onLayoutChildren.

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

      • setItemPrefetchEnabled

         final void setItemPrefetchEnabled(boolean enabled)

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

        If enabled, the LayoutManager will be queried for items to inflate/bind in betweenview 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 frameto RenderThread and the starting up its next frame at the next VSync pulse. Byprefetching out of window views in this time period, delays from inflation and viewbinding 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 effectivesize of the View cache to hold prefetched views.

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

      • isItemPrefetchEnabled

         final boolean isItemPrefetchEnabled()

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

      • 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 gatherwhich positions the LayoutManager will soon need, given upcoming movement in subsequenttraversals.

        The LayoutManager should call addPosition foreach item to be prepared, and these positions will have their ViewHolders created andbound, if there is sufficient time available, in advance of being needed by ascroll or layout.

        Parameters:
        dx - X movement component.
        dy - Y movement component.
        state - State of RecyclerView
        layoutPrefetchRegistry - PrefetchRegistry to add prefetch entries into.

      • collectInitialPrefetchPositions

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

        Gather all positions from the LayoutManager to be prefetched in preperation for itsRecyclerView 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 containingLayoutManager, this method is called in between draw traversals to gatherwhich positions this LayoutManager will first need, once it appears on the screen.

        For example, if this LayoutManager represents a horizontally scrolling list within avertically scrolling LayoutManager, this method would be called when the horizontal listis about to come onscreen.

        The LayoutManager should call addPosition foreach item to be prepared, and these positions will have their ViewHolders created andbound, if there is sufficient time available, in advance of being needed by ascroll or layout.

        Parameters:
        adapterItemCount - number of items in the associated adapter.
        layoutPrefetchRegistry - PrefetchRegistry to add prefetch entries into.

      • isAttachedToWindow

         boolean isAttachedToWindow()

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

      • 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.

        Parameters:
        action - The Runnable that will be executed.

      • 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.

        Parameters:
        action - The Runnable to remove from the message handling queue

      • onAttachedToWindow

        @CallSuper() void onAttachedToWindow(RecyclerView view)

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

        If the RecyclerView is re-attached with the same LayoutManager and Adapter, it may notcall onLayoutChildren if nothing has changed and a layout wasnot requested on the RecyclerView while it was detached.

        Subclass implementations should always call through to the superclass implementation.

        Parameters:
        view - The RecyclerView this LayoutManager is bound to

      • onDetachedFromWindow

        @CallSuper() void onDetachedFromWindow(RecyclerView view, RecyclerView.Recycler recycler)

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

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

        If the RecyclerView is re-attached with the same LayoutManager and Adapter, it may notcall onLayoutChildren if nothing has changed and a layout wasnot requested on the RecyclerView while it was detached.

        If your LayoutManager has View references that it cleans in on-detach, it should alsocall requestLayout to ensure that it is re-laid out whenRecyclerView is re-attached.

        Subclass implementations should always call through to the superclass implementation.

        Parameters:
        view - The RecyclerView this LayoutManager is bound to
        recycler - The recycler to use if you prefer to recycle your children instead ofkeeping them around.

      • getClipToPadding

         boolean getClipToPadding()

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

      • 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 simpleitem animations are enabled. This means that add/remove operations on theadapter will result in animations to add new or appearing items, removed ordisappearing items, and moved items. If a LayoutManager returns false from supportsPredictiveItemAnimations, which is the default, and runs anormal layout operation during onLayoutChildren, theRecyclerView will have enough information to run those animations in a simpleway. For example, the default ItemAnimator, DefaultItemAnimator, willsimply fade views in and out, whether they are actually added/removed or whetherthey are moved on or off the screen due to other add/remove operations.

        A LayoutManager wanting a better item animation experience, where items can beanimated onto and off of the screen according to where the items exist when theyare not on screen, then the LayoutManager should return true from supportsPredictiveItemAnimations and add additional logic to onLayoutChildren. Supporting predictive animationsmeans that onLayoutChildren will be called twice;once as a "pre" layout step to determine where items would have been prior toa 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 outappropriately. Also, removed items willbe 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 usedto help calculate correct positioning of other views, including views thatwere not previously onscreen (referred to as APPEARING views), but whosepre-layout offscreen position can be determined given the extrainformation about the pre-layout removed views.

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

        The default LayoutManager implementations for RecyclerView handle all of theserequirements for animations already. Clients of RecyclerView can either use oneof these layout managers directly or look at their implementations ofonLayoutChildren() to see how they account for the APPEARING andDISAPPEARING views.

        Parameters:
        recycler - Recycler to use for fetching potentially cached views for aposition
        state - Transient state of RecyclerView

      • onLayoutCompleted

         void onLayoutCompleted(RecyclerView.State state)

        Called after a full layout calculation is finished. The layout calculation may includemultiple onLayoutChildren calls due to animations orlayout 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 scrollposition, saved state etc.

        Parameters:
        state - Transient state of RecyclerView

      • 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 typeand all values are within acceptable ranges. The default implementationreturns true for non-null params.

        Parameters:
        lp - LayoutParams object to check

      • 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.

        Parameters:
        dx - distance to scroll by in pixels.
        recycler - Recycler to use for fetching potentially cached views for aposition
        state - Transient state of RecyclerView

      • 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.

        Parameters:
        dy - distance to scroll in pixels.
        recycler - Recycler to use for fetching potentially cached views for aposition
        state - Transient state of RecyclerView

      • canScrollHorizontally

         boolean canScrollHorizontally()

        Query if horizontal scrolling is currently supported. The default implementationreturns false.

      • canScrollVertically

         boolean canScrollVertically()

        Query if vertical scrolling is currently supported. The default implementationreturns false.

      • scrollToPosition

         void scrollToPosition(int position)

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

        Parameters:
        position - Scroll to this adapter position.

      • 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 SmoothScroller instance and call startSmoothScroll.

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

      • startSmoothScroll

         void startSmoothScroll(RecyclerView.SmoothScroller smoothScroller)

        Starts a smooth scroll using the provided SmoothScroller.

        Each instance of SmoothScroller is intended to only be used once. Provide a newSmoothScroller instance each time this method is called.

        Calling this method will cancel any previous smooth scroll request.

        Parameters:
        smoothScroller - Instance which defines how smooth scroll should be animated

      • getLayoutDirection

         int getLayoutDirection()

        Returns the resolved layout direction for this RecyclerView.

      • endAnimation

         void endAnimation(View view)

        Ends all animations on the view created by the ItemAnimator.

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

      • addDisappearingView

         void addDisappearingView(View child)

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

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

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

      • addDisappearingView

         void addDisappearingView(View child, int index)

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

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

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

      • addView

         void addView(View child)

        Add a view to the currently attached RecyclerView if needed. LayoutManagers shoulduse this method to add views obtained from a Recycler using getViewForPosition.

        Parameters:
        child - View to add

      • addView

         void addView(View child, int index)

        Add a view to the currently attached RecyclerView if needed. LayoutManagers shoulduse this method to add views obtained from a Recycler using getViewForPosition.

        Parameters:
        child - View to add
        index - Index to add child at

      • removeView

         void removeView(View child)

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

        Parameters:
        child - View to remove

      • removeViewAt

         void removeViewAt(int index)

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

        Parameters:
        index - Index of the child view to remove

      • removeAllViews

         void removeAllViews()

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

      • getBaseline

         int getBaseline()

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

      • getPosition

         int getPosition(@NonNull() View view)

        Returns the adapter position of the item represented by the given View. This does notcontain any adapter changes that might have happened after the last layout.

        Parameters:
        view - The view to query

      • getItemViewType

         int getItemViewType(@NonNull() View view)

        Returns the View type defined by the adapter.

        Parameters:
        view - The view to query

      • findContainingItemView

        @Nullable() View findContainingItemView(@NonNull() View view)

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

        Note that this method may return null if the view is a child of the RecyclerView butnot a child of the LayoutManager (e.g. running a disappear animation).

        Parameters:
        view - The view that is a descendant of the LayoutManager.

      • findViewByPosition

        @Nullable() 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 aboutchild views.

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

        Parameters:
        position - Position of the item in adapter

      • detachView

         void detachView(@NonNull() View child)

        Temporarily detach a child view.

        LayoutManagers may want to perform a lightweight detach operation to rearrangeviews currently attached to the RecyclerView. Generally LayoutManager implementationswill 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 viewbefore the LayoutManager entry point method called by RecyclerView returns.

        Parameters:
        child - Child to detach

      • detachViewAt

         void detachViewAt(int index)

        Temporarily detach a child view.

        LayoutManagers may want to perform a lightweight detach operation to rearrangeviews currently attached to the RecyclerView. Generally LayoutManager implementationswill 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 viewbefore the LayoutManager entry point method called by RecyclerView returns.

        Parameters:
        index - Index of the child to detach

      • attachView

         void attachView(@NonNull() View child, int index)

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

        Parameters:
        child - Child to reattach
        index - Intended child index for child

      • moveView

         void moveView(int fromIndex, int toIndex)

        Moves a View from one position to another.

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

      • detachAndScrapView

         void detachAndScrapView(@NonNull() View child, @NonNull() 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 ordifferent data.

        Parameters:
        child - Child to detach and scrap
        recycler - Recycler to deposit the new scrap view into

      • detachAndScrapViewAt

         void detachAndScrapViewAt(int index, @NonNull() 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 ordifferent data.

        Parameters:
        index - Index of child to detach and scrap
        recycler - Recycler to deposit the new scrap view into

      • removeAndRecycleViewAt

         void removeAndRecycleViewAt(int index, @NonNull() RecyclerView.Recycler recycler)

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

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

      • 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.

      • getChildAt

        @Nullable() View getChildAt(int index)

        Return the child view at the given index

        Parameters:
        index - Index of child to return

      • 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.

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

      • 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.

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

      • getWidth

        @Px() 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 mayreflect the current MeasureSpec width if the LayoutManager is using AutoMeasure and the RecyclerView is in the process ofmeasuring. The LayoutManager must always use this method to retrieve the width relevantto it at any given time.

      • getHeight

        @Px() 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 mayreflect the current MeasureSpec height if the LayoutManager is using AutoMeasure and the RecyclerView is in the process ofmeasuring. The LayoutManager must always use this method to retrieve the height relevantto it at any given time.

      • getPaddingLeft

        @Px() int getPaddingLeft()

        Return the left padding of the parent RecyclerView

      • getPaddingTop

        @Px() int getPaddingTop()

        Return the top padding of the parent RecyclerView

      • getPaddingRight

        @Px() int getPaddingRight()

        Return the right padding of the parent RecyclerView

      • getPaddingBottom

        @Px() int getPaddingBottom()

        Return the bottom padding of the parent RecyclerView

      • getPaddingStart

        @Px() int getPaddingStart()

        Return the start padding of the parent RecyclerView

      • getPaddingEnd

        @Px() int getPaddingEnd()

        Return the end padding of the parent RecyclerView

      • isFocused

         boolean isFocused()

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

      • hasFocus

         boolean hasFocus()

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

      • offsetChildrenHorizontal

         void offsetChildrenHorizontal(@Px() int dx)

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

        Parameters:
        dx - Pixels to offset by

      • offsetChildrenVertical

         void offsetChildrenVertical(@Px() int dy)

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

        Parameters:
        dy - Pixels to offset by

      • ignoreView

         void ignoreView(@NonNull() 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 andrecyling. Methods like removeAndRecycleAllViews will ignore the childwhereas removeAllViews or offsetChildrenHorizontal will notignore 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.

        Parameters:
        view - View to ignore.

      • stopIgnoringView

         void stopIgnoringView(@NonNull() 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.

        Parameters:
        view - View to ignore.

      • detachAndScrapAttachedViews

         void detachAndScrapAttachedViews(@NonNull() RecyclerView.Recycler recycler)

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

        Parameters:
        recycler - Recycler to scrap views into

      • measureChild

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

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

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

        Parameters:
        child - Child view to measure
        widthUsed - Width in pixels currently consumed by other views, if relevant
        heightUsed - Height in pixels currently consumed by other views, if relevant

      • isMeasurementCacheEnabled

         boolean isMeasurementCacheEnabled()

        In addition to the View Framework's measurement cache, RecyclerView uses its ownadditional measurement cache for its children to avoid re-measuring them when notnecessary. It is on by default but it can be turned off via setMeasurementCacheEnabled.

      • setMeasurementCacheEnabled

         void setMeasurementCacheEnabled(boolean measurementCacheEnabled)

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

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

      • measureChildWithMargins

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

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

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

        Parameters:
        child - Child view to measure
        widthUsed - Width in pixels currently consumed by other views, if relevant
        heightUsed - Height in pixels currently consumed by other views, if relevant

      • getChildMeasureSpec

        @Deprecated() static int getChildMeasureSpec(int parentSize, int padding, int childDimension, boolean canScroll)

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

        Parameters:
        parentSize - Size of the parent view where the child will be placed
        padding - Total space currently consumed by other elements of the parent
        childDimension - Desired size of the child view, or MATCH_PARENT/WRAP_CONTENT.
        canScroll - true if the parent RecyclerView can scroll in this dimension

      • getChildMeasureSpec

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

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

        Parameters:
        parentSize - Size of the parent view where the child will be placed
        parentMode - The measurement spec mode of the parent
        padding - Total space currently consumed by other elements of parent
        childDimension - Desired size of the child view, or MATCH_PARENT/WRAP_CONTENT.
        canScroll - true if the parent RecyclerView can scroll in this dimension

      • getTransformedBoundingBox

         void getTransformedBoundingBox(@NonNull() View child, boolean includeDecorInsets, @NonNull() 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 {@code includeDecorInsets} is {@code true}, they are applied first before applyingthe View's matrix so that the decor offsets also go through the same transformation.

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

      • getDecoratedBoundsWithMargins

         void getDecoratedBoundsWithMargins(@NonNull() View view, @NonNull() Rect outBounds)

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

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

      • calculateItemDecorationsForChild

         void calculateItemDecorationsForChild(@NonNull() View child, @NonNull() Rect outRect)

        Calculates the item decor insets applied to the given child and updates the providedRect 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'smeasure child methods is called. If you need to measure the child with custom specs via measure, you can use this method to get decorations.

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

      • onFocusSearchFailed

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

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

        This is the LayoutManager's opportunity to populate views in the given directionto fulfill the request if it can. The LayoutManager should attach and returnthe 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 returnsthe next unfocusable view to become visible on the screen. This unfocusable view istypically the first view that's either partially or fully out of RV's padded boundedarea in the given direction. The default implementation returns null.

        Parameters:
        focused - The currently focused view
        direction - One of FOCUS_UP, FOCUS_DOWN,FOCUS_LEFT, FOCUS_RIGHT,FOCUS_BACKWARD, FOCUS_FORWARD or 0 for not applicable
        recycler - The recycler to use for obtaining views for currently offscreen items
        state - Transient state of RecyclerView

      • onInterceptFocusSearch

        @Nullable() View onInterceptFocusSearch(@NonNull() View focused, int direction)

        This method gives a LayoutManager an opportunity to intercept the initial focus searchbefore the default behavior of FocusFinder is used. If this method returnsnull FocusFinder will attempt to find a focusable child view. If it failsthen onFocusSearchFailed will be called to give the LayoutManager an opportunity to add new views for itemsthat did not have attached views representing them. The LayoutManager should not addor remove views from this method.

        Parameters:
        focused - The currently focused view
        direction - One of FOCUS_UP, FOCUS_DOWN,FOCUS_LEFT, FOCUS_RIGHT,FOCUS_BACKWARD, FOCUS_FORWARD

      • requestChildRectangleOnScreen

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

        Called when a child of the RecyclerView wants a particular rectangle to be positionedonto the screen. See requestChildRectangleOnScreen for more details.

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

        Parameters:
        child - The direct child making the request.
        rect - The rectangle in the child's coordinates the childwishes to be on the screen.
        immediate - True to forbid animated or delayed scrolling,false otherwise

      • requestChildRectangleOnScreen

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

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

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

      • isViewPartiallyVisible

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

        Returns whether the given child view is partially or fully visible within the paddedbounded 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 partiallyvisible if it's located outside RV's bounds and it's hitting either RV's start or endbounds.

        Parameters:
        child - The child view to be examined.
        completelyVisible - If true, the method returns true if and only if thechild iscompletely visible.
        acceptEndPointInclusion - If the view's endpoint intersection with RV's start of endbounds is enough to consider it partially visible,false otherwise.

      • onRequestChildFocus

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

        Called when a descendant view of the RecyclerView requests focus.

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

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

        Parameters:
        parent - The RecyclerView hosting this LayoutManager
        state - Current state of RecyclerView
        child - Direct child of the RecyclerView containing the newly focused view
        focused - The newly focused view.

      • onAdapterChanged

         void onAdapterChanged(@Nullable() RecyclerView.Adapter oldAdapter, @Nullable() RecyclerView.Adapter newAdapter)

        Called if the RecyclerView this LayoutManager is bound to has a different adapter set via setAdapter or swapAdapter. The LayoutManager may use thisopportunity to clear caches and configure state such that it can relayout appropriatelywith the new data and potentially new view types.

        The default implementation removes all currently attached views.

        Parameters:
        oldAdapter - The previous adapter instance.
        newAdapter - The new adapter instance.

      • onAddFocusables

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

        Called to populate focusable views within the RecyclerView.

        The LayoutManager implementation should return true if the defaultbehavior of addFocusables should besuppressed.

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

        Parameters:
        recyclerView - The RecyclerView hosting this LayoutManager
        views - List of output views.
        direction - One of FOCUS_UP, FOCUS_DOWN,FOCUS_LEFT, FOCUS_RIGHT,FOCUS_BACKWARD, FOCUS_FORWARD
        focusableMode - The type of focusables to be added.

      • onItemsAdded

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

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

      • onItemsRemoved

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

        Called when items have been removed from the adapter.

      • onItemsUpdated

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

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

      • onItemsMoved

         void onItemsMoved(@NonNull() 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/MOVEoperation. This callback is only called if and only if notifyItemMoved is called.

      • onMeasure

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

        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 standardmeasure cases including when the RecyclerView's layout_width or layout_height have beenset to wrap_content. If isAutoMeasureEnabled is overridden to return true,this method should not be overridden.

        The default implementation will handle EXACTLY measurements and respectthe minimum width and height properties of the host RecyclerView if measuredas UNSPECIFIED. AT_MOST measurements will be treated as EXACTLY and the RecyclerViewwill consume all available space.

        Parameters:
        recycler - Recycler
        state - Transient state of RecyclerView
        widthSpec - Width MeasureSpec
        heightSpec - Height MeasureSpec

      • onSaveInstanceState

        @Nullable() Parcelable onSaveInstanceState()

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

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

      • onRestoreInstanceState

         void onRestoreInstanceState(Parcelable state)

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

        Parameters:
        state - The parcelable that was returned by the previous LayoutManager'sonSaveInstanceState method.

      • onScrollStateChanged

         void onScrollStateChanged(int state)

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

        Parameters:
        state - The new scroll state for RecyclerView

      • removeAndRecycleAllViews

         void removeAndRecycleAllViews(@NonNull() 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.

        Parameters:
        recycler - Recycler to use to recycle children

      • requestSimpleAnimationsInNextLayout

         void requestSimpleAnimationsInNextLayout()

        A LayoutManager can call this method to force RecyclerView to run simple animations inthe next layout pass, even if there is not any trigger to do so. (e.g. adapter datachange).

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

      • getRowCountForAccessibility

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

        Returns the number of rows for accessibility.

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

        Parameters:
        recycler - The Recycler that can be used to convert view positions into adapterpositions
        state - The current state of RecyclerView

      • getColumnCountForAccessibility

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

        Returns the number of columns for accessibility.

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

        Parameters:
        recycler - The Recycler that can be used to convert view positions into adapterpositions
        state - The current state of RecyclerView

      • isLayoutHierarchical

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

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

        Default implementation returns false.

        Parameters:
        recycler - The Recycler that can be used to convert view positions into adapterpositions
        state - The current state of RecyclerView