GridLayoutManager

fun canScrollHorizontally(): Boolean

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

fun canScrollVertically(): Boolean

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

fun checkLayoutParams(lp: RecyclerView.LayoutParams?): Boolean

Determines the validity of the supplied LayoutParams object.

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

fun collectAdjacentPrefetchPositions(
    dx: Int,
    dy: Int,
    state: RecyclerView.State,
    layoutPrefetchRegistry: RecyclerView.LayoutManager.LayoutPrefetchRegistry
): Unit

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

If item prefetch is enabled, this method is called in between traversals to gather which positions the LayoutManager will soon need, given upcoming movement in subsequent traversals.

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

fun collectInitialPrefetchPositions(
    adapterItemCount: Int,
    layoutPrefetchRegistry: RecyclerView.LayoutManager.LayoutPrefetchRegistry
): Unit

Gather all positions from the LayoutManager to be prefetched in preperation for its RecyclerView to come on screen, due to the movement of another, containing RecyclerView.

This method is only called when a RecyclerView is nested in another RecyclerView.

If item prefetch is enabled for this LayoutManager, as well in another containing LayoutManager, this method is called in between draw traversals to gather which positions this LayoutManager will first need, once it appears on the screen.

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

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

fun generateDefaultLayoutParams(): RecyclerView.LayoutParams

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

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

fun generateLayoutParams(lp: ViewGroup.LayoutParams): RecyclerView.LayoutParams

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

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

fun generateLayoutParams(context: Context, attrs: AttributeSet): RecyclerView.LayoutParams

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

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

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

Returns the number of columns for accessibility.

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

fun getDecoratedBottom(child: View): Int

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

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

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

fun getDecoratedLeft(child: View): Int

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

fun getDecoratedRight(child: View): Int

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

fun getDecoratedTop(child: View): Int

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

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

Returns the number of rows for accessibility.

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

fun getViewCenter(child: View): Int

Returns calculated center of the child view in the parent BaseGridView. The value is calculated from item alignment settings. A default value is center of the child view.

fun getWindowKeyLine(): Int

Returns calculated offset in pixels for alignment key line. The value is calculated from BaseGridView's window alignment settings. A default value is center of the BaseGridView.

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

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

The default implementation removes all currently attached views.

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

Called to populate focusable views within the RecyclerView.

The LayoutManager implementation should return true if the default behavior of addFocusables should be suppressed.

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

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

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

Default implementation adds a androidx.core.view.accessibility.AccessibilityNodeInfoCompat.CollectionInfoCompat.

You should override getRowCountForAccessibility, getColumnCountForAccessibility, isLayoutHierarchical and getSelectionModeForAccessibility for more accurate accessibility information.

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

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

Default implementation adds basic positioning information about the item.

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

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

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

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

fun onItemsChanged(recyclerView: RecyclerView): Unit

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

fun onItemsMoved(
    recyclerView: RecyclerView,
    fromPosition: Int,
    toPosition: Int,
    itemCount: Int
): Unit

Called when an item is moved withing the adapter.

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

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

Called when items have been removed from the adapter.

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

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

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

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

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

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

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

fun onLayoutCompleted(state: RecyclerView.State): Unit

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

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

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

Measure the attached RecyclerView. Implementations must call setMeasuredDimension before returning.

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

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

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

Called when a descendant view of the RecyclerView requests focus.

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

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

fun onRestoreInstanceState(state: Parcelable?): Unit

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

fun onSaveInstanceState(): Parcelable

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

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

fun onScrollStateChanged(state: Int): Unit

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

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

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

fun removeAndRecycleAllViews(recycler: RecyclerView.Recycler): Unit

Removes all views and recycles them using the given recycler.

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

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

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

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

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

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

fun scrollToPosition(position: Int): Unit

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

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

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

fun setFocusOutAllowed(throughFront: Boolean, throughBack: Boolean): Unit

Sets whether focus can move out from the front and/or back of the grid view.

fun setOrientation(orientation: Int): Unit

Sets grid view orientation.

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

Smooth scroll to the specified adapter position.

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

fun startSmoothScroll(smoothScroller: RecyclerView.SmoothScroller): Unit

Starts a smooth scroll using the provided SmoothScroller.

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

Calling this method will cancel any previous smooth scroll request.

fun supportsPredictiveItemAnimations(): Boolean

Returns whether this LayoutManager supports "predictive item animations".

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

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

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.