WearableLinearLayoutManager

public class WearableLinearLayoutManager extends RecyclerView.LayoutManager, LinearLayoutManager implements ItemTouchHelper.ViewDropHandler, RecyclerView.SmoothScroller.ScrollVectorProvider


This wear-specific implementation of LinearLayoutManager provides basic offsetting logic for updating child layout. For round devices it offsets the children horizontally to make them appear to travel around a circle. For square devices it aligns them in a straight list. This functionality is provided by the CurvingLayoutCallback which is set when constructing the this class with its default constructor WearableLinearLayoutManager.

Summary

Nested types

WearableLinearLayoutManager.LayoutCallback

Callback for interacting with layout passes.

Public constructors

Creates a WearableLinearLayoutManager for a vertical list.

Creates a WearableLinearLayoutManager for a vertical list.

Public methods

@Nullable WearableLinearLayoutManager.LayoutCallback
@Override @NonNull void

Lay out all relevant child views from the given adapter.

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

Scroll vertically by dy pixels in screen coordinates and return the distance traveled.

@NonNull void

Set a particular instance of the layout callback for this WearableLinearLayoutManager.

Inherited methods

From class LinearLayoutManager
@Override @NonNull void

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

@Override @NonNull boolean
@Override @NonNull boolean
@Override @NonNull void
collectAdjacentPrefetchPositions(
    @NonNull int dx,
    @NonNull int dy,
    @NonNull RecyclerView.State state,
    @NonNull RecyclerView.LayoutManager.LayoutPrefetchRegistry layoutPrefetchRegistry
)

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

@Override @NonNull void
collectInitialPrefetchPositions(
    @NonNull int adapterItemCount,
    @NonNull 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.

@Override @NonNull int

Override this method if you want to support scroll bars.

@Override @NonNull int

Override this method if you want to support scroll bars.

@Override @NonNull int

Override this method if you want to support scroll bars.

@Override @NonNull PointF

Should calculate the vector that points to the direction where the target position can be found.

@Override @NonNull int

Override this method if you want to support scroll bars.

@Override @NonNull int

Override this method if you want to support scroll bars.

@Override @NonNull int

Override this method if you want to support scroll bars.

@NonNull int

Returns the adapter position of the first fully visible view.

@NonNull int

Returns the adapter position of the first visible view.

@NonNull int

Returns the adapter position of the last fully visible view.

@NonNull int

Returns the adapter position of the last visible view.

@Override @NonNull View
findViewByPosition(@NonNull int position)

Finds the view which represents the given adapter position.

@Override @NonNull RecyclerView.LayoutParams

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

@NonNull int

Gets the number of items to prefetch in collectInitialPrefetchPositions, which defines how many inner items should be prefetched when this LayoutManager's RecyclerView is nested inside another RecyclerView.

@RecyclerView.Orientation @NonNull int

Returns the current orientation of the layout.

@NonNull boolean

Returns whether LayoutManager will recycle its children when it is detached from RecyclerView.

@NonNull boolean

Returns if views are laid out from the opposite direction of the layout.

@NonNull boolean
@Override @NonNull boolean

Returns whether the measuring pass of layout should use the AutoMeasure mechanism of RecyclerView or if it should be done by the LayoutManager's implementation of onMeasure.

@NonNull boolean

Returns the current state of the smooth scrollbar feature.

@Override @NonNull void

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

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

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

@Override @NonNull void
@Override @NonNull void

Called after a full layout calculation is finished.

@Override @NonNull void

Called when the RecyclerView is ready to restore the state based on a previous RecyclerView.

@Override @NonNull Parcelable

Called when the LayoutManager should save its state.

@Override @NonNull void
prepareForDrop(
    @NonNull View view,
    @NonNull View target,
    @NonNull int x,
    @NonNull int y
)

Called by the after a View is dropped over another View.

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

Scroll horizontally by dx pixels in screen coordinates and return the distance traveled.

@Override @NonNull void
scrollToPosition(@NonNull int position)

Scroll the RecyclerView to make the position visible.

@NonNull void
scrollToPositionWithOffset(@NonNull int position, @NonNull int offset)

Scroll to the specified adapter position with the given offset from resolved layout start.

@NonNull void

Sets the number of items to prefetch in collectInitialPrefetchPositions, which defines how many inner items should be prefetched when this LayoutManager's RecyclerView is nested inside another RecyclerView.

@NonNull void

Sets the orientation of the layout.

@NonNull void
setRecycleChildrenOnDetach(@NonNull boolean recycleChildrenOnDetach)

Set whether LayoutManager will recycle its children when it is detached from RecyclerView.

@NonNull void
setReverseLayout(@NonNull boolean reverseLayout)

Used to reverse item traversal and layout order.

@NonNull void

When smooth scrollbar is enabled, the position and size of the scrollbar thumb is computed based on the number of visible pixels in the visible items.

@NonNull void
setStackFromEnd(@NonNull boolean stackFromEnd)

Compatibility support for setStackFromBottom

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

Smooth scroll to the specified adapter position.

@Override @NonNull boolean

Returns whether this LayoutManager supports "predictive item animations".

From class RecyclerView.LayoutManager
@NonNull void

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

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

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

@NonNull void

Add a view to the currently attached RecyclerView if needed.

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

Add a view to the currently attached RecyclerView if needed.

@NonNull void

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

@NonNull void

Reattach a previously detached view.

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

Reattach a previously detached view.

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

Reattach a previously detached view.

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

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

@NonNull boolean

Determines the validity of the supplied LayoutParams object.

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

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

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

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

@NonNull void
collectInitialPrefetchPositions(
    @NonNull int adapterItemCount,
    @NonNull 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.

@NonNull int

Override this method if you want to support scroll bars.

@NonNull int

Override this method if you want to support scroll bars.

@NonNull int

Override this method if you want to support scroll bars.

@NonNull int

Override this method if you want to support scroll bars.

@NonNull int

Override this method if you want to support scroll bars.

@NonNull int

Override this method if you want to support scroll bars.

@NonNull void

Temporarily detach and scrap all currently attached child views.

@NonNull void
detachAndScrapView(
    @NonNull View child,
    @NonNull RecyclerView.Recycler recycler
)

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

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

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

@NonNull void

Temporarily detach a child view.

@NonNull void
detachViewAt(@NonNull int index)

Temporarily detach a child view.

@NonNull void

Ends all animations on the view created by the ItemAnimator.

@Nullable View

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

@NonNull RecyclerView.LayoutParams

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

@NonNull RecyclerView.LayoutParams

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

@NonNull int

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

@NonNull int

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

@Nullable View
getChildAt(@NonNull int index)

Return the child view at the given index

@NonNull int

Return the current number of child views attached to the parent RecyclerView.

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

This method is deprecated.

use getChildMeasureSpec

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

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

@NonNull boolean

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

@NonNull int

Returns the number of columns for accessibility.

@NonNull int

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

@NonNull void

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

@NonNull int

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

@NonNull int

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

@NonNull int

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

@NonNull int

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

@NonNull int

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

@Nullable View

Returns the item View which has or contains focus.

@Px @NonNull int

Returns the height that is currently relevant to the LayoutManager.

@NonNull int

Return the height measurement spec mode that is currently relevant to the LayoutManager.

@NonNull int

Returns the number of items in the adapter bound to the parent RecyclerView.

@NonNull int

Returns the View type defined by the adapter.

@NonNull int

Returns the resolved layout direction for this RecyclerView.

@NonNull int

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

@Px @NonNull int
@Px @NonNull int
@Px @NonNull int

Return the bottom padding of the parent RecyclerView

@Px @NonNull int

Return the end padding of the parent RecyclerView

@Px @NonNull int

Return the left padding of the parent RecyclerView

@Px @NonNull int

Return the right padding of the parent RecyclerView

@Px @NonNull int

Return the start padding of the parent RecyclerView

@Px @NonNull int

Return the top padding of the parent RecyclerView

@NonNull int

Returns the adapter position of the item represented by the given View.

static @NonNull RecyclerView.LayoutManager.Properties
getProperties(
    @NonNull Context context,
    @Nullable AttributeSet attrs,
    @NonNull int defStyleAttr,
    @NonNull int defStyleRes
)

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

@NonNull int

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

@NonNull int

Returns the number of rows for accessibility.

@NonNull int

Returns the selection mode for accessibility.

@NonNull int

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

@NonNull void
getTransformedBoundingBox(
    @NonNull View child,
    @NonNull 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.

@Px @NonNull int

Returns the width that is currently relevant to the LayoutManager.

@NonNull int

Return the width measurement spec mode that is currently relevant to the LayoutManager.

@NonNull boolean

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

@NonNull void

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

@NonNull boolean

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

@NonNull boolean

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

final @NonNull boolean

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

@NonNull boolean

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

@NonNull boolean

In addition to the View Framework's measurement cache, RecyclerView uses its own additional measurement cache for its children to avoid re-measuring them when not necessary.

@NonNull boolean
@NonNull boolean
isViewPartiallyVisible(
    @NonNull View child,
    @NonNull boolean completelyVisible,
    @NonNull 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.

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

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

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

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

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

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

@NonNull void
measureChildWithMargins(
    @NonNull View child,
    @NonNull int widthUsed,
    @NonNull 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.

@NonNull void
moveView(@NonNull int fromIndex, @NonNull int toIndex)

Moves a View from one position to another.

@NonNull void

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

@NonNull void

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

@NonNull void

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

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

Called to populate focusable views within the RecyclerView.

@CallSuper @NonNull void

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

@NonNull void

This method is deprecated.

override onDetachedFromWindow

@CallSuper @NonNull void

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

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

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

@NonNull void
@NonNull void

Called by the accessibility delegate to initialize an accessibility event.

@NonNull void

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

@NonNull void

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

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

This method gives a LayoutManager an opportunity to intercept the initial focus search before the default behavior of FocusFinder is used.

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

Called when items have been added to the adapter.

@NonNull void

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

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

Called when an item is moved withing the adapter.

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

Called when items have been removed from the adapter.

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

Called when items have been changed in the adapter.

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

Called when items have been changed in the adapter and with optional payload.

@NonNull void

Lay out all relevant child views from the given adapter.

@NonNull void

Called after a full layout calculation is finished.

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

Measure the attached RecyclerView.

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

This method is deprecated.

Use onRequestChildFocus

@NonNull 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.

@NonNull void

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

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

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

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

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

@NonNull void

Causes the Runnable to execute on the next animation time step.

@NonNull void

Remove all views from the currently attached RecyclerView.

@NonNull void

Removes all views and recycles them using the given recycler.

@NonNull void
removeAndRecycleView(
    @NonNull View child,
    @NonNull RecyclerView.Recycler recycler
)

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

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

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

@NonNull boolean

Removes the specified Runnable from the message queue.

@NonNull void

Finish removing a view that was previously temporarily detached.

@NonNull void

Remove a view from the currently attached RecyclerView if needed.

@NonNull void
removeViewAt(@NonNull int index)

Remove a view from the currently attached RecyclerView if needed.

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

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

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

Requests that the given child of the RecyclerView be positioned onto the screen.

@NonNull void

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

@NonNull void

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.

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

Scroll horizontally by dx pixels in screen coordinates and return the distance traveled.

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

Scroll vertically by dy pixels in screen coordinates and return the distance traveled.

@NonNull void
setAutoMeasureEnabled(@NonNull boolean enabled)

This method is deprecated.

Implementors of LayoutManager should define whether or not it uses AutoMeasure by overriding isAutoMeasureEnabled.

final @NonNull void
setItemPrefetchEnabled(@NonNull boolean enabled)

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

@NonNull void
setMeasuredDimension(@NonNull int widthSize, @NonNull int heightSize)

Set the measured dimensions of the host RecyclerView.

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

Sets the measured dimensions from the given bounding box of the children and the measurement specs that were passed into onMeasure.

@NonNull void
setMeasurementCacheEnabled(@NonNull boolean measurementCacheEnabled)

Sets whether RecyclerView should use its own measurement cache for the children.

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

Smooth scroll to the specified adapter position.

@NonNull void

Starts a smooth scroll using the provided SmoothScroller.

@NonNull void

View can be scrapped and recycled again.

Public constructors

WearableLinearLayoutManager

public WearableLinearLayoutManager(@NonNull Context context)

Creates a WearableLinearLayoutManager for a vertical list.

Parameters
@NonNull Context context

Current context, will be used to access resources.

WearableLinearLayoutManager

public WearableLinearLayoutManager(
    @NonNull Context context,
    @NonNull WearableLinearLayoutManager.LayoutCallback layoutCallback
)

Creates a WearableLinearLayoutManager for a vertical list.

Parameters
@NonNull Context context

Current context, will be used to access resources.

@NonNull WearableLinearLayoutManager.LayoutCallback layoutCallback

Callback to be associated with this WearableLinearLayoutManager

Public methods

onLayoutChildren

@Override
@NonNull
public @Override void onLayoutChildren(
    @NonNull RecyclerView.Recycler recycler,
    @NonNull 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 #getItemAnimator() 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, , 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, LayoutParams#isItemRemoved() 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.

scrollVerticallyBy

@Override
@NonNull
public @Override int scrollVerticallyBy(
    @NonNull int dy,
    @NonNull RecyclerView.Recycler recycler,
    @NonNull RecyclerView.State state
)

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

setLayoutCallback

@NonNull
public void setLayoutCallback(
    @Nullable WearableLinearLayoutManager.LayoutCallback layoutCallback
)

Set a particular instance of the layout callback for this WearableLinearLayoutManager. The callback will be called on the Ui thread.