Callback

Kotlin |Java

abstract class Callback

kotlin.Any
↳	androidx.recyclerview.widget.ItemTouchHelper.Callback

Known Direct Subclasses ItemTouchHelper.SimpleCallback ItemTouchHelper.SimpleCallback A simple wrapper to the default Callback which you can construct with drag and swipe directions and this class will handle the flag callbacks.

This class is the contract between ItemTouchHelper and your application. It lets you control which touch behaviors are enabled per each ViewHolder and also receive callbacks when user performs these actions.

To control which actions user can take on each view, you should override getMovementFlags(RecyclerView, ViewHolder) and return appropriate set of direction flags. (LEFT, RIGHT, START, END, UP, DOWN). You can use makeMovementFlags(int, int) to easily construct it. Alternatively, you can use SimpleCallback.

If user drags an item, ItemTouchHelper will call onMove(recyclerView, dragged, target). Upon receiving this callback, you should move the item from the old position (dragged.getAdapterPosition()) to new position (target.getAdapterPosition()) in your adapter and also call RecyclerView.Adapter#notifyItemMoved(int, int). To control where a View can be dropped, you can override canDropOver(RecyclerView, ViewHolder, ViewHolder). When a dragging View overlaps multiple other views, Callback chooses the closest View with which dragged View might have changed positions. Although this approach works for many use cases, if you have a custom LayoutManager, you can override chooseDropTarget(ViewHolder, java.util.List, int, int) to select a custom drop target.

When a View is swiped, ItemTouchHelper animates it until it goes out of bounds, then calls onSwiped(ViewHolder, int). At this point, you should update your adapter (e.g. remove the item) and call related Adapter#notify event.

Summary

Constants
static Int	DEFAULT_DRAG_ANIMATION_DURATION
static Int	DEFAULT_SWIPE_ANIMATION_DURATION

Public constructors
<init>() This class is the contract between ItemTouchHelper and your application.

Public methods
open Boolean	canDropOver(@NonNull recyclerView: RecyclerView, @NonNull current: RecyclerView.ViewHolder, @NonNull target: RecyclerView.ViewHolder) Return true if the current ViewHolder can be dropped over the the target ViewHolder.
open RecyclerView.ViewHolder!	chooseDropTarget(@NonNull selected: RecyclerView.ViewHolder, @NonNull dropTargets: MutableList<RecyclerView.ViewHolder!>, curX: Int, curY: Int) Called by ItemTouchHelper to select a drop target from the list of ViewHolders that are under the dragged View.
open Unit	clearView(@NonNull recyclerView: RecyclerView, @NonNull viewHolder: RecyclerView.ViewHolder) Called by the ItemTouchHelper when the user interaction with an element is over and it also completed its animation.
open Int	convertToAbsoluteDirection(flags: Int, layoutDirection: Int) Converts a given set of flags to absolution direction which means START and END are replaced with LEFT and RIGHT depending on the layout direction.
open static Int	convertToRelativeDirection(flags: Int, layoutDirection: Int) Replaces a movement direction with its relative version by taking layout direction into account.
open Long	getAnimationDuration(@NonNull recyclerView: RecyclerView, animationType: Int, animateDx: Float, animateDy: Float) Called by the ItemTouchHelper when user action finished on a ViewHolder and now the View will be animated to its final position.
open Int	getBoundingBoxMargin() When finding views under a dragged view, by default, ItemTouchHelper searches for views that overlap with the dragged View.
open static ItemTouchUIUtil	getDefaultUIUtil() Returns the ItemTouchUIUtil that is used by the Callback class for visual changes on Views in response to user interactions.
open Float	getMoveThreshold(@NonNull viewHolder: RecyclerView.ViewHolder) Returns the fraction that the user should move the View to be considered as it is dragged.
abstract Int	getMovementFlags(@NonNull recyclerView: RecyclerView, @NonNull viewHolder: RecyclerView.ViewHolder) Should return a composite flag which defines the enabled move directions in each state (idle, swiping, dragging).
open Float	getSwipeEscapeVelocity(defaultValue: Float) Defines the minimum velocity which will be considered as a swipe action by the user.
open Float	getSwipeThreshold(@NonNull viewHolder: RecyclerView.ViewHolder) Returns the fraction that the user should move the View to be considered as swiped.
open Float	getSwipeVelocityThreshold(defaultValue: Float) Defines the maximum velocity ItemTouchHelper will ever calculate for pointer movements.
open Int	interpolateOutOfBoundsScroll(@NonNull recyclerView: RecyclerView, viewSize: Int, viewSizeOutOfBounds: Int, totalSize: Int, msSinceStartScroll: Long) Called by the ItemTouchHelper when user is dragging a view out of bounds.
open Boolean	isItemViewSwipeEnabled() Returns whether ItemTouchHelper should start a swipe operation if a pointer is swiped over the View.
open Boolean	isLongPressDragEnabled() Returns whether ItemTouchHelper should start a drag and drop operation if an item is long pressed.
open static Int	makeFlag(actionState: Int, directions: Int) Shifts the given direction flags to the offset of the given action state.
open static Int	makeMovementFlags(dragFlags: Int, swipeFlags: Int) Convenience method to create movement flags.
open Unit	onChildDraw(@NonNull c: Canvas, @NonNull recyclerView: RecyclerView, @NonNull viewHolder: RecyclerView.ViewHolder, dX: Float, dY: Float, actionState: Int, isCurrentlyActive: Boolean) Called by ItemTouchHelper on RecyclerView's onDraw callback.
open Unit	onChildDrawOver(@NonNull c: Canvas, @NonNull recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder!, dX: Float, dY: Float, actionState: Int, isCurrentlyActive: Boolean) Called by ItemTouchHelper on RecyclerView's onDraw callback.
abstract Boolean	onMove(@NonNull recyclerView: RecyclerView, @NonNull viewHolder: RecyclerView.ViewHolder, @NonNull target: RecyclerView.ViewHolder) Called when ItemTouchHelper wants to move the dragged item from its old position to the new position.
open Unit	onMoved(@NonNull recyclerView: RecyclerView, @NonNull viewHolder: RecyclerView.ViewHolder, fromPos: