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Callback

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

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

static Int

Public constructors

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

When finding views under a dragged view, by default, ItemTouchHelper searches for views that overlap with the dragged View.

open static ItemTouchUIUtil

Returns the ItemTouchUIUtil that is used by the Callback class for visual changes on Views in response to user interactions.

open Float

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).