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: Int, @NonNull target: RecyclerView.ViewHolder, toPos: Int, x: Int, y: Int) Called when onMove(RecyclerView, ViewHolder, ViewHolder) returns true.
open Unit	onSelectedChanged(@Nullable viewHolder: RecyclerView.ViewHolder?, actionState: Int) Called when the ViewHolder swiped or dragged by the ItemTouchHelper is changed.
abstract Unit	onSwiped(@NonNull viewHolder: RecyclerView.ViewHolder, direction: Int) Called when a ViewHolder is swiped by the user.

Constants

DEFAULT_DRAG_ANIMATION_DURATION

static val DEFAULT_DRAG_ANIMATION_DURATION: Int

Value: 200

DEFAULT_SWIPE_ANIMATION_DURATION

static val DEFAULT_SWIPE_ANIMATION_DURATION: Int

Value: 250

Public constructors

<init>

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.

Public methods

canDropOver

open fun canDropOver(@NonNull recyclerView: RecyclerView, @NonNull current: RecyclerView.ViewHolder, @NonNull target: RecyclerView.ViewHolder): Boolean

Return true if the current ViewHolder can be dropped over the the target ViewHolder.

This method is used when selecting drop target for the dragged View. After Views are eliminated either via bounds check or via this method, resulting set of views will be passed to chooseDropTarget(ViewHolder, java.util.List, int, int).

Default implementation returns true.

Parameters
recyclerView	RecyclerView: The RecyclerView to which ItemTouchHelper is attached to.
current	RecyclerView: The ViewHolder that user is dragging.
target	RecyclerView: The ViewHolder which is below the dragged ViewHolder.

Return
Boolean: True if the dragged ViewHolder can be replaced with the target ViewHolder, false otherwise.

chooseDropTarget

open fun chooseDropTarget(@NonNull selected: RecyclerView.ViewHolder, @NonNull dropTargets: MutableList<RecyclerView.ViewHolder!>, curX: Int, curY: Int): RecyclerView.ViewHolder!

Called by ItemTouchHelper to select a drop target from the list of ViewHolders that are under the dragged View.

Default implementation filters the View with which dragged item have changed position in the drag direction. For instance, if the view is dragged UP, it compares the view.getTop() of the two views before and after drag started. If that value is different, the target view passes the filter.

Among these Views which pass the test, the one closest to the dragged view is chosen.

This method is called on the main thread every time user moves the View. If you want to override it, make sure it does not do any expensive operations.

Parameters
selected	RecyclerView.ViewHolder: The ViewHolder being dragged by the user.
dropTargets	RecyclerView.ViewHolder: The list of ViewHolder that are under the dragged View and candidate as a drop.
curX	RecyclerView.ViewHolder: The updated left value of the dragged View after drag translations are applied. This value does not include margins added by RecyclerView.ItemDecorations.
curY	RecyclerView.ViewHolder: The updated top value of the dragged View after drag translations are applied. This value does not include margins added by RecyclerView.ItemDecorations.

Return
RecyclerView.ViewHolder!: A ViewHolder to whose position the dragged ViewHolder should be moved to.

clearView

open fun clearView(@NonNull recyclerView: RecyclerView, @NonNull viewHolder: RecyclerView.ViewHolder): Unit

Called by the ItemTouchHelper when the user interaction with an element is over and it also completed its animation.

This is a good place to clear all changes on the View that was done in onSelectedChanged(RecyclerView.ViewHolder, int), onChildDraw(Canvas, RecyclerView, ViewHolder, float, float, int, * boolean) or onChildDrawOver(Canvas, RecyclerView, ViewHolder, float, float, int, boolean).

Parameters
recyclerView	RecyclerView: The RecyclerView which is controlled by the ItemTouchHelper.
viewHolder	RecyclerView: The View that was interacted by the user.

convertToAbsoluteDirection

open fun convertToAbsoluteDirection(flags: Int, layoutDirection: Int): 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.

Parameters
flags	Int: The flag value that include any number of movement flags.
layoutDirection	Int: The layout direction of the RecyclerView.

Return
Int: Updated flags which includes only absolute direction values.

convertToRelativeDirection

open static fun convertToRelativeDirection(flags: Int, layoutDirection: Int): Int

Replaces a movement direction with its relative version by taking layout direction into account.

Parameters
flags	Int: The flag value that include any number of movement flags.
layoutDirection	Int: The layout direction of the View. Can be obtained from ViewCompat#getLayoutDirection(android.view.View).

Return
Int: Updated flags which uses relative flags (START, END) instead of LEFT, RIGHT.

See Also

• #convertToAbsoluteDirection(int, int)

getAnimationDuration

open fun getAnimationDuration(@NonNull recyclerView: RecyclerView, animationType: Int, animateDx: Float, animateDy: Float): Long

Called by the ItemTouchHelper when user action finished on a ViewHolder and now the View will be animated to its final position.

Default implementation uses ItemAnimator's duration values. If animationType is ANIMATION_TYPE_DRAG, it returns RecyclerView.ItemAnimator#getMoveDuration(), otherwise, it returns RecyclerView.ItemAnimator#getRemoveDuration(). If RecyclerView does not have any RecyclerView.ItemAnimator attached, this method returns DEFAULT_DRAG_ANIMATION_DURATION or DEFAULT_SWIPE_ANIMATION_DURATION depending on the animation type.

Parameters
recyclerView	RecyclerView: The RecyclerView to which the ItemTouchHelper is attached to.
animationType	RecyclerView: The type of animation. Is one of ANIMATION_TYPE_DRAG, ANIMATION_TYPE_SWIPE_CANCEL or ANIMATION_TYPE_SWIPE_SUCCESS.
animateDx	RecyclerView: The horizontal distance that the animation will offset
animateDy	RecyclerView: The vertical distance that the animation will offset

Return
Long: The duration for the animation

getBoundingBoxMargin

open fun getBoundingBoxMargin(): Int

When finding views under a dragged view, by default, ItemTouchHelper searches for views that overlap with the dragged View. By overriding this method, you can extend or shrink the search box.

Return
Int: The extra margin to be added to the hit box of the dragged View.

getDefaultUIUtil

@NonNull open static fun getDefaultUIUtil(): ItemTouchUIUtil

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

By default, Callback applies these changes on RecyclerView.ViewHolder#itemView.

For example, if you have a use case where you only want the text to move when user swipes over the view, you can do the following:

public void clearView(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder){
                  getDefaultUIUtil().clearView(((ItemTouchViewHolder) viewHolder).textView);
              }
              public void onSelectedChanged(RecyclerView.ViewHolder viewHolder, int actionState) {
                  if (viewHolder != null){
                      getDefaultUIUtil().onSelected(((ItemTouchViewHolder) viewHolder).textView);
                  }
              }
              public void onChildDraw(Canvas c, RecyclerView recyclerView,
                      RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState,
                      boolean isCurrentlyActive) {
                  getDefaultUIUtil().onDraw(c, recyclerView,
                          ((ItemTouchViewHolder) viewHolder).textView, dX, dY,
                          actionState, isCurrentlyActive);
                  return true;
              }
              public void onChildDrawOver(Canvas c, RecyclerView recyclerView,
                      RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState,
                      boolean isCurrentlyActive) {
                  getDefaultUIUtil().onDrawOver(c, recyclerView,
                          ((ItemTouchViewHolder) viewHolder).textView, dX, dY,
                          actionState, isCurrentlyActive);
                  return true;
              }
          

Return
ItemTouchUIUtil: The ItemTouchUIUtil instance that is used by the Callback

getMoveThreshold

open fun getMoveThreshold(@NonNull viewHolder: RecyclerView.ViewHolder): Float

Returns the fraction that the user should move the View to be considered as it is dragged. After a view is moved this amount, ItemTouchHelper starts checking for Views below it for a possible drop.

Parameters
viewHolder	RecyclerView.ViewHolder: The ViewHolder that is being dragged.

Return
Float: A float value that denotes the fraction of the View size. Default value is .5f .

getMovementFlags

abstract fun getMovementFlags(@NonNull recyclerView: RecyclerView, @NonNull viewHolder: RecyclerView.ViewHolder): Int

Should return a composite flag which defines the enabled move directions in each state (idle, swiping, dragging).

Instead of composing this flag manually, you can use makeMovementFlags(int, * int) or makeFlag(int, int).

This flag is composed of 3 sets of 8 bits, where first 8 bits are for IDLE state, next 8 bits are for SWIPE state and third 8 bits are for DRAG state. Each 8 bit sections can be constructed by simply OR'ing direction flags defined in ItemTouchHelper.

For example, if you want it to allow swiping LEFT and RIGHT but only allow starting to swipe by swiping RIGHT, you can return:

makeFlag(ACTION_STATE_IDLE, RIGHT) | makeFlag(ACTION_STATE_SWIPE, LEFT | RIGHT);
          

This means, allow right movement while IDLE and allow right and left movement while swiping.

Parameters
recyclerView	RecyclerView: The RecyclerView to which ItemTouchHelper is attached.
viewHolder	RecyclerView: The ViewHolder for which the movement information is necessary.

Return
Int: flags specifying which movements are allowed on this ViewHolder.

See Also

• #makeMovementFlags(int, int)#makeFlag(int, int)

getSwipeEscapeVelocity

open fun getSwipeEscapeVelocity(defaultValue: Float): Float

Defines the minimum velocity which will be considered as a swipe action by the user.

You can increase this value to make it harder to swipe or decrease it to make it easier. Keep in mind that ItemTouchHelper also checks the perpendicular velocity and makes sure current direction velocity is larger then the perpendicular one. Otherwise, user's movement is ambiguous. You can change the threshold by overriding getSwipeVelocityThreshold(float).

The velocity is calculated in pixels per second.

The default framework value is passed as a parameter so that you can modify it with a multiplier.

Parameters
defaultValue	Float: The default value (in pixels per second) used by the ItemTouchHelper.

Return
Float: The minimum swipe velocity. The default implementation returns the defaultValue parameter.

See Also

• #getSwipeVelocityThreshold(float)#getSwipeThreshold(ViewHolder)

getSwipeThreshold

open fun getSwipeThreshold(@NonNull viewHolder: RecyclerView.ViewHolder): Float

Returns the fraction that the user should move the View to be considered as swiped. The fraction is calculated with respect to RecyclerView's bounds.

Default value is .5f, which means, to swipe a View, user must move the View at least half of RecyclerView's width or height, depending on the swipe direction.

Parameters
viewHolder	RecyclerView.ViewHolder: The ViewHolder that is being dragged.

Return
Float: A float value that denotes the fraction of the View size. Default value is .5f .

getSwipeVelocityThreshold

open fun getSwipeVelocityThreshold(defaultValue: Float): Float

Defines the maximum velocity ItemTouchHelper will ever calculate for pointer movements.

To consider a movement as swipe, ItemTouchHelper requires it to be larger than the perpendicular movement. If both directions reach to the max threshold, none of them will be considered as a swipe because it is usually an indication that user rather tried to scroll then swipe.

The velocity is calculated in pixels per second.

You can customize this behavior by changing this method. If you increase the value, it will be easier for the user to swipe diagonally and if you decrease the value, user will need to make a rather straight finger movement to trigger a swipe.

Parameters
defaultValue	Float: The default value(in pixels per second) used by the ItemTouchHelper.

Return
Float: The velocity cap for pointer movements. The default implementation returns the defaultValue parameter.

See Also

• #getSwipeEscapeVelocity(float)

interpolateOutOfBoundsScroll

open fun interpolateOutOfBoundsScroll(@NonNull recyclerView: RecyclerView, viewSize: Int, viewSizeOutOfBounds: Int, totalSize: Int, msSinceStartScroll: Long): Int

Called by the ItemTouchHelper when user is dragging a view out of bounds.

You can override this method to decide how much RecyclerView should scroll in response to this action. Default implementation calculates a value based on the amount of View out of bounds and the time it spent there. The longer user keeps the View out of bounds, the faster the list will scroll. Similarly, the larger portion of the View is out of bounds, the faster the RecyclerView will scroll.

Parameters
recyclerView	RecyclerView: The RecyclerView instance to which ItemTouchHelper is attached to.
viewSize	RecyclerView: The total size of the View in scroll direction, excluding item decorations.
viewSizeOutOfBounds	RecyclerView: The total size of the View that is out of bounds. This value is negative if the View is dragged towards left or top edge.
totalSize	RecyclerView: The total size of RecyclerView in the scroll direction.
msSinceStartScroll	RecyclerView: The time passed since View is kept out of bounds.

Return
Int: The amount that RecyclerView should scroll. Keep in mind that this value will be passed to RecyclerView#scrollBy(int, int) method.

isItemViewSwipeEnabled

open fun isItemViewSwipeEnabled(): Boolean

Returns whether ItemTouchHelper should start a swipe operation if a pointer is swiped over the View.

Default value returns true but you may want to disable this if you want to start swiping on a custom view touch using startSwipe(ViewHolder).

Return
Boolean: True if ItemTouchHelper should start swiping an item when user swipes a pointer over the View, false otherwise. Default value is true.

See Also

• #startSwipe(ViewHolder)

isLongPressDragEnabled

open fun isLongPressDragEnabled(): Boolean

Returns whether ItemTouchHelper should start a drag and drop operation if an item is long pressed.

Default value returns true but you may want to disable this if you want to start dragging on a custom view touch using startDrag(ViewHolder).

Return
Boolean: True if ItemTouchHelper should start dragging an item when it is long pressed, false otherwise. Default value is true.

See Also

• #startDrag(ViewHolder)

makeFlag

open static fun makeFlag(actionState: Int, directions: Int): Int

Shifts the given direction flags to the offset of the given action state.

Parameters
actionState	Int: The action state you want to get flags in. Should be one of ACTION_STATE_IDLE, ACTION_STATE_SWIPE or ACTION_STATE_DRAG.
directions	Int: The direction flags. Can be composed from UP, DOWN, RIGHT, LEFT START and END.

Return
Int: And integer that represents the given directions in the provided actionState.

makeMovementFlags

open static fun makeMovementFlags(dragFlags: Int, swipeFlags: Int): Int

Convenience method to create movement flags.

For instance, if you want to let your items be drag & dropped vertically and swiped left to be dismissed, you can call this method with: makeMovementFlags(UP | DOWN, LEFT);

Parameters
dragFlags	Int: The directions in which the item can be dragged.
swipeFlags	Int: The directions in which the item can be swiped.

Return
Int: Returns an integer composed of the given drag and swipe flags.

onChildDraw

open fun onChildDraw(@NonNull c: Canvas, @NonNull recyclerView: RecyclerView, @NonNull viewHolder: RecyclerView.ViewHolder, dX: Float, dY: Float, actionState: Int, isCurrentlyActive: Boolean): Unit

Called by ItemTouchHelper on RecyclerView's onDraw callback.

If you would like to customize how your View's respond to user interactions, this is a good place to override.

Default implementation translates the child by the given dX, dY. ItemTouchHelper also takes care of drawing the child after other children if it is being dragged. This is done using child re-ordering mechanism. On platforms prior to L, this is achieved via android.view.ViewGroup#getChildDrawingOrder(int, int) and on L and after, it changes View's elevation value to be greater than all other children.)

Parameters
c	Canvas: The canvas which RecyclerView is drawing its children
recyclerView	Canvas: The RecyclerView to which ItemTouchHelper is attached to
viewHolder	Canvas: The ViewHolder which is being interacted by the User or it was interacted and simply animating to its original position
dX	Canvas: The amount of horizontal displacement caused by user's action
dY	Canvas: The amount of vertical displacement caused by user's action
actionState	Canvas: The type of interaction on the View. Is either or ACTION_STATE_SWIPE.
isCurrentlyActive	Canvas: True if this view is currently being controlled by the user or false it is simply animating back to its original state.

See Also

• #onChildDrawOver(Canvas, RecyclerView, ViewHolder, float, float, int, * boolean)

onChildDrawOver

open fun onChildDrawOver(@NonNull c: Canvas, @NonNull recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder!, dX: Float, dY: Float, actionState: Int, isCurrentlyActive: Boolean): Unit

Called by ItemTouchHelper on RecyclerView's onDraw callback.

If you would like to customize how your View's respond to user interactions, this is a good place to override.

Default implementation translates the child by the given dX, dY. ItemTouchHelper also takes care of drawing the child after other children if it is being dragged. This is done using child re-ordering mechanism. On platforms prior to L, this is achieved via android.view.ViewGroup#getChildDrawingOrder(int, int) and on L and after, it changes View's elevation value to be greater than all other children.)

Parameters
c	Canvas: The canvas which RecyclerView is drawing its children
recyclerView	Canvas: The RecyclerView to which ItemTouchHelper is attached to
viewHolder	Canvas: The ViewHolder which is being interacted by the User or it was interacted and simply animating to its original position
dX	Canvas: The amount of horizontal displacement caused by user's action
dY	Canvas: The amount of vertical displacement caused by user's action
actionState	Canvas: The type of interaction on the View. Is either or ACTION_STATE_SWIPE.
isCurrentlyActive	Canvas: True if this view is currently being controlled by the user or false it is simply animating back to its original state.

See Also

• #onChildDrawOver(Canvas, RecyclerView, ViewHolder, float, float, int, * boolean)

onMove

abstract fun onMove(@NonNull recyclerView: RecyclerView, @NonNull viewHolder: RecyclerView.ViewHolder, @NonNull target: RecyclerView.ViewHolder): Boolean

Called when ItemTouchHelper wants to move the dragged item from its old position to the new position.

If this method returns true, ItemTouchHelper assumes viewHolder has been moved to the adapter position of target ViewHolder ( ViewHolder#getAdapterPosition()).

If you don't support drag & drop, this method will never be called.

Parameters
recyclerView	RecyclerView: The RecyclerView to which ItemTouchHelper is attached to.
viewHolder	RecyclerView: The ViewHolder which is being dragged by the user.
target	RecyclerView: The ViewHolder over which the currently active item is being dragged.

Return
Boolean: True if the viewHolder has been moved to the adapter position of target.

See Also

• #onMoved(RecyclerView, ViewHolder, int, ViewHolder, int, int, int)

onMoved

open fun onMoved(@NonNull recyclerView: RecyclerView, @NonNull viewHolder: RecyclerView.ViewHolder, fromPos: Int, @NonNull target: RecyclerView.ViewHolder, toPos: Int, x: Int, y: Int): Unit

Called when onMove(RecyclerView, ViewHolder, ViewHolder) returns true.

ItemTouchHelper does not create an extra Bitmap or View while dragging, instead, it modifies the existing View. Because of this reason, it is important that the View is still part of the layout after it is moved. This may not work as intended when swapped Views are close to RecyclerView bounds or there are gaps between them (e.g. other Views which were not eligible for dropping over).

This method is responsible to give necessary hint to the LayoutManager so that it will keep the View in visible area. For example, for LinearLayoutManager, this is as simple as calling LinearLayoutManager#scrollToPositionWithOffset(int, int). Default implementation calls RecyclerView#scrollToPosition(int) if the View's new position is likely to be out of bounds.

It is important to ensure the ViewHolder will stay visible as otherwise, it might be removed by the LayoutManager if the move causes the View to go out of bounds. In that case, drag will end prematurely.

Parameters
recyclerView	RecyclerView: The RecyclerView controlled by the ItemTouchHelper.
viewHolder	RecyclerView: The ViewHolder under user's control.
fromPos	RecyclerView: The previous adapter position of the dragged item (before it was moved).
target	RecyclerView: The ViewHolder on which the currently active item has been dropped.
toPos	RecyclerView: The new adapter position of the dragged item.
x	RecyclerView: The updated left value of the dragged View after drag translations are applied. This value does not include margins added by RecyclerView.ItemDecorations.
y	RecyclerView: The updated top value of the dragged View after drag translations are applied. This value does not include margins added by RecyclerView.ItemDecorations.

onSelectedChanged

open fun onSelectedChanged(@Nullable viewHolder: RecyclerView.ViewHolder?, actionState: Int): Unit

Called when the ViewHolder swiped or dragged by the ItemTouchHelper is changed.

If you override this method, you should call super.

Parameters
viewHolder	RecyclerView.ViewHolder?: The new ViewHolder that is being swiped or dragged. Might be null if it is cleared.
actionState	RecyclerView.ViewHolder?: One of ItemTouchHelper#ACTION_STATE_IDLE, ItemTouchHelper#ACTION_STATE_SWIPE or ItemTouchHelper#ACTION_STATE_DRAG.

See Also

• #clearView(RecyclerView, RecyclerView.ViewHolder)

onSwiped

abstract fun onSwiped(@NonNull viewHolder: RecyclerView.ViewHolder, direction: Int): Unit

Called when a ViewHolder is swiped by the user.

If you are returning relative directions (START , END) from the getMovementFlags(RecyclerView, ViewHolder) method, this method will also use relative directions. Otherwise, it will use absolute directions.

If you don't support swiping, this method will never be called.

ItemTouchHelper will keep a reference to the View until it is detached from RecyclerView. As soon as it is detached, ItemTouchHelper will call clearView(RecyclerView, ViewHolder).

Parameters
viewHolder	RecyclerView.ViewHolder: The ViewHolder which has been swiped by the user.
direction	RecyclerView.ViewHolder: The direction to which the ViewHolder is swiped. It is one of UP, DOWN, LEFT or RIGHT. If your getMovementFlags(RecyclerView, ViewHolder) method returned relative flags instead of LEFT / RIGHT; `direction` will be relative as well. (START or ).