ItemTouchHelper.Callback

public static abstract class ItemTouchHelper.Callback
extends Object

java.lang.Object
   ↳ 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. (ItemTouchHelper.LEFT, ItemTouchHelper.RIGHT, ItemTouchHelper.START, ItemTouchHelper.END, ItemTouchHelper.UP, ItemTouchHelper.DOWN). You can use makeMovementFlags(int, int) to easily construct it. Alternatively, you can use ItemTouchHelper.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

int DEFAULT_DRAG_ANIMATION_DURATION

int DEFAULT_SWIPE_ANIMATION_DURATION

Public constructors

Callback()

Public methods

boolean canDropOver(RecyclerView recyclerView, RecyclerView.ViewHolder current, RecyclerView.ViewHolder target)

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

RecyclerView.ViewHolder chooseDropTarget(RecyclerView.ViewHolder selected, List<RecyclerView.ViewHolder> dropTargets, int curX, int curY)

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

void clearView(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder)

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

int convertToAbsoluteDirection(int flags, int layoutDirection)

Converts a given set of flags to absolution direction which means ItemTouchHelper.START and ItemTouchHelper.END are replaced with ItemTouchHelper.LEFT and ItemTouchHelper.RIGHT depending on the layout direction.

static int convertToRelativeDirection(int flags, int layoutDirection)

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

long getAnimationDuration(RecyclerView recyclerView, int animationType, float animateDx, float animateDy)

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

int getBoundingBoxMargin()

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

static ItemTouchUIUtil getDefaultUIUtil()

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

float getMoveThreshold(RecyclerView.ViewHolder viewHolder)

Returns the fraction that the user should move the View to be considered as it is dragged.

abstract int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder)

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

float getSwipeEscapeVelocity(float defaultValue)

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

float getSwipeThreshold(RecyclerView.ViewHolder viewHolder)

Returns the fraction that the user should move the View to be considered as swiped.

float getSwipeVelocityThreshold(float defaultValue)

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

int interpolateOutOfBoundsScroll(RecyclerView recyclerView, int viewSize, int viewSizeOutOfBounds, int totalSize, long msSinceStartScroll)

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

boolean isItemViewSwipeEnabled()

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

boolean isLongPressDragEnabled()

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

static int makeFlag(int actionState, int directions)

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

static int makeMovementFlags(int dragFlags, int swipeFlags)

Convenience method to create movement flags.

void onChildDraw(Canvas c, RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive)

Called by ItemTouchHelper on RecyclerView's onDraw callback.

void onChildDrawOver(Canvas c, RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive)

Called by ItemTouchHelper on RecyclerView's onDraw callback.

abstract boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target)

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

void onMoved(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, int fromPos, RecyclerView.ViewHolder target, int toPos, int x, int y)

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

void onSelectedChanged(RecyclerView.ViewHolder viewHolder, int actionState)

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

abstract void onSwiped(RecyclerView.ViewHolder viewHolder, int direction)

Called when a ViewHolder is swiped by the user.

Inherited methods

Constants

DEFAULT_DRAG_ANIMATION_DURATION

public static final int DEFAULT_DRAG_ANIMATION_DURATION

Constant Value: 200 (0x000000c8)

DEFAULT_SWIPE_ANIMATION_DURATION

public static final int DEFAULT_SWIPE_ANIMATION_DURATION

Constant Value: 250 (0x000000fa)

Public constructors

Callback

public Callback ()

Public methods

canDropOver

public boolean canDropOver (RecyclerView recyclerView, 
                RecyclerView.ViewHolder current, 
                RecyclerView.ViewHolder target)

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.ViewHolder: The ViewHolder that user is dragging.

target RecyclerView.ViewHolder: The ViewHolder which is below the dragged ViewHolder.

Returns
boolean True if the dragged ViewHolder can be replaced with the target ViewHolder, false otherwise.

chooseDropTarget

public RecyclerView.ViewHolder chooseDropTarget (RecyclerView.ViewHolder selected, 
                List<RecyclerView.ViewHolder> dropTargets, 
                int curX, 
                int curY)

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 List: The list of ViewHolder that are under the dragged View and candidate as a drop.

curX int: The updated left value of the dragged View after drag translations are applied. This value does not include margins added by RecyclerView.ItemDecorations.

curY int: The updated top value of the dragged View after drag translations are applied. This value does not include margins added by RecyclerView.ItemDecorations.

Returns
RecyclerView.ViewHolder A ViewHolder to whose position the dragged ViewHolder should be moved to.

clearView

public void clearView (RecyclerView recyclerView, 
                RecyclerView.ViewHolder viewHolder)

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.ViewHolder: The View that was interacted by the user.

convertToAbsoluteDirection

public int convertToAbsoluteDirection (int flags, 
                int layoutDirection)

Converts a given set of flags to absolution direction which means ItemTouchHelper.START and ItemTouchHelper.END are replaced with ItemTouchHelper.LEFT and ItemTouchHelper.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.

Returns
int Updated flags which includes only absolute direction values.

convertToRelativeDirection

public static int convertToRelativeDirection (int flags, 
                int layoutDirection)

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).

Returns
int Updated flags which uses relative flags (ItemTouchHelper.START, ItemTouchHelper.END) instead of ItemTouchHelper.LEFT, ItemTouchHelper.RIGHT.

getAnimationDuration

public long getAnimationDuration (RecyclerView recyclerView, 
                int animationType, 
                float animateDx, 
                float animateDy)

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 ItemTouchHelper.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 int: The type of animation. Is one of ItemTouchHelper.ANIMATION_TYPE_DRAG, ItemTouchHelper.ANIMATION_TYPE_SWIPE_CANCEL or ItemTouchHelper.ANIMATION_TYPE_SWIPE_SUCCESS.

animateDx float: The horizontal distance that the animation will offset

animateDy float: The vertical distance that the animation will offset

Returns
long The duration for the animation

getBoundingBoxMargin

public int getBoundingBoxMargin ()

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.

Returns
int The extra margin to be added to the hit box of the dragged View.

getDefaultUIUtil

public static ItemTouchUIUtil getDefaultUIUtil ()

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

By default, ItemTouchHelper.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;
     }
 

Returns
ItemTouchUIUtil The ItemTouchUIUtil instance that is used by the ItemTouchHelper.Callback

getMoveThreshold

public float getMoveThreshold (RecyclerView.ViewHolder viewHolder)

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.

Returns
float A float value that denotes the fraction of the View size. Default value is .5f .

getMovementFlags

public abstract int getMovementFlags (RecyclerView recyclerView, 
                RecyclerView.ViewHolder viewHolder)

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