public abstract static class ItemTouchHelper.Callback extends Object
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.
Modifier and Type | Field and Description |
---|---|
static int |
DEFAULT_DRAG_ANIMATION_DURATION |
static int |
DEFAULT_SWIPE_ANIMATION_DURATION |
Constructor and Description |
---|
Callback() |
Modifier and Type | Method and Description |
---|---|
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. |
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 |
getMoveThreshold(RecyclerView.ViewHolder viewHolder)
Returns the fraction that the user should move the View to be considered as it is
dragged.
|
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.
|
public static final int DEFAULT_DRAG_ANIMATION_DURATION
public static final int DEFAULT_SWIPE_ANIMATION_DURATION
public static ItemTouchUIUtil getDefaultUIUtil()
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; }
ItemTouchUIUtil
instance that is used by the ItemTouchHelper.Callback
public static int convertToRelativeDirection(int flags, int layoutDirection)
flags
- The flag value that include any number of movement flags.layoutDirection
- The layout direction of the View. Can be obtained from
ViewCompat.getLayoutDirection(android.view.View)
.ItemTouchHelper.START
, ItemTouchHelper.END
) instead
of ItemTouchHelper.LEFT
, ItemTouchHelper.RIGHT
.convertToAbsoluteDirection(int, int)
public static int makeMovementFlags(int dragFlags, int swipeFlags)
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);
dragFlags
- The directions in which the item can be dragged.swipeFlags
- The directions in which the item can be swiped.public static int makeFlag(int actionState, int directions)
actionState
- The action state you want to get flags in. Should be one of
ItemTouchHelper.ACTION_STATE_IDLE
, ItemTouchHelper.ACTION_STATE_SWIPE
or
ItemTouchHelper.ACTION_STATE_DRAG
.directions
- The direction flags. Can be composed from ItemTouchHelper.UP
, ItemTouchHelper.DOWN
,
ItemTouchHelper.RIGHT
, ItemTouchHelper.LEFT
ItemTouchHelper.START
and ItemTouchHelper.END
.public abstract int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder)
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.
recyclerView
- The RecyclerView to which ItemTouchHelper is attached.viewHolder
- The ViewHolder for which the movement information is necessary.makeMovementFlags(int, int)
,
makeFlag(int, int)
public int convertToAbsoluteDirection(int flags, int layoutDirection)
ItemTouchHelper.START
and
ItemTouchHelper.END
are replaced with ItemTouchHelper.LEFT
and ItemTouchHelper.RIGHT
depending on the layout
direction.flags
- The flag value that include any number of movement flags.layoutDirection
- The layout direction of the RecyclerView.public boolean canDropOver(RecyclerView recyclerView, RecyclerView.ViewHolder current, RecyclerView.ViewHolder target)
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.
recyclerView
- The RecyclerView to which ItemTouchHelper is attached to.current
- The ViewHolder that user is dragging.target
- The ViewHolder which is below the dragged ViewHolder.public abstract boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target)
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.
recyclerView
- The RecyclerView to which ItemTouchHelper is attached to.viewHolder
- The ViewHolder which is being dragged by the user.target
- The ViewHolder over which the currently active item is being
dragged.viewHolder
has been moved to the adapter position of
target
.#onMoved(RecyclerView, ViewHolder, int, ViewHolder, int, int, int)
public boolean isLongPressDragEnabled()
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)
.
true
.#startDrag(ViewHolder)
public boolean isItemViewSwipeEnabled()
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)
.
true
.#startSwipe(ViewHolder)
public int getBoundingBoxMargin()
public float getSwipeThreshold(RecyclerView.ViewHolder viewHolder)
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.
viewHolder
- The ViewHolder that is being dragged.public float getMoveThreshold(RecyclerView.ViewHolder viewHolder)
viewHolder
- The ViewHolder that is being dragged.public float getSwipeEscapeVelocity(float defaultValue)
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.
defaultValue
- The default value (in pixels per second) used by the
ItemTouchHelper.defaultValue
parameter.getSwipeVelocityThreshold(float)
,
#getSwipeThreshold(ViewHolder)
public float getSwipeVelocityThreshold(float defaultValue)
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.
defaultValue
- The default value(in pixels per second) used by the ItemTouchHelper.defaultValue
parameter.getSwipeEscapeVelocity(float)
public RecyclerView.ViewHolder chooseDropTarget(RecyclerView.ViewHolder selected, List<RecyclerView.ViewHolder> dropTargets, int curX, int curY)
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.
selected
- The ViewHolder being dragged by the user.dropTargets
- The list of ViewHolder that are under the dragged View and
candidate as a drop.curX
- The updated left value of the dragged View after drag translations
are applied. This value does not include margins added by
RecyclerView.ItemDecoration
s.curY
- The updated top value of the dragged View after drag translations
are applied. This value does not include margins added by
RecyclerView.ItemDecoration
s.public abstract void onSwiped(RecyclerView.ViewHolder viewHolder, int direction)
If you are returning relative directions (ItemTouchHelper.START
, ItemTouchHelper.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)
.
viewHolder
- The ViewHolder which has been swiped by the user.direction
- The direction to which the ViewHolder is swiped. It is one of
ItemTouchHelper.UP
, ItemTouchHelper.DOWN
,
ItemTouchHelper.LEFT
or ItemTouchHelper.RIGHT
. If your
#getMovementFlags(RecyclerView, ViewHolder)
method
returned relative flags instead of ItemTouchHelper.LEFT
/ ItemTouchHelper.RIGHT
;
`direction` will be relative as well. (ItemTouchHelper.START
or ItemTouchHelper.END
).public void onSelectedChanged(RecyclerView.ViewHolder viewHolder, int actionState)
viewHolder
- The new ViewHolder that is being swiped or dragged. Might be null if
it is cleared.actionState
- One of ItemTouchHelper.ACTION_STATE_IDLE
,
ItemTouchHelper.ACTION_STATE_SWIPE
or
ItemTouchHelper.ACTION_STATE_DRAG
.clearView(RecyclerView, RecyclerView.ViewHolder)
public void onMoved(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, int fromPos, RecyclerView.ViewHolder target, int toPos, int x, int y)
#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.
recyclerView
- The RecyclerView controlled by the ItemTouchHelper.viewHolder
- The ViewHolder under user's control.fromPos
- The previous adapter position of the dragged item (before it was
moved).target
- The ViewHolder on which the currently active item has been dropped.toPos
- The new adapter position of the dragged item.x
- The updated left value of the dragged View after drag translations
are applied. This value does not include margins added by
RecyclerView.ItemDecoration
s.y
- The updated top value of the dragged View after drag translations
are applied. This value does not include margins added by
RecyclerView.ItemDecoration
s.public void clearView(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder)
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)
.
recyclerView
- The RecyclerView which is controlled by the ItemTouchHelper.viewHolder
- The View that was interacted by the user.public void onChildDraw(Canvas c, RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive)
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 ViewGroup.getChildDrawingOrder(int, int)
and on L
and after, it changes View's elevation value to be greater than all other children.)
c
- The canvas which RecyclerView is drawing its childrenrecyclerView
- The RecyclerView to which ItemTouchHelper is attached toviewHolder
- The ViewHolder which is being interacted by the User or it was
interacted and simply animating to its original positiondX
- The amount of horizontal displacement caused by user's actiondY
- The amount of vertical displacement caused by user's actionactionState
- The type of interaction on the View. Is either ItemTouchHelper.ACTION_STATE_DRAG
or ItemTouchHelper.ACTION_STATE_SWIPE
.isCurrentlyActive
- True if this view is currently being controlled by the user or
false it is simply animating back to its original state.#onChildDrawOver(Canvas, RecyclerView, ViewHolder, float, float, int,
boolean)
public void onChildDrawOver(Canvas c, RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive)
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 ViewGroup.getChildDrawingOrder(int, int)
and on L
and after, it changes View's elevation value to be greater than all other children.)
c
- The canvas which RecyclerView is drawing its childrenrecyclerView
- The RecyclerView to which ItemTouchHelper is attached toviewHolder
- The ViewHolder which is being interacted by the User or it was
interacted and simply animating to its original positiondX
- The amount of horizontal displacement caused by user's actiondY
- The amount of vertical displacement caused by user's actionactionState
- The type of interaction on the View. Is either ItemTouchHelper.ACTION_STATE_DRAG
or ItemTouchHelper.ACTION_STATE_SWIPE
.isCurrentlyActive
- True if this view is currently being controlled by the user or
false it is simply animating back to its original state.#onChildDrawOver(Canvas, RecyclerView, ViewHolder, float, float, int,
boolean)
public long getAnimationDuration(RecyclerView recyclerView, int animationType, float animateDx, float animateDy)
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.
recyclerView
- The RecyclerView to which the ItemTouchHelper is attached to.animationType
- The type of animation. Is one of ItemTouchHelper.ANIMATION_TYPE_DRAG
,
ItemTouchHelper.ANIMATION_TYPE_SWIPE_CANCEL
or
ItemTouchHelper.ANIMATION_TYPE_SWIPE_SUCCESS
.animateDx
- The horizontal distance that the animation will offsetanimateDy
- The vertical distance that the animation will offsetpublic int interpolateOutOfBoundsScroll(RecyclerView recyclerView, int viewSize, int viewSizeOutOfBounds, int totalSize, long msSinceStartScroll)
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.
recyclerView
- The RecyclerView instance to which ItemTouchHelper is
attached to.viewSize
- The total size of the View in scroll direction, excluding
item decorations.viewSizeOutOfBounds
- 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
- The total size of RecyclerView in the scroll direction.msSinceStartScroll
- The time passed since View is kept out of bounds.RecyclerView.scrollBy(int, int)
method.