public class LinearLayoutManager extends RecyclerView.LayoutManager implements ItemTouchHelper.ViewDropHandler, RecyclerView.SmoothScroller.ScrollVectorProvider
RecyclerView.LayoutManager
implementation which provides
similar functionality to ListView
.Modifier and Type | Class and Description |
---|---|
protected static class |
LinearLayoutManager.LayoutChunkResult |
static class |
LinearLayoutManager.SavedState |
RecyclerView.LayoutManager.Properties
Modifier and Type | Field and Description |
---|---|
static int |
HORIZONTAL |
static int |
INVALID_OFFSET |
static int |
VERTICAL |
Constructor and Description |
---|
LinearLayoutManager(Context context)
Creates a vertical LinearLayoutManager
|
LinearLayoutManager(Context context,
AttributeSet attrs,
int defStyleAttr,
int defStyleRes)
Constructor used when layout manager is set in XML by RecyclerView attribute
"layoutManager".
|
LinearLayoutManager(Context context,
int orientation,
boolean reverseLayout) |
Modifier and Type | Method and Description |
---|---|
void |
assertNotInLayoutOrScroll(String message)
Checks if RecyclerView is in the middle of a layout or scroll and throws an
IllegalStateException if it is. |
boolean |
canScrollHorizontally()
Query if horizontal scrolling is currently supported.
|
boolean |
canScrollVertically()
Query if vertical scrolling is currently supported.
|
int |
computeHorizontalScrollExtent(RecyclerView.State state)
Override this method if you want to support scroll bars.
|
int |
computeHorizontalScrollOffset(RecyclerView.State state)
Override this method if you want to support scroll bars.
|
int |
computeHorizontalScrollRange(RecyclerView.State state)
Override this method if you want to support scroll bars.
|
PointF |
computeScrollVectorForPosition(int targetPosition)
Should calculate the vector that points to the direction where the target position
can be found.
|
int |
computeVerticalScrollExtent(RecyclerView.State state)
Override this method if you want to support scroll bars.
|
int |
computeVerticalScrollOffset(RecyclerView.State state)
Override this method if you want to support scroll bars.
|
int |
computeVerticalScrollRange(RecyclerView.State state)
Override this method if you want to support scroll bars.
|
int |
findFirstCompletelyVisibleItemPosition()
Returns the adapter position of the first fully visible view.
|
int |
findFirstVisibleItemPosition()
Returns the adapter position of the first visible view.
|
int |
findLastCompletelyVisibleItemPosition()
Returns the adapter position of the last fully visible view.
|
int |
findLastVisibleItemPosition()
Returns the adapter position of the last visible view.
|
View |
findViewByPosition(int position)
Finds the view which represents the given adapter position.
|
RecyclerView.LayoutParams |
generateDefaultLayoutParams()
Create a default
LayoutParams object for a child of the RecyclerView. |
protected int |
getExtraLayoutSpace(RecyclerView.State state)
Returns the amount of extra space that should be laid out by LayoutManager.
|
int |
getOrientation()
Returns the current orientation of the layout.
|
boolean |
getRecycleChildrenOnDetach()
Returns whether LayoutManager will recycle its children when it is detached from
RecyclerView.
|
boolean |
getReverseLayout()
Returns if views are laid out from the opposite direction of the layout.
|
boolean |
getStackFromEnd() |
protected boolean |
isLayoutRTL() |
boolean |
isSmoothScrollbarEnabled()
Returns the current state of the smooth scrollbar feature.
|
void |
onDetachedFromWindow(RecyclerView view,
RecyclerView.Recycler recycler)
Called when this LayoutManager is detached from its parent RecyclerView or when
its parent RecyclerView is detached from its window.
|
View |
onFocusSearchFailed(View focused,
int focusDirection,
RecyclerView.Recycler recycler,
RecyclerView.State state)
Called when searching for a focusable view in the given direction has failed
for the current content of the RecyclerView.
|
void |
onInitializeAccessibilityEvent(AccessibilityEvent event) |
void |
onLayoutChildren(RecyclerView.Recycler recycler,
RecyclerView.State state)
Lay out all relevant child views from the given adapter.
|
void |
onLayoutCompleted(RecyclerView.State state)
Called after a full layout calculation is finished.
|
void |
onRestoreInstanceState(Parcelable state) |
Parcelable |
onSaveInstanceState()
Called when the LayoutManager should save its state.
|
void |
prepareForDrop(View view,
View target,
int x,
int y)
Called by the
ItemTouchHelper after a View is dropped over another View. |
int |
scrollHorizontallyBy(int dx,
RecyclerView.Recycler recycler,
RecyclerView.State state)
Scroll horizontally by dx pixels in screen coordinates and return the distance traveled.
|
void |
scrollToPosition(int position)
Scroll the RecyclerView to make the position visible.
|
void |
scrollToPositionWithOffset(int position,
int offset)
Scroll to the specified adapter position with the given offset from resolved layout
start.
|
int |
scrollVerticallyBy(int dy,
RecyclerView.Recycler recycler,
RecyclerView.State state)
Scroll vertically by dy pixels in screen coordinates and return the distance traveled.
|
void |
setOrientation(int orientation)
Sets the orientation of the layout.
|
void |
setRecycleChildrenOnDetach(boolean recycleChildrenOnDetach)
Set whether LayoutManager will recycle its children when it is detached from
RecyclerView.
|
void |
setReverseLayout(boolean reverseLayout)
Used to reverse item traversal and layout order.
|
void |
setSmoothScrollbarEnabled(boolean enabled)
When smooth scrollbar is enabled, the position and size of the scrollbar thumb is computed
based on the number of visible pixels in the visible items.
|
void |
setStackFromEnd(boolean stackFromEnd)
Compatibility support for
AbsListView.setStackFromBottom(boolean) |
void |
smoothScrollToPosition(RecyclerView recyclerView,
RecyclerView.State state,
int position)
Smooth scroll to the specified adapter position.
|
boolean |
supportsPredictiveItemAnimations()
Returns whether this LayoutManager supports automatic item animations.
|
addDisappearingView, addDisappearingView, addView, addView, assertInLayoutOrScroll, attachView, attachView, attachView, calculateItemDecorationsForChild, checkLayoutParams, chooseSize, detachAndScrapAttachedViews, detachAndScrapView, detachAndScrapViewAt, detachView, detachViewAt, endAnimation, findContainingItemView, generateLayoutParams, generateLayoutParams, getBaseline, getBottomDecorationHeight, getChildAt, getChildCount, getChildMeasureSpec, getChildMeasureSpec, getClipToPadding, getColumnCountForAccessibility, getDecoratedBottom, getDecoratedBoundsWithMargins, getDecoratedLeft, getDecoratedMeasuredHeight, getDecoratedMeasuredWidth, getDecoratedRight, getDecoratedTop, getFocusedChild, getHeight, getHeightMode, getItemCount, getItemViewType, getLayoutDirection, getLeftDecorationWidth, getMinimumHeight, getMinimumWidth, getPaddingBottom, getPaddingEnd, getPaddingLeft, getPaddingRight, getPaddingStart, getPaddingTop, getPosition, getProperties, getRightDecorationWidth, getRowCountForAccessibility, getSelectionModeForAccessibility, getTopDecorationHeight, getTransformedBoundingBox, getWidth, getWidthMode, hasFocus, ignoreView, isAttachedToWindow, isAutoMeasureEnabled, isFocused, isItemPrefetchEnabled, isLayoutHierarchical, isMeasurementCacheEnabled, isSmoothScrolling, layoutDecorated, layoutDecoratedWithMargins, measureChild, measureChildWithMargins, moveView, offsetChildrenHorizontal, offsetChildrenVertical, onAdapterChanged, onAddFocusables, onAttachedToWindow, onDetachedFromWindow, onInitializeAccessibilityEvent, onInitializeAccessibilityNodeInfo, onInitializeAccessibilityNodeInfoForItem, onInterceptFocusSearch, onItemsAdded, onItemsChanged, onItemsMoved, onItemsRemoved, onItemsUpdated, onItemsUpdated, onMeasure, onRequestChildFocus, onRequestChildFocus, onScrollStateChanged, performAccessibilityAction, performAccessibilityActionForItem, postOnAnimation, removeAllViews, removeAndRecycleAllViews, removeAndRecycleView, removeAndRecycleViewAt, removeCallbacks, removeDetachedView, removeView, removeViewAt, requestChildRectangleOnScreen, requestLayout, requestSimpleAnimationsInNextLayout, setAutoMeasureEnabled, setItemPrefetchEnabled, setMeasuredDimension, setMeasuredDimension, setMeasurementCacheEnabled, startSmoothScroll, stopIgnoringView
public static final int HORIZONTAL
public static final int VERTICAL
public static final int INVALID_OFFSET
public LinearLayoutManager(Context context)
context
- Current context, will be used to access resources.public LinearLayoutManager(Context context, int orientation, boolean reverseLayout)
context
- Current context, will be used to access resources.orientation
- Layout orientation. Should be HORIZONTAL
or VERTICAL
.reverseLayout
- When set to true, layouts from end to start.public LinearLayoutManager(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes)
public RecyclerView.LayoutParams generateDefaultLayoutParams()
LayoutParams
object for a child of the RecyclerView.
LayoutManagers will often want to use a custom LayoutParams
type
to store extra information specific to the layout. Client code should subclass
RecyclerView.LayoutParams
for this purpose.
Important: if you use your own custom LayoutParams
type
you must also override
ViewGroup.checkLayoutParams(LayoutParams)
,
RecyclerView.LayoutManager.generateLayoutParams(android.view.ViewGroup.LayoutParams)
and
RecyclerView.LayoutManager.generateLayoutParams(android.content.Context, android.util.AttributeSet)
.
generateDefaultLayoutParams
in class RecyclerView.LayoutManager
public boolean getRecycleChildrenOnDetach()
public void setRecycleChildrenOnDetach(boolean recycleChildrenOnDetach)
If you are using a RecyclerView.RecycledViewPool
, it might be a good idea to set
this flag to true
so that views will be available to other RecyclerViews
immediately.
Note that, setting this flag will result in a performance drop if RecyclerView is restored.
recycleChildrenOnDetach
- Whether children should be recycled in detach or not.public void onDetachedFromWindow(RecyclerView view, RecyclerView.Recycler recycler)
RecyclerView.LayoutManager
LayoutManager should clear all of its View references as another LayoutManager might be assigned to the RecyclerView.
If the RecyclerView is re-attached with the same LayoutManager and Adapter, it may not
call #onLayoutChildren(Recycler, State)
if nothing has changed and a layout was
not requested on the RecyclerView while it was detached.
If your LayoutManager has View references that it cleans in on-detach, it should also
call RecyclerView.requestLayout()
to ensure that it is re-laid out when
RecyclerView is re-attached.
Subclass implementations should always call through to the superclass implementation.
onDetachedFromWindow
in class RecyclerView.LayoutManager
view
- The RecyclerView this LayoutManager is bound torecycler
- The recycler to use if you prefer to recycle your children instead of
keeping them around.RecyclerView.LayoutManager.onAttachedToWindow(RecyclerView)
public void onInitializeAccessibilityEvent(AccessibilityEvent event)
onInitializeAccessibilityEvent
in class RecyclerView.LayoutManager
public Parcelable onSaveInstanceState()
RecyclerView.LayoutManager
Called when the LayoutManager should save its state. This is a good time to save your scroll position, configuration and anything else that may be required to restore the same layout state if the LayoutManager is recreated.
RecyclerView does NOT verify if the LayoutManager has changed between state save and restore. This will let you share information between your LayoutManagers but it is also your responsibility to make sure they use the same parcelable class.
onSaveInstanceState
in class RecyclerView.LayoutManager
public void onRestoreInstanceState(Parcelable state)
onRestoreInstanceState
in class RecyclerView.LayoutManager
public boolean canScrollHorizontally()
RecyclerView.LayoutManager
canScrollHorizontally
in class RecyclerView.LayoutManager
getOrientation()
is HORIZONTAL
public boolean canScrollVertically()
RecyclerView.LayoutManager
canScrollVertically
in class RecyclerView.LayoutManager
getOrientation()
is VERTICAL
public void setStackFromEnd(boolean stackFromEnd)
AbsListView.setStackFromBottom(boolean)
public boolean getStackFromEnd()
public int getOrientation()
HORIZONTAL
or VERTICAL
setOrientation(int)
public void setOrientation(int orientation)
LinearLayoutManager
will do its best to keep scroll position.orientation
- HORIZONTAL
or VERTICAL
public boolean getReverseLayout()
setReverseLayout(boolean)
public void setReverseLayout(boolean reverseLayout)
RecyclerView
is LTR, than it will
layout from RTL, if RecyclerView
} is RTL, it will layout
from LTR.
If you are looking for the exact same behavior of
AbsListView.setStackFromBottom(boolean)
, use
setStackFromEnd(boolean)
public View findViewByPosition(int position)
This method traverses each child since it has no information about child order. Override this method to improve performance if your LayoutManager keeps data about child views.
If a view is ignored via RecyclerView.LayoutManager.ignoreView(View)
, it is also ignored by this method.
findViewByPosition
in class RecyclerView.LayoutManager
position
- Position of the item in adapterprotected int getExtraLayoutSpace(RecyclerView.State state)
Returns the amount of extra space that should be laid out by LayoutManager.
By default, LinearLayoutManager
lays out 1 extra page of
items while smooth scrolling and 0 otherwise. You can override this method to implement your
custom layout pre-cache logic.
Laying out invisible elements will eventually come with performance cost. On the other hand, in places like smooth scrolling to an unknown location, this extra content helps LayoutManager to calculate a much smoother scrolling; which improves user experience.
You can also use this if you are trying to pre-layout your upcoming views.
public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state, int position)
RecyclerView.LayoutManager
Smooth scroll to the specified adapter position.
To support smooth scrolling, override this method, create your RecyclerView.SmoothScroller
instance and call #startSmoothScroll(SmoothScroller)
.
smoothScrollToPosition
in class RecyclerView.LayoutManager
recyclerView
- The RecyclerView to which this layout manager is attachedstate
- Current State of RecyclerViewposition
- Scroll to this adapter position.public PointF computeScrollVectorForPosition(int targetPosition)
RecyclerView.SmoothScroller.ScrollVectorProvider
This method is used by the LinearSmoothScroller
to initiate a scroll towards
the target position.
The magnitude of the vector is not important. It is always normalized before being
used by the LinearSmoothScroller
.
LayoutManager should not check whether the position exists in the adapter or not.
computeScrollVectorForPosition
in interface RecyclerView.SmoothScroller.ScrollVectorProvider
targetPosition
- the target position to which the returned vector should pointpublic void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state)
ItemAnimator
, and simple
item animations are enabled. This means that add/remove operations on the
adapter will result in animations to add new or appearing items, removed or
disappearing items, and moved items. If a LayoutManager returns false from
RecyclerView.LayoutManager.supportsPredictiveItemAnimations()
, which is the default, and runs a
normal layout operation during #onLayoutChildren(Recycler, State)
, the
RecyclerView will have enough information to run those animations in a simple
way. For example, the default ItemAnimator, DefaultItemAnimator
, will
simply fade views in and out, whether they are actually added/removed or whether
they are moved on or off the screen due to other add/remove operations.
A LayoutManager wanting a better item animation experience, where items can be
animated onto and off of the screen according to where the items exist when they
are not on screen, then the LayoutManager should return true from
RecyclerView.LayoutManager.supportsPredictiveItemAnimations()
and add additional logic to
#onLayoutChildren(Recycler, State)
. Supporting predictive animations
means that #onLayoutChildren(Recycler, State)
will be called twice;
once as a "pre" layout step to determine where items would have been prior to
a real layout, and again to do the "real" layout. In the pre-layout phase,
items will remember their pre-layout positions to allow them to be laid out
appropriately. Also, removed
items will
be returned from the scrap to help determine correct placement of other items.
These removed items should not be added to the child list, but should be used
to help calculate correct positioning of other views, including views that
were not previously onscreen (referred to as APPEARING views), but whose
pre-layout offscreen position can be determined given the extra
information about the pre-layout removed views.
The second layout pass is the real layout in which only non-removed views
will be used. The only additional requirement during this pass is, if
RecyclerView.LayoutManager.supportsPredictiveItemAnimations()
returns true, to note which
views exist in the child list prior to layout and which are not there after
layout (referred to as DISAPPEARING views), and to position/layout those views
appropriately, without regard to the actual bounds of the RecyclerView. This allows
the animation system to know the location to which to animate these disappearing
views.
The default LayoutManager implementations for RecyclerView handle all of these requirements for animations already. Clients of RecyclerView can either use one of these layout managers directly or look at their implementations of onLayoutChildren() to see how they account for the APPEARING and DISAPPEARING views.
onLayoutChildren
in class RecyclerView.LayoutManager
recycler
- Recycler to use for fetching potentially cached views for a
positionstate
- Transient state of RecyclerViewpublic void onLayoutCompleted(RecyclerView.State state)
RecyclerView.LayoutManager
#onLayoutChildren(Recycler, State)
calls due to animations or
layout measurement but it will include only one #onLayoutCompleted(State)
call.
This method will be called at the end of View.layout(int, int, int, int)
call.
This is a good place for the LayoutManager to do some cleanup like pending scroll position, saved state etc.
onLayoutCompleted
in class RecyclerView.LayoutManager
state
- Transient state of RecyclerViewprotected boolean isLayoutRTL()
public void scrollToPosition(int position)
Scroll the RecyclerView to make the position visible.
RecyclerView will scroll the minimum amount that is necessary to make the
target position visible. If you are looking for a similar behavior to
ListView.setSelection(int)
or
AbsListView.setSelectionFromTop(int, int)
, use
scrollToPositionWithOffset(int, int)
.
Note that scroll position change will not be reflected until the next layout call.
scrollToPosition
in class RecyclerView.LayoutManager
position
- Scroll to this adapter positionscrollToPositionWithOffset(int, int)
public void scrollToPositionWithOffset(int position, int offset)
getReverseLayout()
,
ViewCompat.getLayoutDirection(android.view.View)
and getStackFromEnd()
.
For example, if layout is VERTICAL
and getStackFromEnd()
is true, calling
scrollToPositionWithOffset(10, 20)
will layout such that
item[10]
's bottom is 20 pixels above the RecyclerView's bottom.
Note that scroll position change will not be reflected until the next layout call.
If you are just trying to make a position visible, use scrollToPosition(int)
.
position
- Index (starting at 0) of the reference item.offset
- The distance (in pixels) between the start edge of the item view and
start edge of the RecyclerView.setReverseLayout(boolean)
,
scrollToPosition(int)
public int scrollHorizontallyBy(int dx, RecyclerView.Recycler recycler, RecyclerView.State state)
scrollHorizontallyBy
in class RecyclerView.LayoutManager
dx
- distance to scroll by in pixels. X increases as scroll position
approaches the right.recycler
- Recycler to use for fetching potentially cached views for a
positionstate
- Transient state of RecyclerViewMath.abs(result)
may be less than dx if a boundary was reached.public int scrollVerticallyBy(int dy, RecyclerView.Recycler recycler, RecyclerView.State state)
scrollVerticallyBy
in class RecyclerView.LayoutManager
dy
- distance to scroll in pixels. Y increases as scroll position
approaches the bottom.recycler
- Recycler to use for fetching potentially cached views for a
positionstate
- Transient state of RecyclerViewMath.abs(result)
may be less than dy if a boundary was reached.public int computeHorizontalScrollOffset(RecyclerView.State state)
RecyclerView.LayoutManager
Override this method if you want to support scroll bars.
Read RecyclerView.computeHorizontalScrollOffset()
for details.
Default implementation returns 0.
computeHorizontalScrollOffset
in class RecyclerView.LayoutManager
state
- Current State of RecyclerView where you can find total item countRecyclerView.computeHorizontalScrollOffset()
public int computeVerticalScrollOffset(RecyclerView.State state)
RecyclerView.LayoutManager
Override this method if you want to support scroll bars.
Read RecyclerView.computeVerticalScrollOffset()
for details.
Default implementation returns 0.
computeVerticalScrollOffset
in class RecyclerView.LayoutManager
state
- Current State of RecyclerView where you can find total item countRecyclerView.computeVerticalScrollOffset()
public int computeHorizontalScrollExtent(RecyclerView.State state)
RecyclerView.LayoutManager
Override this method if you want to support scroll bars.
Read RecyclerView.computeHorizontalScrollExtent()
for details.
Default implementation returns 0.
computeHorizontalScrollExtent
in class RecyclerView.LayoutManager
state
- Current state of RecyclerViewRecyclerView.computeHorizontalScrollExtent()
public int computeVerticalScrollExtent(RecyclerView.State state)
RecyclerView.LayoutManager
Override this method if you want to support scroll bars.
Read RecyclerView.computeVerticalScrollExtent()
for details.
Default implementation returns 0.
computeVerticalScrollExtent
in class RecyclerView.LayoutManager
state
- Current state of RecyclerViewRecyclerView.computeVerticalScrollExtent()
public int computeHorizontalScrollRange(RecyclerView.State state)
RecyclerView.LayoutManager
Override this method if you want to support scroll bars.
Read RecyclerView.computeHorizontalScrollRange()
for details.
Default implementation returns 0.
computeHorizontalScrollRange
in class RecyclerView.LayoutManager
state
- Current State of RecyclerView where you can find total item countRecyclerView.computeHorizontalScrollRange()
public int computeVerticalScrollRange(RecyclerView.State state)
RecyclerView.LayoutManager
Override this method if you want to support scroll bars.
Read RecyclerView.computeVerticalScrollRange()
for details.
Default implementation returns 0.
computeVerticalScrollRange
in class RecyclerView.LayoutManager
state
- Current State of RecyclerView where you can find total item countRecyclerView.computeVerticalScrollRange()
public void setSmoothScrollbarEnabled(boolean enabled)
enabled
- Whether or not to enable smooth scrollbar.setSmoothScrollbarEnabled(boolean)
public boolean isSmoothScrollbarEnabled()
setSmoothScrollbarEnabled(boolean)
public void assertNotInLayoutOrScroll(String message)
RecyclerView.LayoutManager
IllegalStateException
if it is.assertNotInLayoutOrScroll
in class RecyclerView.LayoutManager
message
- The message for the exception. Can be null.RecyclerView.LayoutManager.assertInLayoutOrScroll(String)
public int findFirstVisibleItemPosition()
Note that, this value is not affected by layout orientation or item order traversal.
(setReverseLayout(boolean)
). Views are sorted by their positions in the adapter,
not in the layout.
If RecyclerView has item decorators, they will be considered in calculations as well.
LayoutManager may pre-cache some views that are not necessarily visible. Those views are ignored in this method.
RecyclerView.NO_POSITION
if
there aren't any visible items.findFirstCompletelyVisibleItemPosition()
,
findLastVisibleItemPosition()
public int findFirstCompletelyVisibleItemPosition()
Note that bounds check is only performed in the current orientation. That means, if LayoutManager is horizontal, it will only check the view's left and right edges.
RecyclerView.NO_POSITION
if there aren't any visible items.findFirstVisibleItemPosition()
,
findLastCompletelyVisibleItemPosition()
public int findLastVisibleItemPosition()
Note that, this value is not affected by layout orientation or item order traversal.
(setReverseLayout(boolean)
). Views are sorted by their positions in the adapter,
not in the layout.
If RecyclerView has item decorators, they will be considered in calculations as well.
LayoutManager may pre-cache some views that are not necessarily visible. Those views are ignored in this method.
RecyclerView.NO_POSITION
if
there aren't any visible items.findLastCompletelyVisibleItemPosition()
,
findFirstVisibleItemPosition()
public int findLastCompletelyVisibleItemPosition()
Note that bounds check is only performed in the current orientation. That means, if LayoutManager is horizontal, it will only check the view's left and right edges.
RecyclerView.NO_POSITION
if there aren't any visible items.findLastVisibleItemPosition()
,
findFirstCompletelyVisibleItemPosition()
public View onFocusSearchFailed(View focused, int focusDirection, RecyclerView.Recycler recycler, RecyclerView.State state)
RecyclerView.LayoutManager
This is the LayoutManager's opportunity to populate views in the given direction to fulfill the request if it can. The LayoutManager should attach and return the view to be focused. The default implementation returns null.
onFocusSearchFailed
in class RecyclerView.LayoutManager
focused
- The currently focused viewfocusDirection
- One of View.FOCUS_UP
, View.FOCUS_DOWN
,
View.FOCUS_LEFT
, View.FOCUS_RIGHT
,
View.FOCUS_BACKWARD
, View.FOCUS_FORWARD
or 0 for not applicablerecycler
- The recycler to use for obtaining views for currently offscreen itemsstate
- Transient state of RecyclerViewpublic boolean supportsPredictiveItemAnimations()
RecyclerView.LayoutManager
#onLayoutChildren(Recycler, State)
.
The default return value is false
, so subclasses of LayoutManager
will not get predictive item animations by default.
Whether item animations are enabled in a RecyclerView is determined both
by the return value from this method and the
ItemAnimator
set on the
RecyclerView itself. If the RecyclerView has a non-null ItemAnimator but this
method returns false, then simple item animations will be enabled, in which
views that are moving onto or off of the screen are simply faded in/out. If
the RecyclerView has a non-null ItemAnimator and this method returns true,
then there will be two calls to #onLayoutChildren(Recycler, State)
to
setup up the information needed to more intelligently predict where appearing
and disappearing views should be animated from/to.
supportsPredictiveItemAnimations
in class RecyclerView.LayoutManager
public void prepareForDrop(View view, View target, int x, int y)
ItemTouchHelper.ViewDropHandler
ItemTouchHelper
after a View is dropped over another View.
A LayoutManager should implement this interface to get ready for the upcoming move operation.
For example, LinearLayoutManager sets up a "scrollToPositionWithOffset" calls so that the View under drag will be used as an anchor View while calculating the next layout, making layout stay consistent.
prepareForDrop
in interface ItemTouchHelper.ViewDropHandler
view
- The View which is being dragged. It is very likely that user is still
dragging this View so there might be other
ItemTouchHelper.ViewDropHandler.prepareForDrop(View, View, int, int)
after this one.target
- The target view which is being dropped on.x
- The left
offset of the View that is being dragged. This value
includes the movement caused by the user.y
- The top
offset of the View that is being dragged. This value
includes the movement caused by the user.