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StaggeredGridLayoutManager

public class StaggeredGridLayoutManager
extends RecyclerView.LayoutManager implements RecyclerView.SmoothScroller.ScrollVectorProvider

java.lang.Object
   ↳ android.support.v7.widget.RecyclerView.LayoutManager
     ↳ android.support.v7.widget.StaggeredGridLayoutManager


A LayoutManager that lays out children in a staggered grid formation. It supports horizontal & vertical layout as well as an ability to layout children in reverse.

Staggered grids are likely to have gaps at the edges of the layout. To avoid these gaps, StaggeredGridLayoutManager can offset spans independently or move items between spans. You can control this behavior via setGapStrategy(int).

Summary

Nested classes

class StaggeredGridLayoutManager.LayoutParams

LayoutParams used by StaggeredGridLayoutManager. 

Inherited XML attributes

From class android.support.v7.widget.RecyclerView.LayoutManager

Constants

int GAP_HANDLING_LAZY

This constant was deprecated in API level 22.0.0. No longer supported.

int GAP_HANDLING_MOVE_ITEMS_BETWEEN_SPANS

When scroll state is changed to SCROLL_STATE_IDLE, StaggeredGrid will check if there are gaps in the because of full span items.

int GAP_HANDLING_NONE

Does not do anything to hide gaps.

int HORIZONTAL

int VERTICAL

Public constructors

StaggeredGridLayoutManager(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes)

Constructor used when layout manager is set in XML by RecyclerView attribute "layoutManager".

StaggeredGridLayoutManager(int spanCount, int orientation)

Creates a StaggeredGridLayoutManager with given parameters.

Public methods

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.

boolean checkLayoutParams(RecyclerView.LayoutParams lp)

Determines the validity of the supplied LayoutParams object.

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[] findFirstCompletelyVisibleItemPositions(int[] into)

Returns the adapter position of the first completely visible view for each span.

int[] findFirstVisibleItemPositions(int[] into)

Returns the adapter position of the first visible view for each span.

int[] findLastCompletelyVisibleItemPositions(int[] into)

Returns the adapter position of the last completely visible view for each span.

int[] findLastVisibleItemPositions(int[] into)

Returns the adapter position of the last visible view for each span.

RecyclerView.LayoutParams generateDefaultLayoutParams()

Create a default LayoutParams object for a child of the RecyclerView.

RecyclerView.LayoutParams generateLayoutParams(Context c, AttributeSet attrs)

Create a LayoutParams object suitable for this LayoutManager from an inflated layout resource.

RecyclerView.LayoutParams generateLayoutParams(ViewGroup.LayoutParams lp)

Create a LayoutParams object suitable for this LayoutManager, copying relevant values from the supplied LayoutParams object if possible.

int getColumnCountForAccessibility(RecyclerView.Recycler recycler, RecyclerView.State state)

Returns the number of columns for accessibility.

int getGapStrategy()

Returns the current gap handling strategy for StaggeredGridLayoutManager.

int getOrientation()
boolean getReverseLayout()

Returns whether views are laid out in reverse order or not.

int getRowCountForAccessibility(RecyclerView.Recycler recycler, RecyclerView.State state)

Returns the number of rows for accessibility.

int getSpanCount()

Returns the number of spans laid out by StaggeredGridLayoutManager.

void invalidateSpanAssignments()

For consistency, StaggeredGridLayoutManager keeps a mapping between spans and items.

void offsetChildrenHorizontal(int dx)

Offset all child views attached to the parent RecyclerView by dx pixels along the horizontal axis.

void offsetChildrenVertical(int dy)

Offset all child views attached to the parent RecyclerView by dy pixels along the vertical axis.

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 direction, 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 onInitializeAccessibilityNodeInfoForItem(RecyclerView.Recycler recycler, RecyclerView.State state, View host, AccessibilityNodeInfoCompat info)

Called by the AccessibilityDelegate when the accessibility information for a specific item should be populated.

void onItemsAdded(RecyclerView recyclerView, int positionStart, int itemCount)

Called when items have been added to the adapter.

void onItemsChanged(RecyclerView recyclerView)

Called when notifyDataSetChanged() is triggered instead of giving detailed information on what has actually changed.

void onItemsMoved(RecyclerView recyclerView, int from, int to, int itemCount)

Called when an item is moved withing the adapter.

void onItemsRemoved(RecyclerView recyclerView, int positionStart, int itemCount)

Called when items have been removed from the adapter.

void onItemsUpdated(RecyclerView recyclerView, int positionStart, int itemCount, Object payload)

Called when items have been changed in the adapter and with optional payload.

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 onScrollStateChanged(int state)

RecyclerView calls this method to notify LayoutManager that scroll state has changed.

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 to the specified adapter position.

void scrollToPositionWithOffset(int position, int offset)

Scroll to the specified adapter position with the given offset from 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 setGapStrategy(int gapStrategy)

Sets the gap handling strategy for StaggeredGridLayoutManager.

void setMeasuredDimension(Rect childrenBounds, int wSpec, int hSpec)

Sets the measured dimensions from the given bounding box of the children and the measurement specs that were passed into onMeasure(int, int).

void setOrientation(int orientation)

Sets the orientation of the layout.

void setReverseLayout(boolean reverseLayout)

Sets whether LayoutManager should start laying out items from the end of the UI.

void setSpanCount(int spanCount)

Sets the number of spans for the layout.

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.

Inherited methods

From class android.support.v7.widget.RecyclerView.LayoutManager
From class java.lang.Object
From interface android.support.v7.widget.RecyclerView.SmoothScroller.ScrollVectorProvider

Constants

GAP_HANDLING_LAZY

added in version 22.0.0
int GAP_HANDLING_LAZY

This constant was deprecated in API level 22.0.0.
No longer supported.

Constant Value: 1 (0x00000001)

GAP_HANDLING_MOVE_ITEMS_BETWEEN_SPANS

added in version 22.0.0
int GAP_HANDLING_MOVE_ITEMS_BETWEEN_SPANS

When scroll state is changed to SCROLL_STATE_IDLE, StaggeredGrid will check if there are gaps in the because of full span items. If it finds, it will re-layout and move items to correct positions with animations.

For example, if LayoutManager ends up with the following layout due to adapter changes:

 AAA
 _BC
 DDD
 

It will animate to the following state:

 AAA
 BC_
 DDD
 

Constant Value: 2 (0x00000002)

GAP_HANDLING_NONE

added in version 22.0.0
int GAP_HANDLING_NONE

Does not do anything to hide gaps.

Constant Value: 0 (0x00000000)

HORIZONTAL

added in version 22.0.0
int HORIZONTAL

Constant Value: 0 (0x00000000)

VERTICAL

added in version 22.0.0
int VERTICAL

Constant Value: 1 (0x00000001)

Public constructors

StaggeredGridLayoutManager

added in version 22.2.0
StaggeredGridLayoutManager (Context context, 
                AttributeSet attrs, 
                int defStyleAttr, 
                int defStyleRes)

Constructor used when layout manager is set in XML by RecyclerView attribute "layoutManager". Defaults to single column and vertical.

Parameters
context Context
attrs AttributeSet
defStyleAttr int
defStyleRes int

StaggeredGridLayoutManager

added in version 22.0.0
StaggeredGridLayoutManager (int spanCount, 
                int orientation)

Creates a StaggeredGridLayoutManager with given parameters.

Parameters
spanCount int: If orientation is vertical, spanCount is number of columns. If orientation is horizontal, spanCount is number of rows.
orientation int: VERTICAL or HORIZONTAL

Public methods

assertNotInLayoutOrScroll

added in version 22.0.0
void assertNotInLayoutOrScroll (String message)

Checks if RecyclerView is in the middle of a layout or scroll and throws an IllegalStateException if it is.

Parameters
message String: The message for the exception. Can be null.

canScrollHorizontally

added in version 22.0.0
boolean canScrollHorizontally ()

Query if horizontal scrolling is currently supported. The default implementation returns false.

Returns
boolean True if this LayoutManager can scroll the current contents horizontally

canScrollVertically

added in version 22.0.0
boolean canScrollVertically ()

Query if vertical scrolling is currently supported. The default implementation returns false.

Returns
boolean True if this LayoutManager can scroll the current contents vertically

checkLayoutParams

added in version 22.0.0
boolean checkLayoutParams (RecyclerView.LayoutParams lp)

Determines the validity of the supplied LayoutParams object.

This should check to make sure that the object is of the correct type and all values are within acceptable ranges. The default implementation returns true for non-null params.

Parameters
lp RecyclerView.LayoutParams: LayoutParams object to check
Returns
boolean true if this LayoutParams object is valid, false otherwise

computeHorizontalScrollExtent

added in version 22.0.0
int computeHorizontalScrollExtent (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read computeHorizontalScrollExtent() for details.

Default implementation returns 0.

Parameters
state RecyclerView.State: Current state of RecyclerView
Returns
int The horizontal extent of the scrollbar's thumb

computeHorizontalScrollOffset

added in version 22.0.0
int computeHorizontalScrollOffset (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read computeHorizontalScrollOffset() for details.

Default implementation returns 0.

Parameters
state RecyclerView.State: Current State of RecyclerView where you can find total item count
Returns
int The horizontal offset of the scrollbar's thumb

computeHorizontalScrollRange

added in version 22.0.0
int computeHorizontalScrollRange (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read computeHorizontalScrollRange() for details.

Default implementation returns 0.

Parameters
state RecyclerView.State: Current State of RecyclerView where you can find total item count
Returns
int The total horizontal range represented by the vertical scrollbar

computeScrollVectorForPosition

added in version 24.2.0
PointF computeScrollVectorForPosition (int targetPosition)

Should calculate the vector that points to the direction where the target position can be found.

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.

Parameters
targetPosition int: the target position to which the returned vector should point
Returns
PointF the scroll vector for a given position.

computeVerticalScrollExtent

added in version 22.0.0
int computeVerticalScrollExtent (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read computeVerticalScrollExtent() for details.

Default implementation returns 0.

Parameters
state RecyclerView.State: Current state of RecyclerView
Returns
int The vertical extent of the scrollbar's thumb

computeVerticalScrollOffset

added in version 22.0.0
int computeVerticalScrollOffset (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read computeVerticalScrollOffset() for details.

Default implementation returns 0.

Parameters
state RecyclerView.State: Current State of RecyclerView where you can find total item count
Returns
int The vertical offset of the scrollbar's thumb

computeVerticalScrollRange

added in version 22.0.0
int computeVerticalScrollRange (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read computeVerticalScrollRange() for details.

Default implementation returns 0.

Parameters
state RecyclerView.State: Current State of RecyclerView where you can find total item count
Returns
int The total vertical range represented by the vertical scrollbar

findFirstCompletelyVisibleItemPositions

added in version 22.0.0
int[] findFirstCompletelyVisibleItemPositions (int[] into)

Returns the adapter position of the first completely visible view for each span.

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.

StaggeredGridLayoutManager may pre-cache some views that are not necessarily visible. Those views are ignored in this method.

Parameters
into int: An array to put the results into. If you don't provide any, LayoutManager will create a new one.
Returns
int[] The adapter position of the first fully visible item in each span. If a span does not have any items, NO_POSITION is returned for that span.

See also:

findFirstVisibleItemPositions

added in version 22.0.0
int[] findFirstVisibleItemPositions (int[] into)

Returns the adapter position of the first visible view for each span.

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.

StaggeredGridLayoutManager may pre-cache some views that are not necessarily visible. Those views are ignored in this method.

Parameters
into int: An array to put the results into. If you don't provide any, LayoutManager will create a new one.
Returns
int[] The adapter position of the first visible item in each span. If a span does not have any items, NO_POSITION is returned for that span.

See also:

findLastCompletelyVisibleItemPositions

added in version 22.0.0
int[] findLastCompletelyVisibleItemPositions (int[] into)

Returns the adapter position of the last completely visible view for each span.

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.

StaggeredGridLayoutManager may pre-cache some views that are not necessarily visible. Those views are ignored in this method.

Parameters
into int: An array to put the results into. If you don't provide any, LayoutManager will create a new one.
Returns
int[] The adapter position of the last fully visible item in each span. If a span does not have any items, NO_POSITION is returned for that span.

See also:

findLastVisibleItemPositions

added in version 22.0.0
int[] findLastVisibleItemPositions (int[] into)

Returns the adapter position of the last visible view for each span.

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.

StaggeredGridLayoutManager may pre-cache some views that are not necessarily visible. Those views are ignored in this method.

Parameters
into int: An array to put the results into. If you don't provide any, LayoutManager will create a new one.
Returns
int[] The adapter position of the last visible item in each span. If a span does not have any items, NO_POSITION is returned for that span.

See also:

generateDefaultLayoutParams

added in version 22.0.0
RecyclerView.LayoutParams generateDefaultLayoutParams ()

Create a default 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 checkLayoutParams(LayoutParams), generateLayoutParams(android.view.ViewGroup.LayoutParams) and generateLayoutParams(android.content.Context, android.util.AttributeSet).

Returns
RecyclerView.LayoutParams A new LayoutParams for a child view

generateLayoutParams

added in version 22.0.0
RecyclerView.LayoutParams generateLayoutParams (Context c, 
                AttributeSet attrs)

Create a LayoutParams object suitable for this LayoutManager from an inflated layout resource.

Important: if you use your own custom LayoutParams type you must also override checkLayoutParams(LayoutParams), generateLayoutParams(android.view.ViewGroup.LayoutParams) and generateLayoutParams(android.content.Context, android.util.AttributeSet).

Parameters
c Context: Context for obtaining styled attributes
attrs AttributeSet: AttributeSet describing the supplied arguments
Returns
RecyclerView.LayoutParams a new LayoutParams object

generateLayoutParams

added in version 22.0.0
RecyclerView.LayoutParams generateLayoutParams (ViewGroup.LayoutParams lp)

Create a LayoutParams object suitable for this LayoutManager, copying relevant values from the supplied LayoutParams object if possible.

Important: if you use your own custom LayoutParams type you must also override checkLayoutParams(LayoutParams), generateLayoutParams(android.view.ViewGroup.LayoutParams) and generateLayoutParams(android.content.Context, android.util.AttributeSet).

Parameters
lp ViewGroup.LayoutParams: Source LayoutParams object to copy values from
Returns
RecyclerView.LayoutParams a new LayoutParams object

getColumnCountForAccessibility

added in version 22.0.0
int getColumnCountForAccessibility (RecyclerView.Recycler recycler, 
                RecyclerView.State state)

Returns the number of columns for accessibility.

Default implementation returns the number of items in the adapter if LayoutManager supports horizontal scrolling or 1 if LayoutManager does not support horizontal scrolling.

Parameters
recycler RecyclerView.Recycler: The Recycler that can be used to convert view positions into adapter positions
state RecyclerView.State: The current state of RecyclerView
Returns
int The number of rows in LayoutManager for accessibility.

getGapStrategy

added in version 22.0.0
int getGapStrategy ()

Returns the current gap handling strategy for StaggeredGridLayoutManager.

Staggered grid may have gaps in the layout due to changes in the adapter. To avoid gaps, StaggeredGridLayoutManager provides 2 options. Check GAP_HANDLING_NONE and GAP_HANDLING_MOVE_ITEMS_BETWEEN_SPANS for details.

By default, StaggeredGridLayoutManager uses GAP_HANDLING_MOVE_ITEMS_BETWEEN_SPANS.

Returns
int Current gap handling strategy.

See also:

getOrientation

added in version 22.0.0
int getOrientation ()

Returns
int

getReverseLayout

added in version 22.0.0
boolean getReverseLayout ()

Returns whether views are laid out in reverse order or not.

Not that this value is not affected by RecyclerView's layout direction.

Returns
boolean True if layout is reversed, false otherwise

See also:

getRowCountForAccessibility

added in version 22.0.0
int getRowCountForAccessibility (RecyclerView.Recycler recycler, 
                RecyclerView.State state)

Returns the number of rows for accessibility.

Default implementation returns the number of items in the adapter if LayoutManager supports vertical scrolling or 1 if LayoutManager does not support vertical scrolling.

Parameters
recycler RecyclerView.Recycler: The Recycler that can be used to convert view positions into adapter positions
state RecyclerView.State: The current state of RecyclerView
Returns
int The number of rows in LayoutManager for accessibility.

getSpanCount

added in version 22.0.0
int getSpanCount ()

Returns the number of spans laid out by StaggeredGridLayoutManager.

Returns
int Number of spans in the layout

invalidateSpanAssignments

added in version 22.0.0
void invalidateSpanAssignments ()

For consistency, StaggeredGridLayoutManager keeps a mapping between spans and items.

If you need to cancel current assignments, you can call this method which will clear all assignments and request a new layout.

offsetChildrenHorizontal

added in version 22.0.0
void offsetChildrenHorizontal (int dx)

Offset all child views attached to the parent RecyclerView by dx pixels along the horizontal axis.

Parameters
dx int: Pixels to offset by

offsetChildrenVertical

added in version 22.0.0
void offsetChildrenVertical (int dy)

Offset all child views attached to the parent RecyclerView by dy pixels along the vertical axis.

Parameters
dy int: Pixels to offset by

onDetachedFromWindow

added in version 22.0.0
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.

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 requestLayout() to ensure that it is re-laid out when RecyclerView is re-attached.

Subclass implementations should always call through to the superclass implementation.

Parameters
view RecyclerView: The RecyclerView this LayoutManager is bound to
recycler RecyclerView.Recycler: The recycler to use if you prefer to recycle your children instead of keeping them around.

onFocusSearchFailed

added in version 22.0.0
View onFocusSearchFailed (View focused, 
                int direction, 
                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.

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, if a focusable view in the given direction is found. Otherwise, if all the existing (or the newly populated views) are unfocusable, it returns the next unfocusable view to become visible on the screen. This unfocusable view is typically the first view that's either partially or fully out of RV's padded bounded area in the given direction. The default implementation returns null.

Parameters
focused View: The currently focused view
direction int: One of FOCUS_UP, FOCUS_DOWN, FOCUS_LEFT, FOCUS_RIGHT, FOCUS_BACKWARD, FOCUS_FORWARD or 0 for not applicable
recycler RecyclerView.Recycler: The recycler to use for obtaining views for currently offscreen items
state RecyclerView.State: Transient state of RecyclerView
Returns
View The chosen view to be focused if a focusable view is found, otherwise an unfocusable view to become visible onto the screen, else null.

onInitializeAccessibilityEvent

added in version 22.0.0
void onInitializeAccessibilityEvent (AccessibilityEvent event)

Parameters
event AccessibilityEvent

onInitializeAccessibilityNodeInfoForItem

added in version 22.0.0
void onInitializeAccessibilityNodeInfoForItem (RecyclerView.Recycler recycler, 
                RecyclerView.State state, 
                View host, 
                AccessibilityNodeInfoCompat info)

Called by the AccessibilityDelegate when the accessibility information for a specific item should be populated.

Default implementation adds basic positioning information about the item.

Parameters
recycler RecyclerView.Recycler: The Recycler that can be used to convert view positions into adapter positions
state RecyclerView.State: The current state of RecyclerView
host View: The child for which accessibility node info should be populated
info AccessibilityNodeInfoCompat: The info to fill out about the item

onItemsAdded

added in version 22.0.0
void onItemsAdded (RecyclerView recyclerView, 
                int positionStart, 
                int itemCount)

Called when items have been added to the adapter. The LayoutManager may choose to requestLayout if the inserted items would require refreshing the currently visible set of child views. (e.g. currently empty space would be filled by appended items, etc.)

onItemsChanged

added in version 22.0.0
void onItemsChanged (RecyclerView recyclerView)

Called when notifyDataSetChanged() is triggered instead of giving detailed information on what has actually changed.

onItemsMoved

added in version 22.0.0
void onItemsMoved (RecyclerView recyclerView, 
                int from, 
                int to, 
                int itemCount)

Called when an item is moved withing the adapter.

Note that, an item may also change position in response to another ADD/REMOVE/MOVE operation. This callback is only called if and only if notifyItemMoved(int, int) is called.

onItemsRemoved

added in version 22.0.0
void onItemsRemoved (RecyclerView recyclerView, 
                int positionStart, 
                int itemCount)

Called when items have been removed from the adapter.

onItemsUpdated

added in version 23.0.0
void onItemsUpdated (RecyclerView recyclerView, 
                int positionStart, 
                int itemCount, 
                Object payload)

Called when items have been changed in the adapter and with optional payload. Default implementation calls onItemsUpdated(RecyclerView, int, int).

onLayoutChildren

added in version 22.0.0
void onLayoutChildren (RecyclerView.Recycler recycler, 
                RecyclerView.State state)

Lay out all relevant child views from the given adapter. The LayoutManager is in charge of the behavior of item animations. By default, RecyclerView has a non-null 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 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 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 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.

Parameters
recycler RecyclerView.Recycler: Recycler to use for fetching potentially cached views for a position
state RecyclerView.State: Transient state of RecyclerView

onLayoutCompleted

added in version 24.0.0
void onLayoutCompleted (RecyclerView.State state)

Called after a full layout calculation is finished. The layout calculation may include multiple 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 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.

Parameters
state RecyclerView.State: Transient state of RecyclerView

onRestoreInstanceState

added in version 22.0.0
void onRestoreInstanceState (Parcelable state)

Parameters
state Parcelable

onSaveInstanceState

added in version 22.0.0
Parcelable onSaveInstanceState ()

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.

Returns
Parcelable Necessary information for LayoutManager to be able to restore its state

onScrollStateChanged

added in version 22.0.0
void onScrollStateChanged (int state)

RecyclerView calls this method to notify LayoutManager that scroll state has changed.

Parameters
state int: The new scroll state for RecyclerView

scrollHorizontallyBy

added in version 22.0.0
int scrollHorizontallyBy (int dx, 
                RecyclerView.Recycler recycler, 
                RecyclerView.State state)

Scroll horizontally by dx pixels in screen coordinates and return the distance traveled. The default implementation does nothing and returns 0.

Parameters
dx int: distance to scroll by in pixels. X increases as scroll position approaches the right.
recycler RecyclerView.Recycler: Recycler to use for fetching potentially cached views for a position
state RecyclerView.State: Transient state of RecyclerView
Returns
int The actual distance scrolled. The return value will be negative if dx was negative and scrolling proceeeded in that direction. Math.abs(result) may be less than dx if a boundary was reached.

scrollToPosition

added in version 22.0.0
void scrollToPosition (int position)

Scroll to the specified adapter position. Actual position of the item on the screen depends on the LayoutManager implementation.

Parameters
position int: Scroll to this adapter position.

scrollToPositionWithOffset

added in version 22.0.0
void scrollToPositionWithOffset (int position, 
                int offset)

Scroll to the specified adapter position with the given offset from layout start.

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).

Parameters
position int: Index (starting at 0) of the reference item.
offset int: The distance (in pixels) between the start edge of the item view and start edge of the RecyclerView.

See also:

scrollVerticallyBy

added in version 22.0.0
int scrollVerticallyBy (int dy, 
                RecyclerView.Recycler recycler, 
                RecyclerView.State state)

Scroll vertically by dy pixels in screen coordinates and return the distance traveled. The default implementation does nothing and returns 0.

Parameters
dy int: distance to scroll in pixels. Y increases as scroll position approaches the bottom.
recycler RecyclerView.Recycler: Recycler to use for fetching potentially cached views for a position
state RecyclerView.State: Transient state of RecyclerView
Returns
int The actual distance scrolled. The return value will be negative if dy was negative and scrolling proceeeded in that direction. Math.abs(result) may be less than dy if a boundary was reached.

setGapStrategy

added in version 22.0.0
void setGapStrategy (int gapStrategy)

Sets the gap handling strategy for StaggeredGridLayoutManager. If the gapStrategy parameter is different than the current strategy, calling this method will trigger a layout request.

Parameters
gapStrategy int: The new gap handling strategy. Should be GAP_HANDLING_MOVE_ITEMS_BETWEEN_SPANS or GAP_HANDLING_NONE.

See also:

setMeasuredDimension

added in version 23.2.0
void setMeasuredDimension (Rect childrenBounds, 
                int wSpec, 
                int hSpec)

Sets the measured dimensions from the given bounding box of the children and the measurement specs that were passed into onMeasure(int, int). It is called after the RecyclerView calls onLayoutChildren(Recycler, State) during a measurement pass.

This method should call setMeasuredDimension(int, int).

The default implementation adds the RecyclerView's padding to the given bounding box then caps the value to be within the given measurement specs.

This method is only called if the LayoutManager opted into the auto measurement API.

Parameters
childrenBounds Rect: The bounding box of all children
wSpec int: The widthMeasureSpec that was passed into the RecyclerView.
hSpec int: The heightMeasureSpec that was passed into the RecyclerView.

setOrientation

added in version 22.0.0
void setOrientation (int orientation)

Sets the orientation of the layout. StaggeredGridLayoutManager will do its best to keep scroll position if this method is called after views are laid out.

Parameters
orientation int: HORIZONTAL or VERTICAL

setReverseLayout

added in version 22.0.0
void setReverseLayout (boolean reverseLayout)

Sets whether LayoutManager should start laying out items from the end of the UI. The order items are traversed is not affected by this call.

For vertical layout, if it is set to true, first item will be at the bottom of the list.

For horizontal layouts, it depends on the layout direction. When set to true, If RecyclerView is LTR, than it will layout from RTL, if RecyclerView} is RTL, it will layout from LTR.

Parameters
reverseLayout boolean: Whether layout should be in reverse or not

setSpanCount

added in version 22.0.0
void setSpanCount (int spanCount)

Sets the number of spans for the layout. This will invalidate all of the span assignments for Views.

Calling this method will automatically result in a new layout request unless the spanCount parameter is equal to current span count.

Parameters
spanCount int: Number of spans to layout

smoothScrollToPosition

added in version 22.0.0
void smoothScrollToPosition (RecyclerView recyclerView, 
                RecyclerView.State state, 
                int position)

Smooth scroll to the specified adapter position.

To support smooth scrolling, override this method, create your RecyclerView.SmoothScroller instance and call startSmoothScroll(SmoothScroller).

Parameters
recyclerView RecyclerView: The RecyclerView to which this layout manager is attached
state RecyclerView.State: Current State of RecyclerView
position int: Scroll to this adapter position.

supportsPredictiveItemAnimations

added in version 22.0.0
boolean supportsPredictiveItemAnimations ()

Returns whether this LayoutManager supports automatic item animations. A LayoutManager wishing to support item animations should obey certain rules as outlined in 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.

Returns
boolean true if predictive item animations should be enabled, false otherwise
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