StaggeredGridLayoutManager

GAP_HANDLING_LAZY

int GAP_HANDLING_LAZY

This constant was deprecated in API level 22.1.0.
No longer supported.

Constant Value: 1 (0x00000001)

GAP_HANDLING_MOVE_ITEMS_BETWEEN_SPANS

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

int GAP_HANDLING_NONE

Does not do anything to hide gaps.

Constant Value: 0 (0x00000000)

HORIZONTAL

int HORIZONTAL

Constant Value: 0 (0x00000000)

VERTICAL

int VERTICAL

Constant Value: 1 (0x00000001)

StaggeredGridLayoutManager

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.

StaggeredGridLayoutManager

StaggeredGridLayoutManager (int spanCount, 
                int orientation)

Creates a StaggeredGridLayoutManager with given parameters.

assertNotInLayoutOrScroll

void assertNotInLayoutOrScroll (String message)

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

canScrollHorizontally

boolean canScrollHorizontally ()

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

canScrollVertically

boolean canScrollVertically ()

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

checkLayoutParams

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.

computeHorizontalScrollExtent

int computeHorizontalScrollExtent (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read computeHorizontalScrollExtent() for details.

Default implementation returns 0.

computeHorizontalScrollOffset

int computeHorizontalScrollOffset (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read computeHorizontalScrollOffset() for details.

Default implementation returns 0.

computeHorizontalScrollRange

int computeHorizontalScrollRange (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read computeHorizontalScrollRange() for details.

Default implementation returns 0.

computeScrollVectorForPosition

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.

computeVerticalScrollExtent

int computeVerticalScrollExtent (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read computeVerticalScrollExtent() for details.

Default implementation returns 0.

computeVerticalScrollOffset

int computeVerticalScrollOffset (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read computeVerticalScrollOffset() for details.

Default implementation returns 0.

computeVerticalScrollRange

int computeVerticalScrollRange (RecyclerView.State state)

Override this method if you want to support scroll bars.

Read computeVerticalScrollRange() for details.

Default implementation returns 0.

findFirstCompletelyVisibleItemPositions

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.

findFirstVisibleItemPositions

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.

findLastCompletelyVisibleItemPositions

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.

findLastVisibleItemPositions

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.

generateDefaultLayoutParams

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).

generateLayoutParams

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).

generateLayoutParams

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).

getColumnCountForAccessibility

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.

getGapStrategy

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.

getOrientation

int getOrientation ()

getReverseLayout

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.

getRowCountForAccessibility

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.

getSpanCount

int getSpanCount ()

Returns the number of spans laid out by StaggeredGridLayoutManager.

invalidateSpanAssignments

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.

isAutoMeasureEnabled

boolean isAutoMeasureEnabled ()

Returns whether the measuring pass of layout should use the AutoMeasure mechanism of RecyclerView or if it should be done by the LayoutManager's implementation of onMeasure(Recycler, State, int, int).

This method returns false by default (it actually returns the value passed to the deprecated setAutoMeasureEnabled(boolean)) and should be overridden to return true if a LayoutManager wants to be auto measured by the RecyclerView.

If this method is overridden to return true, onMeasure(Recycler, State, int, int) should not be overridden.

AutoMeasure is a RecyclerView mechanism that handles the measuring pass of layout in a simple and contract satisfying way, including the wrapping of children laid out by LayoutManager. Simply put, it handles wrapping children by calling onLayoutChildren(Recycler, State) during a call to onMeasure(int, int), and then calculating desired dimensions based on children's dimensions and positions. It does this while supporting all existing animation capabilities of the RecyclerView.

More specifically:

1. When onMeasure(int, int) is called, if the provided measure specs both have a mode of EXACTLY, RecyclerView will set its measured dimensions accordingly and return, allowing layout to continue as normal (Actually, RecyclerView will call onMeasure(Recycler, State, int, int) for backwards compatibility reasons but it should not be overridden if AutoMeasure is being used).
2. If one of the layout specs is not EXACT, the RecyclerView will start the layout process. It will first process all pending Adapter updates and then decide whether to run a predictive layout. If it decides to do so, it will first call onLayoutChildren(Recycler, State) with isPreLayout() set to true. At this stage, getWidth() and getHeight() will still return the width and height of the RecyclerView as of the last layout calculation.

   After handling the predictive case, RecyclerView will call onLayoutChildren(Recycler, State) with isMeasuring() set to true and isPreLayout() set to false. The LayoutManager can access the measurement specs via getHeight(), getHeightMode(), getWidth() and getWidthMode().

3. After the layout calculation, RecyclerView sets the measured width & height by calculating the bounding box for the children (+ RecyclerView's padding). The LayoutManagers can override setMeasuredDimension(Rect, int, int) to choose different values. For instance, GridLayoutManager overrides this value to handle the case where if it is vertical and has 3 columns but only 2 items, it should still measure its width to fit 3 items, not 2.
4. Any following calls to onMeasure(int, int) will run onLayoutChildren(Recycler, State) with isMeasuring() set to true and isPreLayout() set to false. RecyclerView will take care of which views are actually added / removed / moved / changed for animations so that the LayoutManager should not worry about them and handle each onLayoutChildren(Recycler, State) call as if it is the last one.
5. When measure is complete and RecyclerView's onLayout(boolean, int, int, int, int) method is called, RecyclerView checks whether it already did layout calculations during the measure pass and if so, it re-uses that information. It may still decide to call onLayoutChildren(Recycler, State) if the last measure spec was different from the final dimensions or adapter contents have changed between the measure call and the layout call.
6. Finally, animations are calculated and run as usual.

offsetChildrenHorizontal

void offsetChildrenHorizontal (int dx)

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

offsetChildrenVertical

void offsetChildrenVertical (int dy)

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

onDetachedFromWindow

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.

onFocusSearchFailed

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.

onInitializeAccessibilityEvent

void onInitializeAccessibilityEvent (AccessibilityEvent event)

onInitializeAccessibilityNodeInfoForItem

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.

onItemsAdded

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

void onItemsChanged (RecyclerView recyclerView)

Called in response to a call to notifyDataSetChanged() or swapAdapter(Adapter, boolean) ()} and signals that the the entire data set has changed.

onItemsMoved

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

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

Called when items have been removed from the adapter.

onItemsUpdated

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

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.

onLayoutCompleted

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.

onRestoreInstanceState

void onRestoreInstanceState (Parcelable state)

onSaveInstanceState

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.

onScrollStateChanged

void onScrollStateChanged (int state)

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

scrollHorizontallyBy

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.

scrollToPosition

void scrollToPosition (int position)

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

scrollToPositionWithOffset

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).

scrollVerticallyBy

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.

setGapStrategy

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.

setMeasuredDimension

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 only called if a LayoutManager returns true from isAutoMeasureEnabled() and it is called after the RecyclerView calls onLayoutChildren(Recycler, State) in the execution of onMeasure(int, int).

This method must 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.

setOrientation

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.

setReverseLayout

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.

setSpanCount

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.

smoothScrollToPosition

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).

supportsPredictiveItemAnimations

boolean supportsPredictiveItemAnimations ()

Returns whether this LayoutManager supports "predictive item animations".

"Predictive item animations" are automatically created animations that show where items came from, and where they are going to, as items are added, removed, or moved within a layout.

A LayoutManager wishing to support predictive item animations must override this method to return true (the default implementation returns false) and must obey certain behavioral contracts outlined in onLayoutChildren(Recycler, State).

Whether item animations actually occur in a RecyclerView is actually determined by both 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 only "simple item animations" will be enabled in the RecyclerView, in which views whose position are changing are simply faded in/out. If the RecyclerView has a non-null ItemAnimator and this method returns true, then predictive item animations will be enabled in the RecyclerView.