StaggeredGridLayoutManager

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
 

Does not do anything to hide gaps.

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

Creates a StaggeredGridLayoutManager with given parameters.

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

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

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

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.

Override this method if you want to support scroll bars.

Read computeHorizontalScrollExtent() for details.

Default implementation returns 0.

Override this method if you want to support scroll bars.

Read computeHorizontalScrollOffset() for details.

Default implementation returns 0.

Override this method if you want to support scroll bars.

Read computeHorizontalScrollRange() for details.

Default implementation returns 0.

Override this method if you want to support scroll bars.

Read computeVerticalScrollExtent() for details.

Default implementation returns 0.

Override this method if you want to support scroll bars.

Read computeVerticalScrollOffset() for details.

Default implementation returns 0.

Override this method if you want to support scroll bars.

Read computeVerticalScrollRange() for details.

Default implementation returns 0.

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.

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.

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.

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.

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).

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).

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).

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.

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 whether views are laid out in reverse order or not.

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

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.

Returns the number of spans laid out by StaggeredGridLayoutManager.

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.

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

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

Called when this LayoutManager is detached from its parent RecyclerView or when its parent RecyclerView is detached from its window.

Subclass implementations should always call through to the superclass implementation.

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

Default implementation adds basic positioning information about the item.

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.)

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

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.

Called when items have been removed from the adapter.

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

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.

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.

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

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

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

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).

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

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.

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.

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.

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.

Smooth scroll to the specified adapter position.

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

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.