java.lang.Object | |
↳ | android.support.v7.widget.RecyclerView.LayoutManager |
Known Direct Subclasses |
A LayoutManager
is responsible for measuring and positioning item views
within a RecyclerView
as well as determining the policy for when to recycle
item views that are no longer visible to the user. By changing the LayoutManager
a RecyclerView
can be used to implement a standard vertically scrolling list,
a uniform grid, staggered grids, horizontally scrolling collections and more. Several stock
layout managers are provided for general use.
Public Constructors | |||||||||||
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Public Methods | |||||||||||
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Add a view to the currently attached RecyclerView if needed.
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Add a view to the currently attached RecyclerView if needed.
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Reattach a previously
detached view. | |||||||||||
Reattach a previously
detached view. | |||||||||||
Reattach a previously
detached view. | |||||||||||
Query if horizontal scrolling is currently supported.
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Query if vertical scrolling is currently supported.
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Determines the validity of the supplied LayoutParams object.
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Override this method if you want to support scroll bars. | |||||||||||
Override this method if you want to support scroll bars. | |||||||||||
Override this method if you want to support scroll bars. | |||||||||||
Override this method if you want to support scroll bars. | |||||||||||
Override this method if you want to support scroll bars. | |||||||||||
Override this method if you want to support scroll bars. | |||||||||||
Temporarily detach and scrap all currently attached child views.
| |||||||||||
Detach a child view and add it to a
Recycler's scrap heap. | |||||||||||
Detach a child view and add it to a
Recycler's scrap heap. | |||||||||||
Temporarily detach a child view.
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Temporarily detach a child view.
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Finds the view which represents the given adapter position. | |||||||||||
Create a default
LayoutParams object for a child of the RecyclerView. | |||||||||||
Create a LayoutParams object suitable for this LayoutManager, copying relevant
values from the supplied LayoutParams object if possible.
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Create a LayoutParams object suitable for this LayoutManager from
an inflated layout resource.
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Return the child view at the given index
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Return the current number of child views attached to the parent RecyclerView.
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Calculate a MeasureSpec value for measuring a child view in one dimension.
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Returns the bottom edge of the given child view within its parent, offset by any applied
ItemDecorations . | |||||||||||
Returns the left edge of the given child view within its parent, offset by any applied
ItemDecorations . | |||||||||||
Returns the measured height of the given child, plus the additional size of
any insets applied by
ItemDecorations . | |||||||||||
Returns the measured width of the given child, plus the additional size of
any insets applied by
ItemDecorations . | |||||||||||
Returns the right edge of the given child view within its parent, offset by any applied
ItemDecorations . | |||||||||||
Returns the top edge of the given child view within its parent, offset by any applied
ItemDecorations . | |||||||||||
Return the height of the parent RecyclerView
| |||||||||||
Return the number of items in the adapter bound to the parent RecyclerView
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Returns the resolved layout direction for this RecyclerView.
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Return the bottom padding of the parent RecyclerView
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Return the end padding of the parent RecyclerView
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Return the left padding of the parent RecyclerView
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Return the right padding of the parent RecyclerView
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Return the start padding of the parent RecyclerView
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Return the top padding of the parent RecyclerView
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Returns the adapter position of the item represented by the given View.
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Return the width of the parent RecyclerView
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Returns true if the RecyclerView this LayoutManager is bound to has or contains focus.
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Returns true if the RecyclerView this LayoutManager is bound to has focus.
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Lay out the given child view within the RecyclerView using coordinates that
include any current
ItemDecorations . | |||||||||||
Measure a child view using standard measurement policy, taking the padding
of the parent RecyclerView and any added item decorations into account.
| |||||||||||
Measure a child view using standard measurement policy, taking the padding
of the parent RecyclerView, any added item decorations and the child margins
into account.
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Offset all child views attached to the parent RecyclerView by dx pixels along
the horizontal axis.
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Offset all child views attached to the parent RecyclerView by dy pixels along
the vertical axis.
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Called if the RecyclerView this LayoutManager is bound to has a different adapter set.
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Called to populate focusable views within the RecyclerView.
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Called when this LayoutManager is both attached to a RecyclerView and that RecyclerView
is attached to a window.
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Called when this LayoutManager is detached from its parent RecyclerView or when
its parent RecyclerView is detached from its window.
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Called when searching for a focusable view in the given direction has failed
for the current content of the RecyclerView.
| |||||||||||
This method gives a LayoutManager an opportunity to intercept the initial focus search
before the default behavior of
FocusFinder is used. | |||||||||||
Called when items have been added to the adapter.
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Called when items have been removed from the adapter.
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Lay out all relevant child views from the given adapter.
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Measure the attached RecyclerView.
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Called when a descendant view of the RecyclerView requests focus.
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Called when the LayoutManager should save its state. | |||||||||||
Remove all views from the currently attached RecyclerView.
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Remove a child view and recycle it using the given Recycler.
| |||||||||||
Remove a child view and recycle it using the given Recycler.
| |||||||||||
Finish removing a view that was previously temporarily
detached . | |||||||||||
Remove a view from the currently attached RecyclerView if needed.
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Remove a view from the currently attached RecyclerView if needed.
| |||||||||||
Called when a child of the RecyclerView wants a particular rectangle to be positioned
onto the screen.
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Calls
RecyclerView#requestLayout on the underlying RecyclerView
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Scroll horizontally by dx pixels in screen coordinates and return the distance traveled.
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Scroll to the specified adapter position.
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Scroll vertically by dy pixels in screen coordinates and return the distance traveled.
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Set the measured dimensions of the
host RecyclerView. | |||||||||||
Smooth scroll to the specified adapter position. | |||||||||||
Starts a smooth scroll using the provided SmoothScroller. | |||||||||||
Returns whether this LayoutManager supports automatic item animations.
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[Expand]
Inherited Methods | |||||||||||
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From class
java.lang.Object
|
Add a view to the currently attached RecyclerView if needed. LayoutManagers should
use this method to add views obtained from a RecyclerView.Recycler
using
getViewForPosition(int)
.
child | View to add |
---|---|
index | Index to add child at |
Add a view to the currently attached RecyclerView if needed. LayoutManagers should
use this method to add views obtained from a RecyclerView.Recycler
using
getViewForPosition(int)
.
child | View to add |
---|
Reattach a previously detached
view.
This method should not be used to reattach views that were previously
detachAndScrapView(android.view.View, RecyclerView.Recycler)
scrapped}.
child | Child to reattach |
---|
Reattach a previously detached
view.
This method should not be used to reattach views that were previously
detachAndScrapView(android.view.View, RecyclerView.Recycler)
scrapped}.
child | Child to reattach |
---|---|
index | Intended child index for child |
lp | LayoutParams for child |
Reattach a previously detached
view.
This method should not be used to reattach views that were previously
detachAndScrapView(android.view.View, RecyclerView.Recycler)
scrapped}.
child | Child to reattach |
---|---|
index | Intended child index for child |
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.
lp | LayoutParams object to check |
---|
Override this method if you want to support scroll bars.
Read computeHorizontalScrollExtent()
for details.
Default implementation returns 0.
state | Current state of RecyclerView |
---|
Override this method if you want to support scroll bars.
Read computeHorizontalScrollOffset()
for details.
Default implementation returns 0.
state | Current State of RecyclerView where you can find total item count |
---|
Override this method if you want to support scroll bars.
Read computeHorizontalScrollRange()
for details.
Default implementation returns 0.
state | Current State of RecyclerView where you can find total item count |
---|
Override this method if you want to support scroll bars.
Read computeVerticalScrollExtent()
for details.
Default implementation returns 0.
state | Current state of RecyclerView |
---|
Override this method if you want to support scroll bars.
Read computeVerticalScrollOffset()
for details.
Default implementation returns 0.
state | Current State of RecyclerView where you can find total item count |
---|
Override this method if you want to support scroll bars.
Read computeVerticalScrollRange()
for details.
Default implementation returns 0.
state | Current State of RecyclerView where you can find total item count |
---|
Temporarily detach and scrap all currently attached child views. Views will be scrapped into the given Recycler. The Recycler may prefer to reuse scrap views before other views that were previously recycled.
recycler | Recycler to scrap views into |
---|
Detach a child view and add it to a Recycler's
scrap heap.
Scrapping a view allows it to be rebound and reused to show updated or different data.
child | Child to detach and scrap |
---|---|
recycler | Recycler to deposit the new scrap view into |
Detach a child view and add it to a Recycler's
scrap heap.
Scrapping a view allows it to be rebound and reused to show updated or different data.
index | Index of child to detach and scrap |
---|---|
recycler | Recycler to deposit the new scrap view into |
Temporarily detach a child view.
LayoutManagers may want to perform a lightweight detach operation to rearrange
views currently attached to the RecyclerView. Generally LayoutManager implementations
will want to use detachAndScrapView(android.view.View, RecyclerView.Recycler)
so that the detached view may be rebound and reused.
If a LayoutManager uses this method to detach a view, it must
reattach
or fully remove
the detached view
before the LayoutManager entry point method called by RecyclerView returns.
child | Child to detach |
---|
Temporarily detach a child view.
LayoutManagers may want to perform a lightweight detach operation to rearrange
views currently attached to the RecyclerView. Generally LayoutManager implementations
will want to use detachAndScrapView(android.view.View, RecyclerView.Recycler)
so that the detached view may be rebound and reused.
If a LayoutManager uses this method to detach a view, it must
reattach
or fully remove
the detached view
before the LayoutManager entry point method called by RecyclerView returns.
index | Index of the child to detach |
---|
Finds the view which represents the given adapter 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.
position | Position of the item in adapter |
---|
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, 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)
.
lp | Source LayoutParams object to copy values from |
---|
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)
.
c | Context for obtaining styled attributes |
---|---|
attrs | AttributeSet describing the supplied arguments |
Return the child view at the given index
index | Index of child to return |
---|
Return the current number of child views attached to the parent RecyclerView. This does not include child views that were temporarily detached and/or scrapped.
Calculate a MeasureSpec value for measuring a child view in one dimension.
parentSize | Size of the parent view where the child will be placed |
---|---|
padding | Total space currently consumed by other elements of parent |
childDimension | Desired size of the child view, or MATCH_PARENT/WRAP_CONTENT. Generally obtained from the child view's LayoutParams |
canScroll | true if the parent RecyclerView can scroll in this dimension |
Returns the bottom edge of the given child view within its parent, offset by any applied
ItemDecorations
.
child | Child to query |
---|
Returns the left edge of the given child view within its parent, offset by any applied
ItemDecorations
.
child | Child to query |
---|
Returns the measured height of the given child, plus the additional size of
any insets applied by ItemDecorations
.
child | Child view to query |
---|
ItemDecoration
insetsReturns the measured width of the given child, plus the additional size of
any insets applied by ItemDecorations
.
child | Child view to query |
---|
ItemDecoration
insetsReturns the right edge of the given child view within its parent, offset by any applied
ItemDecorations
.
child | Child to query |
---|
Returns the top edge of the given child view within its parent, offset by any applied
ItemDecorations
.
child | Child to query |
---|
Return the height of the parent RecyclerView
Return the number of items in the adapter bound to the parent RecyclerView
Returns the resolved layout direction for this RecyclerView.
LAYOUT_DIRECTION_RTL
if the layout
direction is RTL or returns
LAYOUT_DIRECTION_LTR
if the layout direction
is not RTL.
Return the bottom padding of the parent RecyclerView
Return the end padding of the parent RecyclerView
Return the left padding of the parent RecyclerView
Return the right padding of the parent RecyclerView
Return the start padding of the parent RecyclerView
Return the top padding of the parent RecyclerView
Returns the adapter position of the item represented by the given View.
view | The view to query |
---|
Return the width of the parent RecyclerView
Returns true if the RecyclerView this LayoutManager is bound to has or contains focus.
Returns true if the RecyclerView this LayoutManager is bound to has focus.
Lay out the given child view within the RecyclerView using coordinates that
include any current ItemDecorations
.
LayoutManagers should prefer working in sizes and coordinates that include item decoration insets whenever possible. This allows the LayoutManager to effectively ignore decoration insets within measurement and layout code. See the following methods:
child | Child to lay out |
---|---|
left | Left edge, with item decoration insets included |
top | Top edge, with item decoration insets included |
right | Right edge, with item decoration insets included |
bottom | Bottom edge, with item decoration insets included |
Measure a child view using standard measurement policy, taking the padding of the parent RecyclerView and any added item decorations into account.
If the RecyclerView can be scrolled in either dimension the caller may pass 0 as the widthUsed or heightUsed parameters as they will be irrelevant.
child | Child view to measure |
---|---|
widthUsed | Width in pixels currently consumed by other views, if relevant |
heightUsed | Height in pixels currently consumed by other views, if relevant |
Measure a child view using standard measurement policy, taking the padding of the parent RecyclerView, any added item decorations and the child margins into account.
If the RecyclerView can be scrolled in either dimension the caller may pass 0 as the widthUsed or heightUsed parameters as they will be irrelevant.
child | Child view to measure |
---|---|
widthUsed | Width in pixels currently consumed by other views, if relevant |
heightUsed | Height in pixels currently consumed by other views, if relevant |
Offset all child views attached to the parent RecyclerView by dx pixels along the horizontal axis.
dx | Pixels to offset by |
---|
Offset all child views attached to the parent RecyclerView by dy pixels along the vertical axis.
dy | Pixels to offset by |
---|
Called if the RecyclerView this LayoutManager is bound to has a different adapter set. The LayoutManager may use this opportunity to clear caches and configure state such that it can relayout appropriately with the new data and potentially new view types.
The default implementation removes all currently attached views.
oldAdapter | The previous adapter instance. Will be null if there was previously no adapter. |
---|---|
newAdapter | The new adapter instance. Might be null if
setAdapter(RecyclerView.Adapter) is called with null .
|
Called to populate focusable views within the RecyclerView.
The LayoutManager implementation should return true
if the default
behavior of addFocusables(java.util.ArrayList, int)
should be
suppressed.
The default implementation returns false
to trigger RecyclerView
to fall back to the default ViewGroup behavior.
recyclerView | The RecyclerView hosting this LayoutManager |
---|---|
views | List of output views. This method should add valid focusable views to this list. |
direction | One of FOCUS_UP , FOCUS_DOWN ,
FOCUS_LEFT , FOCUS_RIGHT ,
FOCUS_BACKWARD , FOCUS_FORWARD |
focusableMode | The type of focusables to be added. |
Called when this LayoutManager is both attached to a RecyclerView and that RecyclerView is attached to a window.
Subclass implementations should always call through to the superclass implementation.
view | The RecyclerView this LayoutManager is bound to |
---|
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.
view | The RecyclerView this LayoutManager is bound to |
---|
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. The default implementation returns null.
focused | The currently focused view |
---|---|
direction | One of FOCUS_UP , FOCUS_DOWN ,
FOCUS_LEFT , FOCUS_RIGHT ,
FOCUS_BACKWARD , FOCUS_FORWARD
or 0 for not applicable |
recycler | The recycler to use for obtaining views for currently offscreen items |
state | Transient state of RecyclerView |
This method gives a LayoutManager an opportunity to intercept the initial focus search
before the default behavior of FocusFinder
is used. If this method returns
null FocusFinder will attempt to find a focusable child view. If it fails
then onFocusSearchFailed(View, int, RecyclerView.Recycler, RecyclerView.State)
will be called to give the LayoutManager an opportunity to add new views for items
that did not have attached views representing them. The LayoutManager should not add
or remove views from this method.
focused | The currently focused view |
---|---|
direction | One of FOCUS_UP , FOCUS_DOWN ,
FOCUS_LEFT , FOCUS_RIGHT ,
FOCUS_BACKWARD , FOCUS_FORWARD |
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 items have been removed from the adapter.
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
simple fade views in and out, whether they are actuall 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.
recycler | Recycler to use for fetching potentially cached views for a position |
---|---|
state | Transient state of RecyclerView |
Measure the attached RecyclerView. Implementations must call
setMeasuredDimension(int, int)
before returning.
The default implementation will handle EXACTLY measurements and respect the minimum width and height properties of the host RecyclerView if measured as UNSPECIFIED. AT_MOST measurements will be treated as EXACTLY and the RecyclerView will consume all available space.
recycler | Recycler |
---|---|
state | Transient state of RecyclerView |
widthSpec | Width View.MeasureSpec |
heightSpec | Height View.MeasureSpec
|
Called when a descendant view of the RecyclerView requests focus.
A LayoutManager wishing to keep focused views aligned in a specific portion of the view may implement that behavior in an override of this method.
If the LayoutManager executes different behavior that should override the default behavior of scrolling the focused child on screen instead of running alongside it, this method should return true.
parent | The RecyclerView hosting this LayoutManager |
---|---|
child | Direct child of the RecyclerView containing the newly focused view |
focused | The newly focused view. This may be the same view as child |
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.
Remove all views from the currently attached RecyclerView. This will not recycle any of the affected views; the LayoutManager is responsible for doing so if desired.
Remove a child view and recycle it using the given Recycler.
child | Child to remove and recycle |
---|---|
recycler | Recycler to use to recycle child |
Remove a child view and recycle it using the given Recycler.
index | Index of child to remove and recycle |
---|---|
recycler | Recycler to use to recycle child |
Finish removing a view that was previously temporarily
detached
.
child | Detached child to remove |
---|
Remove a view from the currently attached RecyclerView if needed. LayoutManagers should
use this method to completely remove a child view that is no longer needed.
LayoutManagers should strongly consider recycling removed views using
recycleView(android.view.View)
.
child | View to remove |
---|
Remove a view from the currently attached RecyclerView if needed. LayoutManagers should
use this method to completely remove a child view that is no longer needed.
LayoutManagers should strongly consider recycling removed views using
recycleView(android.view.View)
.
index | Index of the child view to remove |
---|
Called when a child of the RecyclerView wants a particular rectangle to be positioned
onto the screen. See requestChildRectangleOnScreen(android.view.View, android.graphics.Rect, boolean)
for more details.
The base implementation will attempt to perform a standard programmatic scroll to bring the given rect into view, within the padded area of the RecyclerView.
child | The direct child making the request. |
---|---|
rect | The rectangle in the child's coordinates the child wishes to be on the screen. |
immediate | True to forbid animated or delayed scrolling, false otherwise |
Calls RecyclerView#requestLayout
on the underlying RecyclerView
Scroll horizontally by dx pixels in screen coordinates and return the distance traveled. The default implementation does nothing and returns 0.
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 position |
state | Transient state of RecyclerView |
Math.abs(result)
may be less than dx if a boundary was reached.
Scroll to the specified adapter position. Actual position of the item on the screen depends on the LayoutManager implementation.
position | Scroll to this adapter position. |
---|
Scroll vertically by dy pixels in screen coordinates and return the distance traveled. The default implementation does nothing and returns 0.
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 position |
state | Transient state of RecyclerView |
Math.abs(result)
may be less than dy if a boundary was reached.
Set the measured dimensions
of the
host RecyclerView.
widthSize | Measured width |
---|---|
heightSize | Measured height |
Smooth scroll to the specified adapter position.
To support smooth scrolling, override this method, create your RecyclerView.SmoothScroller
instance and call startSmoothScroll(SmoothScroller)
.
recyclerView | The RecyclerView to which this layout manager is attached |
---|---|
state | Current State of RecyclerView |
position | Scroll to this adapter position. |
Starts a smooth scroll using the provided SmoothScroller.
Calling this method will cancel any previous smooth scroll request.
smoothScroller | Unstance which defines how smooth scroll should be animated |
---|
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.