Summary: Nested Classes | Ctors | Methods | Protected Methods | Inherited Methods

RecyclerView.SmoothScroller

Kotlin |Java

public static abstract class RecyclerView.SmoothScroller
extends Object

java.lang.Object
↳	androidx.recyclerview.widget.RecyclerView.SmoothScroller

Known direct subclasses LinearSmoothScroller LinearSmoothScroller RecyclerView.SmoothScroller implementation which uses a LinearInterpolator until the target position becomes a child of the RecyclerView and then uses a DecelerateInterpolator to slowly approach to target position.

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Base class for smooth scrolling. Handles basic tracking of the target view position and provides methods to trigger a programmatic scroll.

An instance of SmoothScroller is only intended to be used once. You should create a new instance for each call to RecyclerView.LayoutManager.startSmoothScroll(SmoothScroller).

See also:

• LinearSmoothScroller

Summary

Nested classes
class	RecyclerView.SmoothScroller.Action Holds information about a smooth scroll request by a RecyclerView.SmoothScroller.
interface	RecyclerView.SmoothScroller.ScrollVectorProvider An interface which is optionally implemented by custom RecyclerView.LayoutManager to provide a hint to a RecyclerView.SmoothScroller about the location of the target position.

Public constructors
SmoothScroller()

Public methods
PointF	computeScrollVectorForPosition(int targetPosition) Compute the scroll vector for a given target position.
View	findViewByPosition(int position)
int	getChildCount()
int	getChildPosition(View view)
RecyclerView.LayoutManager	getLayoutManager()
int	getTargetPosition() Returns the adapter position of the target item
void	instantScrollToPosition(int position) This method is deprecated. Use RecyclerView.SmoothScroller.Action.jumpTo(int).
boolean	isPendingInitialRun() Returns true if SmoothScroller has been started but has not received the first animation callback yet.
boolean	isRunning()
void	setTargetPosition(int targetPosition)

Protected methods
void	normalize(PointF scrollVector) Normalizes the vector.
void	onChildAttachedToWindow(View child)
abstract void	onSeekTargetStep(int dx, int dy, RecyclerView.State state, RecyclerView.SmoothScroller.Action action) RecyclerView will call this method each time it scrolls until it can find the target position in the layout.
abstract void	onStart() Called when smooth scroll is started.
abstract void	onStop() Called when smooth scroller is stopped.
abstract void	onTargetFound(View targetView, RecyclerView.State state, RecyclerView.SmoothScroller.Action action) Called when the target position is laid out.
final void	stop() Stops running the SmoothScroller in each animation callback.

Inherited methods
From class java.lang.Object Object clone() boolean equals(Object arg0) void finalize() final Class<?> getClass() int hashCode() final void notify() final void notifyAll() String toString() final void wait(long arg0, int arg1) final void wait(long arg0) final void wait()

Public constructors

SmoothScroller

public SmoothScroller ()

Public methods

computeScrollVectorForPosition

public PointF computeScrollVectorForPosition (int targetPosition)

Compute the scroll vector for a given target position.

This method can return null if the layout manager cannot calculate a scroll vector for the given position (e.g. it has no current scroll position).

Parameters
targetPosition	int: the position to which the scroller is scrolling

Returns
PointF	the scroll vector for a given target position

findViewByPosition

public View findViewByPosition (int position)

Parameters
position	int

Returns
View

See also:

• RecyclerView.LayoutManager.findViewByPosition(int)

getChildCount

public int getChildCount ()

Returns
int

See also:

• RecyclerView.LayoutManager.getChildCount()

getChildPosition

public int getChildPosition (View view)

Parameters
view	View

Returns
int

See also:

• RecyclerView.getChildLayoutPosition(android.view.View)

getLayoutManager

public RecyclerView.LayoutManager getLayoutManager ()

Returns
RecyclerView.LayoutManager	The LayoutManager to which this SmoothScroller is attached. Will return null after the SmoothScroller is stopped.

getTargetPosition

public int getTargetPosition ()

Returns the adapter position of the target item

Returns
int	Adapter position of the target item or RecyclerView.NO_POSITION if no target view is set.

instantScrollToPosition

public void instantScrollToPosition (int position)

This method is deprecated.
Use RecyclerView.SmoothScroller.Action.jumpTo(int).

Parameters
position	int

See also:

• RecyclerView.scrollToPosition(int)

isPendingInitialRun

public boolean isPendingInitialRun ()

Returns true if SmoothScroller has been started but has not received the first animation callback yet.

Returns
boolean	True if this SmoothScroller is waiting to start

isRunning

public boolean isRunning ()

Returns
boolean	True if SmoothScroller is currently active

setTargetPosition

public void setTargetPosition (int targetPosition)

Parameters
targetPosition	int

Protected methods

normalize

protected void normalize (PointF scrollVector)

Normalizes the vector.

Parameters
scrollVector	PointF: The vector that points to the target scroll position

onChildAttachedToWindow

protected void onChildAttachedToWindow (View child)

Parameters
child	View

onSeekTargetStep

protected abstract void onSeekTargetStep (int dx, 
                int dy, 
                RecyclerView.State state, 
                RecyclerView.SmoothScroller.Action action)

RecyclerView will call this method each time it scrolls until it can find the target position in the layout.

SmoothScroller should check dx, dy and if scroll should be changed, update the provided RecyclerView.SmoothScroller.Action to define the next scroll.

Parameters
dx	int: Last scroll amount horizontally
dy	int: Last scroll amount vertically
state	RecyclerView.State: Transient state of RecyclerView
action	RecyclerView.SmoothScroller.Action: If you want to trigger a new smooth scroll and cancel the previous one, update this object.

onStart

protected abstract void onStart ()

Called when smooth scroll is started. This might be a good time to do setup.

onStop

protected abstract void onStop ()

Called when smooth scroller is stopped. This is a good place to cleanup your state etc.

See also:

• stop()

onTargetFound

protected abstract void onTargetFound (View targetView, 
                RecyclerView.State state, 
                RecyclerView.SmoothScroller.Action action)

Called when the target position is laid out. This is the last callback SmoothScroller will receive and it should update the provided RecyclerView.SmoothScroller.Action to define the scroll details towards the target view.

Parameters
targetView	View: The view element which render the target position.
state	RecyclerView.State: Transient state of RecyclerView
action	RecyclerView.SmoothScroller.Action: Action instance that you should update to define final scroll action towards the targetView

stop

protected final void stop ()

Stops running the SmoothScroller in each animation callback. Note that this does not cancel any existing RecyclerView.SmoothScroller.Action updated by onTargetFound(android.view.View, RecyclerView.State, SmoothScroller.Action) or onSeekTargetStep(int, int, RecyclerView.State, SmoothScroller.Action).