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RecyclerView.SmoothScroller

public static abstract class RecyclerView.SmoothScroller
extends Object

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


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).

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

RecyclerView.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

Public constructors

RecyclerView.SmoothScroller

public RecyclerView.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

getChildCount

public int getChildCount ()

Returns
int

getChildPosition

public int getChildPosition (View view)

Parameters
view View

Returns
int

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

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:

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).