SmoothScroller

Kotlin |Java

abstract class SmoothScroller

kotlin.Any
↳	androidx.recyclerview.widget.RecyclerView.SmoothScroller

Known Direct Subclasses

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.

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 LayoutManager#startSmoothScroll(SmoothScroller).

Summary

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

Public constructors
`<init>()`

Public methods
open PointF?	`computeScrollVectorForPosition(targetPosition: Int)` Compute the scroll vector for a given target position.
open View!	`findViewByPosition(position: Int)`
open Int	`getChildCount()`
open Int	`getChildPosition(view: View!)`
open RecyclerView.LayoutManager?	`getLayoutManager()`
open Int	`getTargetPosition()` Returns the adapter position of the target item
open Unit	`instantScrollToPosition(position: Int)`
open Boolean	`isPendingInitialRun()` Returns true if SmoothScroller has been started but has not received the first animation callback yet.
open Boolean	`isRunning()`
open Unit	`setTargetPosition(targetPosition: Int)`

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

Public constructors

<init>

SmoothScroller()

Public methods

computeScrollVectorForPosition

@Nullable open fun computeScrollVectorForPosition(targetPosition: Int): PointF?

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

Return
`PointF?`	the scroll vector for a given target position

findViewByPosition

open fun findViewByPosition(position: Int): View!

See Also

RecyclerView.LayoutManager#findViewByPosition(int)

getChildCount

open fun getChildCount(): Int

See Also

RecyclerView.LayoutManager#getChildCount()

getChildPosition

open fun getChildPosition(view: View!): Int

See Also

RecyclerView#getChildLayoutPosition(android.view.View)

getLayoutManager

@Nullable open fun getLayoutManager(): RecyclerView.LayoutManager?

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

getTargetPosition

open fun getTargetPosition(): Int

Returns the adapter position of the target item

Return
`Int`	Adapter position of the target item or `RecyclerView#NO_POSITION` if no target view is set.

instantScrollToPosition

open fun instantScrollToPosition(position: Int): Unit

Deprecated: Use Action#jumpTo(int).

See Also

RecyclerView#scrollToPosition(int)

isPendingInitialRun

open fun isPendingInitialRun(): Boolean

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

Return
`Boolean`	True if this SmoothScroller is waiting to start

isRunning

open fun isRunning(): Boolean

Return
`Boolean`	True if SmoothScroller is currently active

setTargetPosition

open fun setTargetPosition(targetPosition: Int): Unit

Protected methods

normalize

protected open fun normalize(@NonNull scrollVector: PointF): Unit

Normalizes the vector.

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

onChildAttachedToWindow

protected open fun onChildAttachedToWindow(child: View!): Unit

onSeekTargetStep

protected abstract fun onSeekTargetStep(
    @Px dx: Int, 
    @Px dy: Int, 
    @NonNull state: RecyclerView.State, 
    @NonNull action: RecyclerView.SmoothScroller.Action
): Unit

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 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 fun onStart(): Unit

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

onStop

protected abstract fun onStop(): Unit

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

See Also

#stop()

onTargetFound

protected abstract fun onTargetFound(
    @NonNull targetView: View, 
    @NonNull state: RecyclerView.State, 
    @NonNull action: RecyclerView.SmoothScroller.Action
): Unit

Called when the target position is laid out. This is the last callback SmoothScroller will receive and it should update the provided 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 fun stop(): Unit

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