SnapHelper

abstract class SnapHelper : RecyclerView.OnFlingListener

kotlin.Any
   ↳ androidx.recyclerview.widget.RecyclerView.OnFlingListener
     ↳ androidx.recyclerview.widget.SnapHelper
Known direct subclasses
LinearSnapHelper

Implementation of the SnapHelper supporting snapping in either vertical or horizontal orientation.
PagerSnapHelper

Implementation of the SnapHelper supporting pager style snapping in either vertical or horizontal orientation.

Class intended to support snapping for a RecyclerView.

SnapHelper tries to handle fling as well but for this to work properly, the RecyclerView.LayoutManager must implement the RecyclerView.SmoothScroller.ScrollVectorProvider interface or you should override onFling and handle fling manually.

Summary

Public constructors

Public functions
Unit

Attaches the SnapHelper to the provided RecyclerView, by calling setOnFlingListener.
abstract IntArray<Int>?
calculateDistanceToFinalSnap(
    layoutManager: RecyclerView.LayoutManager,
    targetView: View
)

Override this method to snap to a particular point within the target view or the container view on any axis.
IntArray<Int>!
calculateScrollDistance(velocityX: Int, velocityY: Int)

Calculated the estimated scroll distance in each direction given velocities on both axes.
abstract View?

Override this method to provide a particular target view for snapping.
abstract Int
findTargetSnapPosition(
    layoutManager: RecyclerView.LayoutManager!,
    velocityX: Int,
    velocityY: Int
)

Override to provide a particular adapter target position for snapping.
Boolean
onFling(velocityX: Int, velocityY: Int)

Override this to handle a fling given the velocities in both x and y directions.

Protected functions
RecyclerView.SmoothScroller?

Creates a scroller to be used in the snapping implementation.
LinearSmoothScroller?

This function is deprecated.

use createScroller instead.

Public constructors

SnapHelper

Added in 1.0.0
SnapHelper()

Public functions

attachToRecyclerView

Added in 1.0.0
fun attachToRecyclerView(recyclerView: RecyclerView?): Unit

Attaches the SnapHelper to the provided RecyclerView, by calling setOnFlingListener. You can call this method with null to detach it from the current RecyclerView.

Parameters
recyclerView: RecyclerView?

The RecyclerView instance to which you want to add this helper or null if you want to remove SnapHelper from the current RecyclerView.
Throws
java.lang.IllegalArgumentException

if there is already a RecyclerView.OnFlingListener attached to the provided RecyclerView.
java.lang.IllegalStateException

calculateDistanceToFinalSnap

Added in 1.0.0
abstract fun calculateDistanceToFinalSnap(
    layoutManager: RecyclerView.LayoutManager,
    targetView: View
): IntArray<Int>?

Override this method to snap to a particular point within the target view or the container view on any axis.

This method is called when the SnapHelper has intercepted a fling and it needs to know the exact distance required to scroll by in order to snap to the target view.

Parameters
layoutManager: RecyclerView.LayoutManager

the RecyclerView.LayoutManager associated with the attached RecyclerView
targetView: View

the target view that is chosen as the view to snap
Returns
IntArray<Int>?

the output coordinates the put the result into. out[0] is the distance on horizontal axis and out[1] is the distance on vertical axis.

calculateScrollDistance

Added in 1.0.0
fun calculateScrollDistance(velocityX: Int, velocityY: Int): IntArray<Int>!

Calculated the estimated scroll distance in each direction given velocities on both axes.

Parameters
velocityX: Int

Fling velocity on the horizontal axis.
velocityY: Int

Fling velocity on the vertical axis.
Returns
IntArray<Int>!

array holding the calculated distances in x and y directions respectively.

findSnapView

Added in 1.0.0
abstract fun findSnapView(layoutManager: RecyclerView.LayoutManager!): View?

Override this method to provide a particular target view for snapping.

This method is called when the SnapHelper is ready to start snapping and requires a target view to snap to. It will be explicitly called when the scroll state becomes idle after a scroll. It will also be called when the SnapHelper is preparing to snap after a fling and requires a reference view from the current set of child views.

If this method returns null, SnapHelper will not snap to any view.

Parameters
layoutManager: RecyclerView.LayoutManager!

the RecyclerView.LayoutManager associated with the attached RecyclerView
Returns
View?

the target view to which to snap on fling or end of scroll

findTargetSnapPosition

Added in 1.0.0
abstract fun findTargetSnapPosition(
    layoutManager: RecyclerView.LayoutManager!,
    velocityX: Int,
    velocityY: Int
): Int

Override to provide a particular adapter target position for snapping.

Parameters
layoutManager: RecyclerView.LayoutManager!

the RecyclerView.LayoutManager associated with the attached RecyclerView
velocityX: Int

fling velocity on the horizontal axis
velocityY: Int

fling velocity on the vertical axis
Returns
Int

the target adapter position to you want to snap or NO_POSITION if no snapping should happen

onFling

Added in 1.4.0-rc01
fun onFling(velocityX: Int, velocityY: Int): Boolean

Override this to handle a fling given the velocities in both x and y directions. Note that this method will only be called if the associated LayoutManager supports scrolling and the fling is not handled by nested scrolls first.

Parameters
velocityX: Int

the fling velocity on the X axis
velocityY: Int

the fling velocity on the Y axis
Returns
Boolean

true if the fling was handled, false otherwise.

Protected functions

createScroller

Added in 1.0.0
protected fun createScroller(layoutManager: RecyclerView.LayoutManager): RecyclerView.SmoothScroller?

Creates a scroller to be used in the snapping implementation.

Parameters
layoutManager: RecyclerView.LayoutManager

The RecyclerView.LayoutManager associated with the attached RecyclerView.
Returns
RecyclerView.SmoothScroller?

a RecyclerView.SmoothScroller which will handle the scrolling.

createSnapScroller

Added in 1.0.0
Deprecated in 1.0.0
protected fun createSnapScroller(layoutManager: RecyclerView.LayoutManager): LinearSmoothScroller?

Creates a scroller to be used in the snapping implementation.

Parameters
layoutManager: RecyclerView.LayoutManager

The RecyclerView.LayoutManager associated with the attached RecyclerView.
Returns
LinearSmoothScroller?

a LinearSmoothScroller which will handle the scrolling.