PagerSnapHelper

public class PagerSnapHelper extends SnapHelper

java.lang.Object
   ↳ androidx.recyclerview.widget.RecyclerView.OnFlingListener
     ↳ androidx.recyclerview.widget.SnapHelper
       ↳ androidx.recyclerview.widget.PagerSnapHelper

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

PagerSnapHelper can help achieve a similar behavior to androidx.viewpager.widget.ViewPager. Set both RecyclerView and the items of the RecyclerView.Adapter to have MATCH_PARENT height and width and then attach PagerSnapHelper to the RecyclerView using attachToRecyclerView.

Summary

Public constructors

Public methods
@Nullable int[]
calculateDistanceToFinalSnap(
    @NonNull RecyclerView.LayoutManager layoutManager,
    @NonNull View targetView
)

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

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

Override to provide a particular adapter target position for snapping.

Protected methods
@Nullable RecyclerView.SmoothScroller

Creates a scroller to be used in the snapping implementation.

Inherited methods
From androidx.recyclerview.widget.SnapHelper
void

Attaches the SnapHelper to the provided RecyclerView, by calling setOnFlingListener.
int[]
calculateScrollDistance(int velocityX, int velocityY)

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

This method is deprecated.

use createScroller instead.
boolean
onFling(int velocityX, int velocityY)

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

Public constructors

PagerSnapHelper

Added in 1.0.0
public PagerSnapHelper()

Public methods

calculateDistanceToFinalSnap

Added in 1.4.0
public @Nullable int[] calculateDistanceToFinalSnap(
    @NonNull RecyclerView.LayoutManager layoutManager,
    @NonNull View targetView
)

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
@NonNull RecyclerView.LayoutManager layoutManager

the RecyclerView.LayoutManager associated with the attached RecyclerView
@NonNull View targetView

the target view that is chosen as the view to snap
Returns
@Nullable 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.

findSnapView

Added in 1.4.0
public @Nullable View findSnapView(RecyclerView.LayoutManager layoutManager)

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
RecyclerView.LayoutManager layoutManager

the RecyclerView.LayoutManager associated with the attached RecyclerView
Returns
@Nullable View

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

findTargetSnapPosition

Added in 1.4.0
public int findTargetSnapPosition(
    RecyclerView.LayoutManager layoutManager,
    int velocityX,
    int velocityY
)

Override to provide a particular adapter target position for snapping.

Parameters
RecyclerView.LayoutManager layoutManager

the RecyclerView.LayoutManager associated with the attached RecyclerView
int velocityX

fling velocity on the horizontal axis
int velocityY

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

Protected methods

createScroller

protected @Nullable RecyclerView.SmoothScroller createScroller(@NonNull RecyclerView.LayoutManager layoutManager)

Creates a scroller to be used in the snapping implementation.

Parameters
@NonNull RecyclerView.LayoutManager layoutManager

The RecyclerView.LayoutManager associated with the attached RecyclerView.
Returns
@Nullable RecyclerView.SmoothScroller

a RecyclerView.SmoothScroller which will handle the scrolling.