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added in version 25.1.0
belongs to Maven artifact com.android.support:recyclerview-v7:27.0.0

SnapHelper

public abstract class SnapHelper
extends RecyclerView.OnFlingListener

java.lang.Object
   ↳ android.support.v7.widget.RecyclerView.OnFlingListener
     ↳ android.support.v7.widget.SnapHelper
Known Direct Subclasses


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(int, int) and handle fling manually.

Summary

Public constructors

SnapHelper()

Public methods

void attachToRecyclerView(RecyclerView recyclerView)

Attaches the SnapHelper to the provided RecyclerView, by calling setOnFlingListener(RecyclerView.OnFlingListener).

abstract int[] calculateDistanceToFinalSnap(RecyclerView.LayoutManager layoutManager, View targetView)

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

int[] calculateScrollDistance(int velocityX, int velocityY)

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

abstract View findSnapView(RecyclerView.LayoutManager layoutManager)

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

abstract int findTargetSnapPosition(RecyclerView.LayoutManager layoutManager, int velocityX, int velocityY)

Override to provide a particular adapter target position for snapping.

boolean onFling(int velocityX, int velocityY)

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

Protected methods

RecyclerView.SmoothScroller createScroller(RecyclerView.LayoutManager layoutManager)

Creates a scroller to be used in the snapping implementation.

LinearSmoothScroller createSnapScroller(RecyclerView.LayoutManager layoutManager)

This method was deprecated in API level 26.1.0. use createScroller(LayoutManager) instead.

Inherited methods

From class android.support.v7.widget.RecyclerView.OnFlingListener
From class java.lang.Object

Public constructors

SnapHelper

added in version 25.1.0
SnapHelper ()

Public methods

attachToRecyclerView

added in version 25.1.0
void attachToRecyclerView (RecyclerView recyclerView)

Attaches the SnapHelper to the provided RecyclerView, by calling setOnFlingListener(RecyclerView.OnFlingListener). 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
IllegalArgumentException if there is already a RecyclerView.OnFlingListener attached to the provided RecyclerView.
IllegalStateException

calculateDistanceToFinalSnap

added in version 25.1.0
int[] calculateDistanceToFinalSnap (RecyclerView.LayoutManager layoutManager, 
                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
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
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 version 25.1.0
int[] calculateScrollDistance (int velocityX, 
                int velocityY)

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

findSnapView

added in version 25.1.0
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
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 version 25.1.0
int findTargetSnapPosition (RecyclerView.LayoutManager layoutManager, 
                int velocityX, 
                int velocityY)

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 version 25.1.0
boolean onFling (int velocityX, 
                int velocityY)

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 RecyclerView.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 methods

createScroller

added in version 26.1.0
RecyclerView.SmoothScroller createScroller (RecyclerView.LayoutManager layoutManager)

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 version 25.1.0
LinearSmoothScroller createSnapScroller (RecyclerView.LayoutManager layoutManager)

This method was deprecated in API level 26.1.0.
use createScroller(LayoutManager) instead.

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.

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