NestedScrollingParent

interface NestedScrollingParent
androidx.core.view.NestedScrollingParent

This interface should be implemented by ViewGroup subclasses that wish to support scrolling operations delegated by a nested child view.

Classes implementing this interface should create a final instance of a NestedScrollingParentHelper as a field and delegate any View or ViewGroup methods to the NestedScrollingParentHelper methods of the same signature.

Views invoking nested scrolling functionality should always do so from the relevant ViewCompat, ViewGroupCompat or ViewParentCompat compatibility shim static methods. This ensures interoperability with nested scrolling views on Android 5.0 Lollipop and newer.

Summary

Public methods
abstract Int

Return the current axes of nested scrolling for this NestedScrollingParent.

abstract Boolean
onNestedFling(@NonNull target: View, velocityX: Float, velocityY: Float, consumed: Boolean)

Request a fling from a nested scroll.

abstract Boolean
onNestedPreFling(@NonNull target: View, velocityX: Float, velocityY: Float)

React to a nested fling before the target view consumes it.

abstract Unit
onNestedPreScroll(@NonNull target: View, dx: Int, dy: Int, @NonNull consumed: IntArray)

React to a nested scroll in progress before the target view consumes a portion of the scroll.

abstract Unit
onNestedScroll(@NonNull target: View, dxConsumed: Int, dyConsumed: Int, dxUnconsumed: Int, dyUnconsumed: Int)

React to a nested scroll in progress.

abstract Unit
onNestedScrollAccepted(@NonNull child: View, @NonNull target: View, axes: Int)

React to the successful claiming of a nested scroll operation.

abstract Boolean
onStartNestedScroll(@NonNull child: View, @NonNull target: View, axes: Int)

React to a descendant view initiating a nestable scroll operation, claiming the nested scroll operation if appropriate.

abstract Unit
onStopNestedScroll(@NonNull target: View)

React to a nested scroll operation ending.

Public methods

getNestedScrollAxes

abstract fun getNestedScrollAxes(): Int

Return the current axes of nested scrolling for this NestedScrollingParent.

A NestedScrollingParent returning something other than ViewCompat#SCROLL_AXIS_NONE is currently acting as a nested scrolling parent for one or more descendant views in the hierarchy.

Return
Int: Flags indicating the current axes of nested scrolling

onNestedFling

abstract fun onNestedFling(@NonNull target: View, velocityX: Float, velocityY: Float, consumed: Boolean): Boolean

Request a fling from a nested scroll.

This method signifies that a nested scrolling child has detected suitable conditions for a fling. Generally this means that a touch scroll has ended with a velocity in the direction of scrolling that meets or exceeds the minimum fling velocity along a scrollable axis.

If a nested scrolling child view would normally fling but it is at the edge of its own content, it can use this method to delegate the fling to its nested scrolling parent instead. The parent may optionally consume the fling or observe a child fling.

Parameters
target View: View that initiated the nested scroll
velocityX View: Horizontal velocity in pixels per second
velocityY View: Vertical velocity in pixels per second
consumed View: true if the child consumed the fling, false otherwise
Return
Boolean: true if this parent consumed or otherwise reacted to the fling

onNestedPreFling

abstract fun onNestedPreFling(@NonNull target: View, velocityX: Float, velocityY: Float): Boolean

React to a nested fling before the target view consumes it.

This method siginfies that a nested scrolling child has detected a fling with the given velocity along each axis. Generally this means that a touch scroll has ended with a velocity in the direction of scrolling that meets or exceeds the minimum fling velocity along a scrollable axis.

If a nested scrolling parent is consuming motion as part of a pre-scroll, it may be appropriate for it to also consume the pre-fling to complete that same motion. By returning true from this method, the parent indicates that the child should not fling its own internal content as well.

Parameters
target View: View that initiated the nested scroll
velocityX View: Horizontal velocity in pixels per second
velocityY View: Vertical velocity in pixels per second
Return
Boolean: true if this parent consumed the fling ahead of the target view

onNestedPreScroll

abstract fun onNestedPreScroll(@NonNull target: View, dx: Int, dy: Int, @NonNull consumed: IntArray): Unit

React to a nested scroll in progress before the target view consumes a portion of the scroll.

When working with nested scrolling often the parent view may want an opportunity to consume the scroll before the nested scrolling child does. An example of this is a drawer that contains a scrollable list. The user will want to be able to scroll the list fully into view before the list itself begins scrolling.

onNestedPreScroll is called when a nested scrolling child invokes View#dispatchNestedPreScroll(int, int, int[], int[]). The implementation should report how any pixels of the scroll reported by dx, dy were consumed in the consumed array. Index 0 corresponds to dx and index 1 corresponds to dy. This parameter will never be null. Initial values for consumed[0] and consumed[1] will always be 0.

Parameters
target View: View that initiated the nested scroll
dx View: Horizontal scroll distance in pixels
dy View: Vertical scroll distance in pixels
consumed View: Output. The horizontal and vertical scroll distance consumed by this parent

onNestedScroll

abstract fun onNestedScroll(@NonNull target: View, dxConsumed: Int, dyConsumed: Int, dxUnconsumed: Int, dyUnconsumed: Int): Unit

React to a nested scroll in progress.

This method will be called when the ViewParent's current nested scrolling child view dispatches a nested scroll event. To receive calls to this method the ViewParent must have previously returned true for a call to onStartNestedScroll(View, View, int).

Both the consumed and unconsumed portions of the scroll distance are reported to the ViewParent. An implementation may choose to use the consumed portion to match or chase scroll position of multiple child elements, for example. The unconsumed portion may be used to allow continuous dragging of multiple scrolling or draggable elements, such as scrolling a list within a vertical drawer where the drawer begins dragging once the edge of inner scrolling content is reached.

Parameters
target View: The descendent view controlling the nested scroll
dxConsumed View: Horizontal scroll distance in pixels already consumed by target
dyConsumed View: Vertical scroll distance in pixels already consumed by target
dxUnconsumed View: Horizontal scroll distance in pixels not consumed by target
dyUnconsumed View: Vertical scroll distance in pixels not consumed by target

onNestedScrollAccepted

abstract fun onNestedScrollAccepted(@NonNull child: View, @NonNull target: View, axes: Int): Unit

React to the successful claiming of a nested scroll operation.

This method will be called after onStartNestedScroll returns true. It offers an opportunity for the view and its superclasses to perform initial configuration for the nested scroll. Implementations of this method should always call their superclass's implementation of this method if one is present.

Parameters
child View: Direct child of this ViewParent containing target
target View: View that initiated the nested scroll
axes View: Flags consisting of ViewCompat#SCROLL_AXIS_HORIZONTAL, ViewCompat#SCROLL_AXIS_VERTICAL or both

onStartNestedScroll

abstract fun onStartNestedScroll(@NonNull child: View, @NonNull target: View, axes: Int): Boolean

React to a descendant view initiating a nestable scroll operation, claiming the nested scroll operation if appropriate.

This method will be called in response to a descendant view invoking ViewCompat#startNestedScroll(View, int). Each parent up the view hierarchy will be given an opportunity to respond and claim the nested scrolling operation by returning true.

This method may be overridden by ViewParent implementations to indicate when the view is willing to support a nested scrolling operation that is about to begin. If it returns true, this ViewParent will become the target view's nested scrolling parent for the duration of the scroll operation in progress. When the nested scroll is finished this ViewParent will receive a call to onStopNestedScroll(View).

Parameters
child View: Direct child of this ViewParent containing target
target View: View that initiated the nested scroll
axes View: Flags consisting of ViewCompat#SCROLL_AXIS_HORIZONTAL, ViewCompat#SCROLL_AXIS_VERTICAL or both
Return
Boolean: true if this ViewParent accepts the nested scroll operation

onStopNestedScroll

abstract fun onStopNestedScroll(@NonNull target: View): Unit

React to a nested scroll operation ending.

Perform cleanup after a nested scrolling operation. This method will be called when a nested scroll stops, for example when a nested touch scroll ends with a MotionEvent#ACTION_UP or MotionEvent#ACTION_CANCEL event. Implementations of this method should always call their superclass's implementation of this method if one is present.

Parameters
target View: View that initiated the nested scroll