NestedScrollingChild2
interface NestedScrollingChild2 : NestedScrollingChild
androidx.core.view.NestedScrollingChild2 |
This interface should be implemented by View
subclasses that wish to support dispatching nested scrolling operations to a cooperating parent ViewGroup
.
Classes implementing this interface should create a final instance of a NestedScrollingChildHelper
as a field and delegate any View methods to the NestedScrollingChildHelper
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 all versions of Android.
Summary
Public methods |
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abstract Boolean |
dispatchNestedPreScroll(dx: Int, dy: Int, @Nullable consumed: IntArray?, @Nullable offsetInWindow: IntArray?, type: Int) Dispatch one step of a nested scroll in progress before this view consumes any portion of it. |
abstract Boolean |
dispatchNestedScroll(dxConsumed: Int, dyConsumed: Int, dxUnconsumed: Int, dyUnconsumed: Int, @Nullable offsetInWindow: IntArray?, type: Int) Dispatch one step of a nested scroll in progress. |
abstract Boolean |
hasNestedScrollingParent(type: Int) Returns true if this view has a nested scrolling parent for the given input type. |
abstract Boolean |
startNestedScroll(axes: Int, type: Int) Begin a nestable scroll operation along the given axes, for the given input type. |
abstract Unit |
stopNestedScroll(type: Int) Stop a nested scroll in progress for the given input type. |
Inherited functions |
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Public methods
dispatchNestedPreScroll
abstract fun dispatchNestedPreScroll(dx: Int, dy: Int, @Nullable consumed: IntArray?, @Nullable offsetInWindow: IntArray?, type: Int): Boolean
Dispatch one step of a nested scroll in progress before this view consumes any portion of it.
Nested pre-scroll events are to nested scroll events what touch intercept is to touch. dispatchNestedPreScroll
offers an opportunity for the parent view in a nested scrolling operation to consume some or all of the scroll operation before the child view consumes it.
Parameters | |
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dx |
Int: Horizontal scroll distance in pixels |
dy |
Int: Vertical scroll distance in pixels |
consumed |
Int: Output. If not null, consumed[0] will contain the consumed component of dx and consumed[1] the consumed dy. |
offsetInWindow |
Int: Optional. If not null, on return this will contain the offset in local view coordinates of this view from before this operation to after it completes. View implementations may use this to adjust expected input coordinate tracking. |
type |
Int: the type of input which cause this scroll event |
Return | |
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Boolean: true if the parent consumed some or all of the scroll delta |
dispatchNestedScroll
abstract fun dispatchNestedScroll(dxConsumed: Int, dyConsumed: Int, dxUnconsumed: Int, dyUnconsumed: Int, @Nullable offsetInWindow: IntArray?, type: Int): Boolean
Dispatch one step of a nested scroll in progress.
Implementations of views that support nested scrolling should call this to report info about a scroll in progress to the current nested scrolling parent. If a nested scroll is not currently in progress or nested scrolling is not enabled
for this view this method does nothing.
Compatible View implementations should also call dispatchNestedPreScroll
before consuming a component of the scroll event themselves.
Parameters | |
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dxConsumed |
Int: Horizontal distance in pixels consumed by this view during this scroll step |
dyConsumed |
Int: Vertical distance in pixels consumed by this view during this scroll step |
dxUnconsumed |
Int: Horizontal scroll distance in pixels not consumed by this view |
dyUnconsumed |
Int: Horizontal scroll distance in pixels not consumed by this view |
offsetInWindow |
Int: Optional. If not null, on return this will contain the offset in local view coordinates of this view from before this operation to after it completes. View implementations may use this to adjust expected input coordinate tracking. |
type |
Int: the type of input which cause this scroll event |
Return | |
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Boolean: true if the event was dispatched, false if it could not be dispatched. |
hasNestedScrollingParent
abstract fun hasNestedScrollingParent(type: Int): Boolean
Returns true if this view has a nested scrolling parent for the given input type.
The presence of a nested scrolling parent indicates that this view has initiated a nested scroll and it was accepted by an ancestor view further up the view hierarchy.
Parameters | |
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type |
Int: the type of input which cause this scroll event |
Return | |
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Boolean: whether this view has a nested scrolling parent |
startNestedScroll
abstract fun startNestedScroll(axes: Int, type: Int): Boolean
Begin a nestable scroll operation along the given axes, for the given input type.
A view starting a nested scroll promises to abide by the following contract:
The view will call startNestedScroll upon initiating a scroll operation. In the case of a touch scroll type this corresponds to the initial MotionEvent#ACTION_DOWN
. In the case of touch scrolling the nested scroll will be terminated automatically in the same manner as ViewParent#requestDisallowInterceptTouchEvent(boolean)
. In the event of programmatic scrolling the caller must explicitly call stopNestedScroll(int)
to indicate the end of the nested scroll.
If startNestedScroll
returns true, a cooperative parent was found. If it returns false the caller may ignore the rest of this contract until the next scroll. Calling startNestedScroll while a nested scroll is already in progress will return true.
At each incremental step of the scroll the caller should invoke dispatchNestedPreScroll
once it has calculated the requested scrolling delta. If it returns true the nested scrolling parent at least partially consumed the scroll and the caller should adjust the amount it scrolls by.
After applying the remainder of the scroll delta the caller should invoke dispatchNestedScroll
, passing both the delta consumed and the delta unconsumed. A nested scrolling parent may treat these values differently. See NestedScrollingParent2#onNestedScroll(View, int, int, int, int, int)
.
Parameters | |
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axes |
Int: Flags consisting of a combination of ViewCompat#SCROLL_AXIS_HORIZONTAL and/or ViewCompat#SCROLL_AXIS_VERTICAL . |
type |
Int: the type of input which cause this scroll event |
Return | |
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Boolean: true if a cooperative parent was found and nested scrolling has been enabled for the current gesture. |