belongs to Maven artifact com.android.support:support-compat:28.0.0-alpha1
NestedScrollingChild
public
interface
NestedScrollingChild
| android.support.v4.view.NestedScrollingChild |
Known Indirect Subclasses
|
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 Android
5.0 Lollipop and newer.
Summary
Public methods | |
|---|---|
abstract
boolean
|
dispatchNestedFling(float velocityX, float velocityY, boolean consumed)
Dispatch a fling to a nested scrolling parent. |
abstract
boolean
|
dispatchNestedPreFling(float velocityX, float velocityY)
Dispatch a fling to a nested scrolling parent before it is processed by this view. |
abstract
boolean
|
dispatchNestedPreScroll(int dx, int dy, int[] consumed, int[] offsetInWindow)
Dispatch one step of a nested scroll in progress before this view consumes any portion of it. |
abstract
boolean
|
dispatchNestedScroll(int dxConsumed, int dyConsumed, int dxUnconsumed, int dyUnconsumed, int[] offsetInWindow)
Dispatch one step of a nested scroll in progress. |
abstract
boolean
|
hasNestedScrollingParent()
Returns true if this view has a nested scrolling parent. |
abstract
boolean
|
isNestedScrollingEnabled()
Returns true if nested scrolling is enabled for this view. |
abstract
void
|
setNestedScrollingEnabled(boolean enabled)
Enable or disable nested scrolling for this view. |
abstract
boolean
|
startNestedScroll(int axes)
Begin a nestable scroll operation along the given axes. |
abstract
void
|
stopNestedScroll()
Stop a nested scroll in progress. |
Public methods
dispatchNestedFling
boolean dispatchNestedFling (float velocityX,
float velocityY,
boolean consumed)Dispatch a fling to a nested scrolling parent.
This method should be used to indicate 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 | |
|---|---|
velocityX |
float: Horizontal fling velocity in pixels per second |
velocityY |
float: Vertical fling velocity in pixels per second |
consumed |
boolean: true if the child consumed the fling, false otherwise |
| Returns | |
|---|---|
boolean |
true if the nested scrolling parent consumed or otherwise reacted to the fling |
dispatchNestedPreFling
boolean dispatchNestedPreFling (float velocityX,
float velocityY)Dispatch a fling to a nested scrolling parent before it is processed by this view.
Nested pre-fling events are to nested fling events what touch intercept is to touch
and what nested pre-scroll is to nested scroll. dispatchNestedPreFling
offsets an opportunity for the parent view in a nested fling to fully consume the fling
before the child view consumes it. If this method returns true, a nested
parent view consumed the fling and this view should not scroll as a result.
For a better user experience, only one view in a nested scrolling chain should consume the fling at a time. If a parent view consumed the fling this method will return false. Custom view implementations should account for this in two ways:
- If a custom view is paged and needs to settle to a fixed page-point, do not
call
dispatchNestedPreFling; consume the fling and settle to a valid position regardless. - If a nested parent does consume the fling, this view should not scroll at all, even to settle back to a valid idle position.
Views should also not offer fling velocities to nested parent views along an axis
where scrolling is not currently supported; a ScrollView
should not offer a horizontal fling velocity to its parents since scrolling along that
axis is not permitted and carrying velocity along that motion does not make sense.
| Parameters | |
|---|---|
velocityX |
float: Horizontal fling velocity in pixels per second |
velocityY |
float: Vertical fling velocity in pixels per second |
| Returns | |
|---|---|
boolean |
true if a nested scrolling parent consumed the fling |
dispatchNestedPreScroll
boolean dispatchNestedPreScroll (int dx,
int dy,
int[] consumed,
int[] offsetInWindow)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 | |
|---|---|
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. |
| Returns | |
|---|---|
boolean |
true if the parent consumed some or all of the scroll delta |
dispatchNestedScroll
boolean dispatchNestedScroll (int dxConsumed,
int dyConsumed,
int dxUnconsumed,
int dyUnconsumed,
int[] offsetInWindow)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 | |
|---|---|
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. |
| Returns | |
|---|---|
boolean |
true if the event was dispatched, false if it could not be dispatched. |
hasNestedScrollingParent
boolean hasNestedScrollingParent ()
Returns true if this view has a nested scrolling parent.
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.
| Returns | |
|---|---|
boolean |
whether this view has a nested scrolling parent |
isNestedScrollingEnabled
boolean isNestedScrollingEnabled ()
Returns true if nested scrolling is enabled for this view.
If nested scrolling is enabled and this View class implementation supports it, this view will act as a nested scrolling child view when applicable, forwarding data about the scroll operation in progress to a compatible and cooperating nested scrolling parent.
| Returns | |
|---|---|
boolean |
true if nested scrolling is enabled |
See also:
setNestedScrollingEnabled
void setNestedScrollingEnabled (boolean enabled)
Enable or disable nested scrolling for this view.
If this property is set to true the view will be permitted to initiate nested
scrolling operations with a compatible parent view in the current hierarchy. If this
view does not implement nested scrolling this will have no effect. Disabling nested scrolling
while a nested scroll is in progress has the effect of stopping
the nested scroll.
| Parameters | |
|---|---|
enabled |
boolean: true to enable nested scrolling, false to disable |
See also:
startNestedScroll
boolean startNestedScroll (int axes)
Begin a nestable scroll operation along the given axes.
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 this corresponds to the initial ACTION_DOWN.
In the case of touch scrolling the nested scroll will be terminated automatically in
the same manner as requestDisallowInterceptTouchEvent(boolean).
In the event of programmatic scrolling the caller must explicitly call
stopNestedScroll() 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
onNestedScroll(View, int, int, int, int).
| Parameters | |
|---|---|
axes |
int: Flags consisting of a combination of SCROLL_AXIS_HORIZONTAL
and/or SCROLL_AXIS_VERTICAL. |
| Returns | |
|---|---|
boolean |
true if a cooperative parent was found and nested scrolling has been enabled for the current gesture. |
stopNestedScroll
void stopNestedScroll ()
Stop a nested scroll in progress.
Calling this method when a nested scroll is not currently in progress is harmless.
See also:
Annotations
Interfaces
- ActionProvider.VisibilityListener
- AsyncLayoutInflater.OnInflateFinishedListener
- LayoutInflaterFactory
- MenuItemCompat.OnActionExpandListener
- NestedScrollingChild
- NestedScrollingChild2
- NestedScrollingParent
- NestedScrollingParent2
- OnApplyWindowInsetsListener
- ScrollingView
- TintableBackgroundView
- ViewPager.OnAdapterChangeListener
- ViewPager.OnPageChangeListener
- ViewPager.PageTransformer
- ViewPropertyAnimatorListener
- ViewPropertyAnimatorUpdateListener
Classes
- AbsSavedState
- AccessibilityDelegateCompat
- ActionProvider
- AsyncLayoutInflater
- GestureDetectorCompat
- GravityCompat
- InputDeviceCompat
- LayoutInflaterCompat
- MarginLayoutParamsCompat
- MenuCompat
- MenuItemCompat
- MotionEventCompat
- NestedScrollingChildHelper
- NestedScrollingParentHelper
- PagerAdapter
- PagerTabStrip
- PagerTitleStrip
- PointerIconCompat
- ScaleGestureDetectorCompat
- VelocityTrackerCompat
- ViewCompat
- ViewConfigurationCompat
- ViewGroupCompat
- ViewPager
- ViewPager.LayoutParams
- ViewPager.SavedState
- ViewPager.SimpleOnPageChangeListener
- ViewParentCompat
- ViewPropertyAnimatorCompat
- ViewPropertyAnimatorListenerAdapter
- WindowCompat
- WindowInsetsCompat