.
java.lang.Object | |||
↳ | android.view.View | ||
↳ | android.view.ViewGroup | ||
↳ | android.support.v7.widget.RecyclerView |
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HorizontalGridView, VerticalGridView
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这个灵活可变的View组件提供了一个在有限的窗口界面显示一个大数据集.
RecyclerView.Adapter
的子类,负责提供用于展示数据集中某条目数据的View组件.getChildAt(int)
方法中使用. 与Position形成对比.RecyclerView 引入了一个附加的抽象层次在RecyclerView.Adapter
和RecyclerView.LayoutManager
之间,用于在布局计算时成批量地观察数据集的变化. 这样从追踪Adapter(适配器)数据变化到计算动画效果, 产生一个布局管理器(LayoutManager).它同样对提升性能很有帮助,因为所有的组件绑定发生的同事时,避免没有数据改变的组件重新绑定数据.
鉴于上述原因, 在 RecycleView 中有两种类型的与Position相关的方法:
这两个位置 (Position) 基本上是一样的, 除了在分发 adapter.notify*
事件 和 计算更新的布局的时候不一样.
返回或者接收 布局位置(*LayoutPosition*
) 的方法, 使用的位置是截止到最近的布局计算的位置 (例如 getLayoutPosition()
,findViewHolderForLayoutPosition(int)
). 这些位置会一直变化, 直到最近的布局计算完成. 你可以依赖这些位置, 这些位置与用户当前在屏幕上看到的位置是一致的.例如, 如果你在屏幕上有一个项目列表, 用户要求使用第五个项目元素, 你可以使用这些方法, 因为这些方法对应的位置就是用户看到的位置.
另外一些关于 适配器位置(*AdapterPosition*
)的方法 (例如: getAdapterPosition()
, findViewHolderForAdapterPosition(int)
), 当你需要去使用最新的适配器位置时, 你应在使用这些方法, 即使这些位置还没有针对对布局进行更新. 例如, 如果你触发了 ViewHolder 点击事件, 想要去获取适配器中的项目元素, 你应该使用 getAdapterPosition()
方法. 注意这些方法可能不能去计算适配器的位置, 如果在 notifyDataSetChanged()
方法被调用, 同时新的布局在没有被计算时. 鉴于以上原因, 你应该小心的去处理 方法返回 NO_POSITION
或者 null
结果的情况.
当你在重写布局管理器 RecyclerView.LayoutManager
时, 你总是想要去获取布局位置(Layout Position), 当你在重写 适配器 RecyclerView.Adapter
, 时, 你总是要获取适配器位置 (adapter positions).
class | RecyclerView.Adapter |
适配器基类 |
适配器提供了一个功能, 可以绑定应用相关的数据集 与展示在 RecycleView 中的项目元素的 View 组件. | ||
class | RecyclerView.AdapterDataObserver | 观察 适配器 (RecycleView.Adapter) 变化的 观察者基类. |
interface | RecyclerView.ChildDrawingOrderCallback | 改变 RecycleView 子组件的 绘制顺序的回调接口. |
class | RecyclerView.ItemAnimator | 该类定义了条目发生改变时 适配器 的动画效果. |
class | RecyclerView.ItemDecoration | 项目装饰, 在适配器数据集中指定的项目显示组件上, 添加一个特别的图画 和 布局. |
class | RecyclerView.LayoutManager | 布局管理器 (LayoutManager) 主要负责在 RecycleView 中测量和放置项目 View 组件, 同时决定当项目 View 组件对用户不可见时回收 项目 View 组件的方案策略; |
class | RecyclerView.LayoutParams | LayoutParams 的子类, 用于设置 RecycleView 子组件. |
interface | RecyclerView.OnChildAttachStateChangeListener | 如果将该监听器接口对象设置给 RecycleView 后, 当 ViewHolder 从 RecycleView 中被附加或者移除的时候该监听器就会被通知. |
interface | RecyclerView.OnItemTouchListener | 项目触摸监听器的作用 : RecycleView 的层级中触摸事件被当做 RecycleView 自己的滚动操作, 设置了该监听器, 就可以在 RecycleView 将触摸事件当做滚动事件之前拦截这些触摸操作. |
class | RecyclerView.OnScrollListener | 滚动监听器 (OnScrollListener) 被设置给 RecycleView 后, 当滚动事件被触发时, 可以接收滚动相关的信息. |
class | RecyclerView.RecycledViewPool | RecycleView 池 可以让你在不同的 RecycleView 之间 分享 View 组件. |
class | RecyclerView.Recycler | Recycler (复用器) 作用是管理 已销毁 或者 被分离的 项目组件 以用于复用. |
interface | RecyclerView.RecyclerListener | 循环复用监听器 : 设置给 RecycleView 后, 当 View 组件被复用时, 会接收于此相关的信息. |
class | RecyclerView.SimpleOnItemTouchListener | RecycleView.OnItemTouchListener 接口的实现类, 有一个空的方法体 和 默认返回值. |
class | RecyclerView.SmoothScroller | 平滑滚动类的基类 |
class | RecyclerView.State | 包含了一些 关于当前的 RecycleView 的状态 的有用的信息, 如 目标滚动位置 和 View 组件 的焦点. |
class | RecyclerView.ViewCacheExtension | ViewCacheExtension 是一个帮助类, 用于提供一个 可以被开发者 操纵的 View 缓存附加层. |
class | RecyclerView.ViewHolder | 一个 ViewHolder 描述了一个条目组件 (View) 和要在 RecycleView 中的该位置显示的元数据(metadata). |
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Inherited XML Attributes
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XML Attributes | |||||||||||
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Attribute Name | Related Method | Description | |||||||||
android.support.v7.recyclerview:layoutManager | RecycleView 的布局管理器 |
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Inherited Fields
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Inherited Constants
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Public Constructors | |||||||||||
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RecyclerView( Context context) | |||||||||||
RecyclerView( Context context, AttributeSet attrs) | |||||||||||
RecyclerView( Context context, AttributeSet attrs, int defStyle) |
Public Methods | |||||||||||
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void | addFocusables( ArrayList< View> views, int direction, int focusableMode)
添加任意可获取焦点的组件, 这些被添加的组件是该 View (调用本方法的 View 组件, 可能包括这个 View 本身也可以获取焦点) 的子节点.
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void | addItemDecoration( RecyclerView.ItemDecoration decor)
为这个 RecycleView 添加一个项目装饰 (RecycleView.ItemDecoration).
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void | addItemDecoration( RecyclerView.ItemDecoration decor, int index)
为这个 RecycleView 添加一个项目装饰 (RecycleView.ItemDecoration).
|
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void | addOnChildAttachStateChangeListener( RecyclerView.OnChildAttachStateChangeListener listener)
注册一个监听器, 当子组件被附加或者从 RecycleView 中移除时, 会得到一个相关的通知.
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void | addOnItemTouchListener( RecyclerView.OnItemTouchListener listener)
添加一个项目触摸监听器用于监听触摸事件, 在这些事件被传给子组件 或者 在 RecycleView 级别上被 当做滚动事件 前, 拦截这些事件.
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void | addOnScrollListener( RecyclerView.OnScrollListener listener)
添加一个监听器, 作用是当滚动状态 或者 位置发生变化时得到相应的通知.
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void | clearOnChildAttachStateChangeListeners()
移除 通过 addOnChildAttachStateChangeListener 方法添加的监听器.
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void | clearOnScrollListeners()
之前 设置的 关于通知任意滚动状态 或 位置 变化的 监听器, 该方法用于移除这些次要的监听器.
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int | computeHorizontalScrollExtent()
在水平范围中, 计算水平滚动条的水平范围. |
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int | computeHorizontalScrollOffset()
在水平范围中, 计算水平滚动条的水平偏移量. |
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int | computeHorizontalScrollRange()
计算 横向滚动条 在水平方向上的滚动范围. |
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int | computeVerticalScrollExtent()
在垂直范围内, 计算垂直滚动条翻越的范围. |
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int | computeVerticalScrollOffset()
在垂直方向范围中, 计算垂直方向上的 垂直滚动条 的翻越的偏移量. |
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int | computeVerticalScrollRange()
计算垂直滚动条的滚动范围. |
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boolean | dispatchNestedFling(float velocityX, float velocityY, boolean consumed)
分发抛出动作到嵌套的滑动中.
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boolean | dispatchNestedPreFling(float velocityX, float velocityY)
在动作被 View 组件处理前, 分发一个抛出动作到嵌套滑动中.
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boolean | dispatchNestedPreScroll(int dx, int dy, int[] consumed, int[] offsetInWindow)
在 View 执行 滚动动作前, 分发一个嵌套滚动的步骤;
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boolean | dispatchNestedScroll(int dxConsumed, int dyConsumed, int dxUnconsumed, int dyUnconsumed, int[] offsetInWindow)
分发一个嵌套滚动中的一个步骤;
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void | draw( Canvas c)
主要用于在给定的画布中 渲染 View 组件 (及 View 组件的子组件) ;
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boolean | drawChild( Canvas canvas, View child, long drawingTime)
绘制 View 组中的一个子组件;
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View | findChildViewUnder(float x, float y)
在给定的一点找出最顶端的 View 组件;
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RecyclerView.ViewHolder | findViewHolderForAdapterPosition(int position)
在数据集中, 通过给定的 位置, 找出 item 条目的 ViewHolder;
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RecyclerView.ViewHolder | findViewHolderForItemId(long id)
根据一个给定 item 的 id 编号找出其 ViewHolder;
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RecyclerView.ViewHolder | findViewHolderForLayoutPosition(int position)
根据给定的 最新 使用的布局 的位置 (也是数据集的位置) 返回对应的 item 条目的 ViewHolder;
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RecyclerView.ViewHolder | findViewHolderForPosition(int position)
该方法弃用, 使用 findViewHolderForLayoutPosition(int) orfindViewHolderForAdapterPosition(int)
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boolean | fling(int velocityX, int velocityY)
给定一个初始的速度 (像素/秒) 沿着 对应的坐标轴 开始一个标准的抛出动作;
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View | focusSearch( View focused, int direction)
在给定的方向上, 找出最近的 View 组件, 获取焦点;
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ViewGroup.LayoutParams | generateLayoutParams( AttributeSet attrs)
Returns a new set of layout parameters based on the supplied attributes set.
基于给定的属性集合, 返回一个新的布局参数;
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Adapter | getAdapter()
Retrieves the previously set adapter or null if no adapter is set.
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int | getBaseline()
Return the offset of the RecyclerView's text baseline from the its top boundary. |
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int | getChildAdapterPosition( View child)
Return the adapter position that the given child view corresponds to.
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long | getChildItemId( View child)
Return the stable item id that the given child view corresponds to.
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int | getChildLayoutPosition( View child)
Return the adapter position of the given child view as of the latest completed layout pass.
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int | getChildPosition( View child)
This method is deprecated. use getChildAdapterPosition(View) or getChildLayoutPosition(View) .
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RecyclerView.ViewHolder | getChildViewHolder( View child)
Retrieve the
RecyclerView.ViewHolder for the given child view.
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RecyclerViewAccessibilityDelegate | getCompatAccessibilityDelegate()
Returns the accessibility delegate compatibility implementation used by the RecyclerView.
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RecyclerView.ItemAnimator | getItemAnimator()
Gets the current ItemAnimator for this RecyclerView.
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RecyclerView.LayoutManager | getLayoutManager()
Return the
RecyclerView.LayoutManager currently responsible for layout policy for this RecyclerView.
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int | getMaxFlingVelocity()
Returns the maximum fling velocity used by this RecyclerView.
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int | getMinFlingVelocity()
Returns the minimum velocity to start a fling.
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RecyclerView.RecycledViewPool | getRecycledViewPool()
Retrieve this RecyclerView's
RecyclerView.RecycledViewPool .
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int | getScrollState()
Return the current scrolling state of the RecyclerView.
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boolean | hasFixedSize() | ||||||||||
boolean | hasNestedScrollingParent()
Returns true if this view has a nested scrolling parent.
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boolean | hasPendingAdapterUpdates()
Returns whether there are pending adapter updates which are not yet applied to the layout.
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void | invalidateItemDecorations()
Invalidates all ItemDecorations.
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boolean | isAnimating()
Returns true if RecyclerView is currently running some animations.
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boolean | isAttachedToWindow()
Returns true if RecyclerView is attached to window.
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boolean | isComputingLayout()
Returns whether RecyclerView is currently computing a layout.
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boolean | isLayoutFrozen()
Returns true if layout and scroll are frozen.
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boolean | isNestedScrollingEnabled()
Returns true if nested scrolling is enabled for this view.
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void | offsetChildrenHorizontal(int dx)
Offset the bounds of all child views by
dx pixels.
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void | offsetChildrenVertical(int dy)
Offset the bounds of all child views by
dy pixels.
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void | onChildAttachedToWindow( View child)
Called when an item view is attached to this RecyclerView.
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void | onChildDetachedFromWindow( View child)
Called when an item view is detached from this RecyclerView.
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void | onDraw( Canvas c)
Implement this to do your drawing.
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boolean | onGenericMotionEvent( MotionEvent event)
Implement this method to handle generic motion events.
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boolean | onInterceptTouchEvent( MotionEvent e)
Implement this method to intercept all touch screen motion events.
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void | onScrollStateChanged(int state)
Called when the scroll state of this RecyclerView changes.
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void | onScrolled(int dx, int dy)
Called when the scroll position of this RecyclerView changes.
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boolean | onTouchEvent( MotionEvent e)
Implement this method to handle touch screen motion events.
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void | removeItemDecoration( RecyclerView.ItemDecoration decor)
Remove an
RecyclerView.ItemDecoration from this RecyclerView.
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void | removeOnChildAttachStateChangeListener( RecyclerView.OnChildAttachStateChangeListener listener)
Removes the provided listener from child attached state listeners list.
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void | removeOnItemTouchListener( RecyclerView.OnItemTouchListener listener)
Remove an
RecyclerView.OnItemTouchListener .
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void | removeOnScrollListener( RecyclerView.OnScrollListener listener)
Remove a listener that was notified of any changes in scroll state or position.
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void | requestChildFocus( View child, View focused)
Called when a child of this parent wants focus
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boolean | requestChildRectangleOnScreen( View child, Rect rect, boolean immediate)
Called when a child of this group wants a particular rectangle to be positioned onto the screen.
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void | requestDisallowInterceptTouchEvent(boolean disallowIntercept)
Called when a child does not want this parent and its ancestors to intercept touch events with
onInterceptTouchEvent(MotionEvent) .
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void | requestLayout()
Call this when something has changed which has invalidated the layout of this view.
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void | scrollBy(int x, int y)
Move the scrolled position of your view.
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void | scrollTo(int x, int y)
Set the scrolled position of your view.
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void | scrollToPosition(int position)
Convenience method to scroll to a certain position.
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void | sendAccessibilityEventUnchecked( AccessibilityEvent event)
This method behaves exactly as
sendAccessibilityEvent(int) but takes as an argument an empty
AccessibilityEvent and does not perform a check whether accessibility is enabled.
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void | setAccessibilityDelegateCompat( RecyclerViewAccessibilityDelegate accessibilityDelegate)
Sets the accessibility delegate compatibility implementation used by RecyclerView.
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void | setAdapter( Adapter adapter)
Set a new adapter to provide child views on demand.
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void | setChildDrawingOrderCallback( RecyclerView.ChildDrawingOrderCallback childDrawingOrderCallback)
Sets the
RecyclerView.ChildDrawingOrderCallback to be used for drawing children.
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void | setClipToPadding(boolean clipToPadding)
Sets whether this ViewGroup will clip its children to its padding and resize (but not clip) any EdgeEffect to the padded region, if padding is present.
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void | setHasFixedSize(boolean hasFixedSize)
RecyclerView can perform several optimizations if it can know in advance that changes in adapter content cannot change the size of the RecyclerView itself.
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void | setItemAnimator( RecyclerView.ItemAnimator animator)
Sets the
RecyclerView.ItemAnimator that will handle animations involving changes to the items in this RecyclerView.
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void | setItemViewCacheSize(int size)
Set the number of offscreen views to retain before adding them to the potentially shared
recycled view pool .
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void | setLayoutFrozen(boolean frozen)
Enable or disable layout and scroll.
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void | setLayoutManager( RecyclerView.LayoutManager layout)
Set the
RecyclerView.LayoutManager that this RecyclerView will use.
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void | setNestedScrollingEnabled(boolean enabled)
Enable or disable nested scrolling for this view.
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void | setOnScrollListener( RecyclerView.OnScrollListener listener)
This method is deprecated. Use addOnScrollListener(OnScrollListener) andremoveOnScrollListener(OnScrollListener)
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void | setRecycledViewPool( RecyclerView.RecycledViewPool pool)
Recycled view pools allow multiple RecyclerViews to share a common pool of scrap views.
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void | setRecyclerListener( RecyclerView.RecyclerListener listener)
Register a listener that will be notified whenever a child view is recycled.
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void | setScrollingTouchSlop(int slopConstant)
Configure the scrolling touch slop for a specific use case.
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void | setViewCacheExtension( RecyclerView.ViewCacheExtension extension)
Sets a new
RecyclerView.ViewCacheExtension to be used by the Recycler.
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void | smoothScrollBy(int dx, int dy)
Animate a scroll by the given amount of pixels along either axis.
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void | smoothScrollToPosition(int position)
Starts a smooth scroll to an adapter position.
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boolean | startNestedScroll(int axes)
Begin a nestable scroll operation along the given axes.
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void | stopNestedScroll()
Stop a nested scroll in progress.
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void | stopScroll()
Stop any current scroll in progress, such as one started by
smoothScrollBy(int, int) ,
fling(int, int) or a touch-initiated fling.
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void | swapAdapter( Adapter adapter, boolean removeAndRecycleExistingViews)
Swaps the current adapter with the provided one.
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Protected Methods | |||||||||||
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boolean | checkLayoutParams( ViewGroup.LayoutParams p) | ||||||||||
void | dispatchRestoreInstanceState( SparseArray< Parcelable> container)
Override to prevent thawing of any views created by the adapter.
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void | dispatchSaveInstanceState( SparseArray< Parcelable> container)
Override to prevent freezing of any views created by the adapter.
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ViewGroup.LayoutParams | generateDefaultLayoutParams()
Returns a set of default layout parameters.
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ViewGroup.LayoutParams | generateLayoutParams( ViewGroup.LayoutParams p)
Returns a safe set of layout parameters based on the supplied layout params.
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int | getChildDrawingOrder(int childCount, int i)
Returns the index of the child to draw for this iteration.
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void | onAttachedToWindow()
This is called when the view is attached to a window.
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void | onDetachedFromWindow()
This is called when the view is detached from a window.
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void | onLayout(boolean changed, int l, int t, int r, int b)
Called from layout when this view should assign a size and position to each of its children.
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void | onMeasure(int widthSpec, int heightSpec)
Measure the view and its content to determine the measured width and the measured height. |
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void | onRestoreInstanceState( Parcelable state)
Hook allowing a view to re-apply a representation of its internal state that had previously been generated by
onSaveInstanceState() .
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Parcelable | onSaveInstanceState()
Hook allowing a view to generate a representation of its internal state that can later be used to create a new instance with that same state.
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void | onSizeChanged(int w, int h, int oldw, int oldh)
This is called during layout when the size of this view has changed.
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void | removeDetachedView( View child, boolean animate)
Finishes the removal of a detached view.
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Inherited Methods
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Class name of the Layout Manager to be used.
The class must extend android.support.v7.widget.RecyclerView$LayoutManager and have either a default constructor or constructor with the signature (android.content.Context, android.util.AttributeSet, int, int).
If the name starts with a '.', application package is prefixed. Else, if the name contains a '.', the classname is assumed to be a full class name. Else, the recycler view package name (android.support.v7.widget) is prefixed.
Must be a string value, using '\\;' to escape characters such as '\\n' or '\\uxxxx' for a unicode character.
This may also be a reference to a resource (in the form "@[package:]type:name
") or theme attribute (in the form "?[package:][type:]name
") containing a value of this type.
This is a private symbol.
The RecyclerView is currently being dragged by outside input such as user touch input.
getScrollState()
The RecyclerView is not currently scrolling.
getScrollState()
The RecyclerView is currently animating to a final position while not under outside control.
getScrollState()
Constant for use with setScrollingTouchSlop(int)
. Indicates that the RecyclerView should use the standard touch slop for smooth, continuous scrolling.
Constant for use with setScrollingTouchSlop(int)
. Indicates that the RecyclerView should use the standard touch slop for scrolling widgets that snap to a page or other coarse-grained barrier.
Adds any focusable views that are descendants of this view (possibly including this view if it is focusable itself) to views. This method adds all focusable views regardless if we are in touch mode or only views focusable in touch mode if we are in touch mode or only views that can take accessibility focus if accessibility is enabled depending on the focusable mode parameter.
views | Focusable views found so far or null if all we are interested is the number of focusables. |
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direction | The direction of the focus. |
focusableMode | The type of focusables to be added. |
Add an RecyclerView.ItemDecoration
to this RecyclerView. Item decorations can affect both measurement and drawing of individual item views.
Item decorations are ordered. Decorations placed earlier in the list will be run/queried/drawn first for their effects on item views. Padding added to views will be nested; a padding added by an earlier decoration will mean further item decorations in the list will be asked to draw/pad within the previous decoration's given area.
decor | Decoration to add |
---|
Add an RecyclerView.ItemDecoration
to this RecyclerView. Item decorations can affect both measurement and drawing of individual item views.
Item decorations are ordered. Decorations placed earlier in the list will be run/queried/drawn first for their effects on item views. Padding added to views will be nested; a padding added by an earlier decoration will mean further item decorations in the list will be asked to draw/pad within the previous decoration's given area.
decor | Decoration to add |
---|---|
index | Position in the decoration chain to insert this decoration at. If this value is negative the decoration will be added at the end. |
Register a listener that will be notified whenever a child view is attached to or detached from RecyclerView.
This listener will be called when a LayoutManager or the RecyclerView decides that a child view is no longer needed. If an application associates expensive or heavyweight data with item views, this may be a good place to release or free those resources.
listener | Listener to register |
---|
Add an RecyclerView.OnItemTouchListener
to intercept touch events before they are dispatched to child views or this view's standard scrolling behavior.
Client code may use listeners to implement item manipulation behavior. Once a listener returns true from onInterceptTouchEvent(RecyclerView, MotionEvent)
itsonTouchEvent(RecyclerView, MotionEvent)
method will be called for each incoming MotionEvent until the end of the gesture.
listener | Listener to add |
---|
RecyclerView.SimpleOnItemTouchListener
Add a listener that will be notified of any changes in scroll state or position.
Components that add a listener should take care to remove it when finished. Other components that take ownership of a view may call clearOnScrollListeners()
to remove all attached listeners.
listener | listener to set or null to clear |
---|
Removes all listeners that were added via addOnChildAttachStateChangeListener(OnChildAttachStateChangeListener)
.
Remove all secondary listener that were notified of any changes in scroll state or position.
Compute the horizontal extent of the horizontal scrollbar's thumb within the horizontal range. This value is used to compute the length of the thumb within the scrollbar's track.
The range is expressed in arbitrary units that must be the same as the units used by computeHorizontalScrollRange()
and computeHorizontalScrollOffset()
.
Default implementation returns 0.
If you want to support scroll bars, override computeHorizontalScrollExtent(RecyclerView.State)
in your LayoutManager.
computeHorizontalScrollExtent(RecyclerView.State)
Compute the horizontal offset of the horizontal scrollbar's thumb within the horizontal range. This value is used to compute the length of the thumb within the scrollbar's track.
The range is expressed in arbitrary units that must be the same as the units used by computeHorizontalScrollRange()
and computeHorizontalScrollExtent()
.
Default implementation returns 0.
If you want to support scroll bars, override computeHorizontalScrollOffset(RecyclerView.State)
in your LayoutManager.
(RecyclerView.Adapter)
Compute the horizontal range that the horizontal scrollbar represents.
The range is expressed in arbitrary units that must be the same as the units used by computeHorizontalScrollExtent()
and computeHorizontalScrollOffset()
.
Default implementation returns 0.
If you want to support scroll bars, override computeHorizontalScrollRange(RecyclerView.State)
in your LayoutManager.
computeHorizontalScrollRange(RecyclerView.State)
Compute the vertical extent of the vertical scrollbar's thumb within the vertical range. This value is used to compute the length of the thumb within the scrollbar's track.
The range is expressed in arbitrary units that must be the same as the units used by computeVerticalScrollRange()
and computeVerticalScrollOffset()
.
Default implementation returns 0.
If you want to support scroll bars, override computeVerticalScrollExtent(RecyclerView.State)
in your LayoutManager.
computeVerticalScrollExtent(RecyclerView.State)
Compute the vertical offset of the vertical scrollbar's thumb within the vertical range. This value is used to compute the length of the thumb within the scrollbar's track.
The range is expressed in arbitrary units that must be the same as the units used by computeVerticalScrollRange()
and computeVerticalScrollExtent()
.
Default implementation returns 0.
If you want to support scroll bars, override computeVerticalScrollOffset(RecyclerView.State)
in your LayoutManager.
(RecyclerView.Adapter)
Compute the vertical range that the vertical scrollbar represents.
The range is expressed in arbitrary units that must be the same as the units used by computeVerticalScrollExtent()
and computeVerticalScrollOffset()
.
Default implementation returns 0.
If you want to support scroll bars, override computeVerticalScrollRange(RecyclerView.State)
in your LayoutManager.
computeVerticalScrollRange(RecyclerView.State)
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.
velocityX | Horizontal fling velocity in pixels per second |
---|---|
velocityY | Vertical fling velocity in pixels per second |
consumed | true if the child consumed the fling, false otherwise |
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:
dispatchNestedPreFling
; consume the fling and settle to a valid position regardless.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.
velocityX | Horizontal fling velocity in pixels per second |
---|---|
velocityY | Vertical fling velocity in pixels per second |
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.
dx | Horizontal scroll distance in pixels |
---|---|
dy | Vertical scroll distance in pixels |
consumed | Output. If not null, consumed[0] will contain the consumed component of dx and consumed[1] the consumed dy. |
offsetInWindow | 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. |
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.
dxConsumed | Horizontal distance in pixels consumed by this view during this scroll step |
---|---|
dyConsumed | Vertical distance in pixels consumed by this view during this scroll step |
dxUnconsumed | Horizontal scroll distance in pixels not consumed by this view |
dyUnconsumed | Horizontal scroll distance in pixels not consumed by this view |
offsetInWindow | 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. |
Manually render this view (and all of its children) to the given Canvas. The view must have already done a full layout before this function is called. When implementing a view, implement onDraw(android.graphics.Canvas)
instead of overriding this method. If you do need to override this method, call the superclass version.
c | The Canvas to which the View is rendered. |
---|
Draw one child of this View Group. This method is responsible for getting the canvas in the right state. This includes clipping, translating so that the child's scrolled origin is at 0, 0, and applying any animation transformations.
canvas | The canvas on which to draw the child |
---|---|
child | Who to draw |
drawingTime | The time at which draw is occurring |
Find the topmost view under the given point.
x | Horizontal position in pixels to search |
---|---|
y | Vertical position in pixels to search |
Return the ViewHolder for the item in the given position of the data set. Unlike findViewHolderForLayoutPosition(int)
this method takes into account any pending adapter changes that may not be reflected to the layout yet. On the other hand, if notifyDataSetChanged()
has been called but the new layout has not been calculated yet, this method will return null
since the new positions of views are unknown until the layout is calculated.
This method checks only the children of RecyclerView. If the item at the given position
is not laid out, it will not create a new one.
position | The position of the item in the data set of the adapter |
---|
position
or null if there is no such itemReturn the ViewHolder for the item with the given id. The RecyclerView must use an Adapter with stableIds
to return a non-null value.
This method checks only the children of RecyclerView. If the item with the given id
is not laid out, it will not create a new one.
id | The id for the requested item |
---|
id
or null if there is no such itemReturn the ViewHolder for the item in the given position of the data set as of the latest layout pass.
This method checks only the children of RecyclerView. If the item at the given position
is not laid out, it will not create a new one.
Note that when Adapter contents change, ViewHolder positions are not updated until the next layout calculation. If there are pending adapter updates, the return value of this method may not match your adapter contents. You can use #getAdapterPosition()
to get the current adapter position of a ViewHolder.
position | The position of the item in the data set of the adapter |
---|
position
or null if there is no such itemThis method is deprecated.
use findViewHolderForLayoutPosition(int)
or findViewHolderForAdapterPosition(int)
Begin a standard fling with an initial velocity along each axis in pixels per second. If the velocity given is below the system-defined minimum this method will return false and no fling will occur.
velocityX | Initial horizontal velocity in pixels per second |
---|---|
velocityY | Initial vertical velocity in pixels per second |
canScrollVertically()
canScrollHorizontally()
Find the nearest view in the specified direction that wants to take focus.
focused | The view that currently has focus |
---|---|
direction | One of FOCUS_UP, FOCUS_DOWN, FOCUS_LEFT, and FOCUS_RIGHT, or 0 for not applicable. |
Returns a new set of layout parameters based on the supplied attributes set.
attrs | the attributes to build the layout parameters from |
---|
ViewGroup.LayoutParams
or one of its descendantsRetrieves the previously set adapter or null if no adapter is set.
setAdapter(Adapter)
Return the offset of the RecyclerView's text baseline from the its top boundary. If the LayoutManager of this RecyclerView does not support baseline alignment, this method returns -1.
Return the adapter position that the given child view corresponds to.
child | Child View to query |
---|
NO_POSITION
Return the stable item id that the given child view corresponds to.
child | Child View to query |
---|
NO_ID
Return the adapter position of the given child view as of the latest completed layout pass.
This position may not be equal to Item's adapter position if there are pending changes in the adapter which have not been reflected to the layout yet.
child | Child View to query |
---|
NO_POSITION
if the View is representing a removed item.This method is deprecated.
use getChildAdapterPosition(View)
or getChildLayoutPosition(View)
.
Retrieve the RecyclerView.ViewHolder
for the given child view.
child | Child of this RecyclerView to query for its ViewHolder |
---|
Returns the accessibility delegate compatibility implementation used by the RecyclerView.
Gets the current ItemAnimator for this RecyclerView. A null return value indicates that there is no animator and that item changes will happen without any animations. By default, RecyclerView instantiates and uses an instance of DefaultItemAnimator
.
Return the RecyclerView.LayoutManager
currently responsible for layout policy for this RecyclerView.
Returns the maximum fling velocity used by this RecyclerView.
Returns the minimum velocity to start a fling.
Retrieve this RecyclerView's RecyclerView.RecycledViewPool
. This method will never return null; if no pool is set for this view a new one will be created. SeesetRecycledViewPool
for more information.
setRecycledViewPool(RecycledViewPool)
Return the current scrolling state of the RecyclerView.
SCROLL_STATE_IDLE
, SCROLL_STATE_DRAGGING
or SCROLL_STATE_SETTLING
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 whether there are pending adapter updates which are not yet applied to the layout.
If this method returns true
, it means that what user is currently seeing may not reflect them adapter contents (depending on what has changed). You may use this information to defer or cancel some operations.
This method returns true if RecyclerView has not yet calculated the first layout after it is attached to the Window or the Adapter has been replaced.
Invalidates all ItemDecorations. If RecyclerView has item decorations, calling this method will trigger a requestLayout()
call.
Returns true if RecyclerView is currently running some animations.
If you want to be notified when animations are finished, use isRunning(ItemAnimator.ItemAnimatorFinishedListener)
.
Returns true if RecyclerView is attached to window.
Returns whether RecyclerView is currently computing a layout.
If this method returns true, it means that RecyclerView is in a lockdown state and any attempt to update adapter contents will result in an exception because adapter contents cannot be changed while RecyclerView is trying to compute the layout.
It is very unlikely that your code will be running during this state as it is called by the framework when a layout traversal happens or RecyclerView starts to scroll in response to system events (touch, accessibility etc).
This case may happen if you have some custom logic to change adapter contents in response to a View callback (e.g. focus change callback) which might be triggered during a layout calculation. In these cases, you should just postpone the change using a Handler or a similar mechanism.
true
if RecyclerView is currently computing a layout, false
otherwiseReturns true if layout and scroll are frozen.
setLayoutFrozen(boolean)
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.
Offset the bounds of all child views by dx
pixels. Useful for implementing simple scrolling in LayoutManagers
.
dx | Horizontal pixel offset to apply to the bounds of all child views |
---|
Offset the bounds of all child views by dy
pixels. Useful for implementing simple scrolling in LayoutManagers
.
dy | Vertical pixel offset to apply to the bounds of all child views |
---|
Called when an item view is attached to this RecyclerView.
Subclasses of RecyclerView may want to perform extra bookkeeping or modifications of child views as they become attached. This will be called before aRecyclerView.LayoutManager
measures or lays out the view and is a good time to perform these changes.
child | Child view that is now attached to this RecyclerView and its associated window |
---|
Called when an item view is detached from this RecyclerView.
Subclasses of RecyclerView may want to perform extra bookkeeping or modifications of child views as they become detached. This will be called as aRecyclerView.LayoutManager
fully detaches the child view from the parent and its window.
child | Child view that is now detached from this RecyclerView and its associated window |
---|
Implement this to do your drawing.
c | the canvas on which the background will be drawn |
---|
Implement this method to handle generic motion events.
Generic motion events describe joystick movements, mouse hovers, track pad touches, scroll wheel movements and other input events. The source
of the motion event specifies the class of input that was received. Implementations of this method must examine the bits in the source before processing the event. The following code example shows how this is done.
Generic motion events with source class SOURCE_CLASS_POINTER
are delivered to the view under the pointer. All other generic motion events are delivered to the focused view.
public boolean onGenericMotionEvent(MotionEvent event) { if (event.isFromSource(InputDevice.SOURCE_CLASS_JOYSTICK)) { if (event.getAction() == MotionEvent.ACTION_MOVE) { // process the joystick movement... return true; } } if (event.isFromSource(InputDevice.SOURCE_CLASS_POINTER)) { switch (event.getAction()) { case MotionEvent.ACTION_HOVER_MOVE: // process the mouse hover movement... return true; case MotionEvent.ACTION_SCROLL: // process the scroll wheel movement... return true; } } return super.onGenericMotionEvent(event); }
event | The generic motion event being processed. |
---|
Implement this method to intercept all touch screen motion events. This allows you to watch events as they are dispatched to your children, and take ownership of the current gesture at any point.
Using this function takes some care, as it has a fairly complicated interaction with View.onTouchEvent(MotionEvent)
, and using it requires implementing that method as well as this one in the correct way. Events will be received in the following order:
ACTION_CANCEL
, and all further events will be delivered to your onTouchEvent() method and no longer appear here.e | The motion event being dispatched down the hierarchy. |
---|
Called when the scroll state of this RecyclerView changes. Subclasses should use this method to respond to state changes instead of an explicit listener.
This method will always be invoked before listeners, but after the LayoutManager responds to the scroll state change.
state | the new scroll state, one of SCROLL_STATE_IDLE , SCROLL_STATE_DRAGGING or SCROLL_STATE_SETTLING |
---|
Called when the scroll position of this RecyclerView changes. Subclasses should use this method to respond to scrolling within the adapter's data set instead of an explicit listener.
This method will always be invoked before listeners. If a subclass needs to perform any additional upkeep or bookkeeping after scrolling but before listeners run, this is a good place to do so.
This differs from onScrollChanged(int, int, int, int)
in that it receives the distance scrolled in either direction within the adapter's data set instead of absolute scroll coordinates. Since RecyclerView cannot compute the absolute scroll position from any arbitrary point in the data set, onScrollChanged
will always receive the current getScrollX()
and getScrollY()
values which do not correspond to the data set scroll position. However, some subclasses may choose to use these fields as special offsets.
dx | horizontal distance scrolled in pixels |
---|---|
dy | vertical distance scrolled in pixels |
Implement this method to handle touch screen motion events.
If this method is used to detect click actions, it is recommended that the actions be performed by implementing and calling performClick()
. This will ensure consistent system behavior, including:
ACTION_CLICK
when accessibility features are enablede | The motion event. |
---|
Remove an RecyclerView.ItemDecoration
from this RecyclerView.
The given decoration will no longer impact the measurement and drawing of item views.
decor | Decoration to remove |
---|
addItemDecoration(ItemDecoration)
Removes the provided listener from child attached state listeners list.
listener | Listener to unregister |
---|
Remove an RecyclerView.OnItemTouchListener
. It will no longer be able to intercept touch events.
listener | Listener to remove |
---|
Remove a listener that was notified of any changes in scroll state or position.
listener | listener to set or null to clear |
---|
Called when a child of this parent wants focus
child | The child of this ViewParent that wants focus. This view will contain the focused view. It is not necessarily the view that actually has focus. |
---|---|
focused | The view that is a descendant of child that actually has focus |
Called when a child of this group wants a particular rectangle to be positioned onto the screen. ViewGroup
s overriding this can trust that:
ViewGroup
s overriding this should uphold the contract:
child | The direct child making the request. |
---|---|
rect | The rectangle in the child's coordinates the child wishes to be on the screen. |
immediate | True to forbid animated or delayed scrolling, false otherwise |
Called when a child does not want this parent and its ancestors to intercept touch events with onInterceptTouchEvent(MotionEvent)
.
This parent should pass this call onto its parents. This parent must obey this request for the duration of the touch (that is, only clear the flag after this parent has received an up or a cancel.
disallowIntercept | True if the child does not want the parent to intercept touch events. |
---|
Call this when something has changed which has invalidated the layout of this view. This will schedule a layout pass of the view tree. This should not be called while the view hierarchy is currently in a layout pass (isInLayout()
. If layout is happening, the request may be honored at the end of the current layout pass (and then layout will run again) or after the current frame is drawn and the next layout occurs.
Subclasses which override this method should call the superclass method to handle possible request-during-layout errors correctly.
Move the scrolled position of your view. This will cause a call to onScrollChanged(int, int, int, int)
and the view will be invalidated.
x | the amount of pixels to scroll by horizontally |
---|---|
y | the amount of pixels to scroll by vertically |
Set the scrolled position of your view. This will cause a call to onScrollChanged(int, int, int, int)
and the view will be invalidated.
x | the x position to scroll to |
---|---|
y | the y position to scroll to |
Convenience method to scroll to a certain position. RecyclerView does not implement scrolling logic, rather forwards the call to scrollToPosition(int)
position | Scroll to this adapter position |
---|
scrollToPosition(int)
This method behaves exactly as sendAccessibilityEvent(int)
but takes as an argument an empty AccessibilityEvent
and does not perform a check whether accessibility is enabled.
If an View.AccessibilityDelegate
has been specified via calling setAccessibilityDelegate(AccessibilityDelegate)
itssendAccessibilityEventUnchecked(View, AccessibilityEvent)
is responsible for handling this call.
event | The event to send. |
---|
Sets the accessibility delegate compatibility implementation used by RecyclerView.
accessibilityDelegate | The accessibility delegate to be used by RecyclerView. |
---|
Set a new adapter to provide child views on demand.
When adapter is changed, all existing views are recycled back to the pool. If the pool has only one adapter, it will be cleared.
adapter | The new adapter to set, or null to set no adapter. |
---|
swapAdapter(Adapter, boolean)
Sets the RecyclerView.ChildDrawingOrderCallback
to be used for drawing children.
See getChildDrawingOrder(int, int)
for details. Calling this method will always call setChildrenDrawingOrderEnabled(boolean)
. The parameter will be true if childDrawingOrderCallback is not null, false otherwise.
Note that child drawing order may be overridden by View's elevation.
childDrawingOrderCallback | The ChildDrawingOrderCallback to be used by the drawing system. |
---|
Sets whether this ViewGroup will clip its children to its padding and resize (but not clip) any EdgeEffect to the padded region, if padding is present.
By default, children are clipped to the padding of their parent ViewGroup. This clipping behavior is only enabled if padding is non-zero.
clipToPadding | true to clip children to the padding of the group, and resize (but not clip) any EdgeEffect to the padded region. False otherwise. |
---|
RecyclerView can perform several optimizations if it can know in advance that changes in adapter content cannot change the size of the RecyclerView itself. If your use of RecyclerView falls into this category, set this to true.
hasFixedSize | true if adapter changes cannot affect the size of the RecyclerView. |
---|
Sets the RecyclerView.ItemAnimator
that will handle animations involving changes to the items in this RecyclerView. By default, RecyclerView instantiates and uses an instance of DefaultItemAnimator
. Whether item animations are enabled for the RecyclerView depends on the ItemAnimator and whether the LayoutManager supports item animations
.
animator | The ItemAnimator being set. If null, no animations will occur when changes occur to the items in this RecyclerView. |
---|
Set the number of offscreen views to retain before adding them to the potentially shared recycled view pool
.
The offscreen view cache stays aware of changes in the attached adapter, allowing a LayoutManager to reuse those views unmodified without needing to return to the adapter to rebind them.
size | Number of views to cache offscreen before returning them to the general recycled view pool |
---|
Enable or disable layout and scroll. After setLayoutFrozen(true)
is called, Layout requests will be postponed until setLayoutFrozen(false)
is called; child views are not updated when RecyclerView is frozen, smoothScrollBy(int, int)
, scrollBy(int, int)
, scrollToPosition(int)
and smoothScrollToPosition(int)
are dropped; TouchEvents and GenericMotionEvents are dropped; onFocusSearchFailed(View, int, Recycler, State)
will not be called.
setLayoutFrozen(true)
does not prevent app from directly calling scrollToPosition(int)
, smoothScrollToPosition(RecyclerView, State, int)
.
setAdapter(Adapter)
and swapAdapter(Adapter, boolean)
will automatically stop frozen.
Note: Running ItemAnimator is not stopped automatically, it's caller's responsibility to call ItemAnimator.end().
frozen | true to freeze layout and scroll, false to re-enable. |
---|
Set the RecyclerView.LayoutManager
that this RecyclerView will use.
In contrast to other adapter-backed views such as ListView
or GridView
, RecyclerView allows client code to provide custom layout arrangements for child views. These arrangements are controlled by the RecyclerView.LayoutManager
. A LayoutManager must be provided for RecyclerView to function.
Several default strategies are provided for common uses such as lists and grids.
layout | LayoutManager to use |
---|
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.
enabled | true to enable nested scrolling, false to disable |
---|
This method is deprecated.
Use addOnScrollListener(OnScrollListener)
and removeOnScrollListener(OnScrollListener)
Set a listener that will be notified of any changes in scroll state or position.
listener | Listener to set or null to clear |
---|
Recycled view pools allow multiple RecyclerViews to share a common pool of scrap views. This can be useful if you have multiple RecyclerViews with adapters that use the same view types, for example if you have several data sets with the same kinds of item views displayed by a ViewPager
.
pool | Pool to set. If this parameter is null a new pool will be created and used. |
---|
Register a listener that will be notified whenever a child view is recycled.
This listener will be called when a LayoutManager or the RecyclerView decides that a child view is no longer needed. If an application associates expensive or heavyweight data with item views, this may be a good place to release or free those resources.
listener | Listener to register, or null to clear |
---|
Configure the scrolling touch slop for a specific use case. Set up the RecyclerView's scrolling motion threshold based on common usages. Valid arguments areTOUCH_SLOP_DEFAULT
and TOUCH_SLOP_PAGING
.
slopConstant | One of the TOUCH_SLOP_ constants representing the intended usage of this RecyclerView |
---|
Sets a new RecyclerView.ViewCacheExtension
to be used by the Recycler.
extension | ViewCacheExtension to be used or null if you want to clear the existing one. |
---|
ERROR(ViewCacheExtension#getViewForPositionAndType(Recycler, int, int)} /{@link ViewCacheExtension#getViewForPositionAndType(Recycler, int, int)})
Animate a scroll by the given amount of pixels along either axis.
dx | Pixels to scroll horizontally |
---|---|
dy | Pixels to scroll vertically |
Starts a smooth scroll to an adapter position.
To support smooth scrolling, you must override smoothScrollToPosition(RecyclerView, State, int)
and create a RecyclerView.SmoothScroller
.
RecyclerView.LayoutManager
is responsible for creating the actual scroll action. If you want to provide a custom smooth scroll logic, overridesmoothScrollToPosition(RecyclerView, State, int)
in your LayoutManager.
position | The adapter position to scroll to |
---|
smoothScrollToPosition(RecyclerView, State, int)
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)
.
axes | Flags consisting of a combination of SCROLL_AXIS_HORIZONTAL and/or SCROLL_AXIS_VERTICAL . |
---|
Stop a nested scroll in progress.
Calling this method when a nested scroll is not currently in progress is harmless.
Stop any current scroll in progress, such as one started by smoothScrollBy(int, int)
, fling(int, int)
or a touch-initiated fling.
Swaps the current adapter with the provided one. It is similar to setAdapter(Adapter)
but assumes existing adapter and the new adapter uses the sameRecyclerView.ViewHolder
and does not clear the RecycledViewPool.
Note that it still calls onAdapterChanged callbacks.
adapter | The new adapter to set, or null to set no adapter. |
---|---|
removeAndRecycleExistingViews | If set to true, RecyclerView will recycle all existing Views. If adapters have stable ids and/or you want to animate the disappearing views, you may prefer to set this to false. |
setAdapter(Adapter)
Override to prevent thawing of any views created by the adapter.
container | The SparseArray which holds previously saved state. |
---|
Override to prevent freezing of any views created by the adapter.
container | The SparseArray in which to save the view's state. |
---|
Returns a set of default layout parameters. These parameters are requested when the View passed to addView(View)
has no layout parameters already set. If null is returned, an exception is thrown from addView.
Returns a safe set of layout parameters based on the supplied layout params. When a ViewGroup is passed a View whose layout params do not pass the test ofcheckLayoutParams(android.view.ViewGroup.LayoutParams)
, this method is invoked. This method should return a new set of layout params suitable for this ViewGroup, possibly by copying the appropriate attributes from the specified set of layout params.
p | The layout parameters to convert into a suitable set of layout parameters for this ViewGroup. |
---|
ViewGroup.LayoutParams
or one of its descendantsReturns the index of the child to draw for this iteration. Override this if you want to change the drawing order of children. By default, it returns i.
NOTE: In order for this method to be called, you must enable child ordering first by calling setChildrenDrawingOrderEnabled(boolean)
.
i | The current iteration. |
---|
This is called when the view is attached to a window. At this point it has a Surface and will start drawing. Note that this function is guaranteed to be called beforeonDraw(android.graphics.Canvas)
, however it may be called any time before the first onDraw -- including before or after onMeasure(int, int)
.
This is called when the view is detached from a window. At this point it no longer has a surface for drawing.
Called from layout when this view should assign a size and position to each of its children. Derived classes with children should override this method and call layout on each of their children.
changed | This is a new size or position for this view |
---|---|
l | Left position, relative to parent |
t | Top position, relative to parent |
r | Right position, relative to parent |
b | Bottom position, relative to parent |
Measure the view and its content to determine the measured width and the measured height. This method is invoked by measure(int, int)
and should be overridden by subclasses to provide accurate and efficient measurement of their contents.
CONTRACT: When overriding this method, you must call setMeasuredDimension(int, int)
to store the measured width and height of this view. Failure to do so will trigger an IllegalStateException
, thrown by measure(int, int)
. Calling the superclass' onMeasure(int, int)
is a valid use.
The base class implementation of measure defaults to the background size, unless a larger size is allowed by the MeasureSpec. Subclasses should overrideonMeasure(int, int)
to provide better measurements of their content.
If this method is overridden, it is the subclass's responsibility to make sure the measured height and width are at least the view's minimum height and width (getSuggestedMinimumHeight()
and getSuggestedMinimumWidth()
).
widthSpec | horizontal space requirements as imposed by the parent. The requirements are encoded with View.MeasureSpec . |
---|---|
heightSpec | vertical space requirements as imposed by the parent. The requirements are encoded with View.MeasureSpec . |
Hook allowing a view to re-apply a representation of its internal state that had previously been generated by onSaveInstanceState()
. This function will never be called with a null state.
state | The frozen state that had previously been returned by onSaveInstanceState() . |
---|
Hook allowing a view to generate a representation of its internal state that can later be used to create a new instance with that same state. This state should only contain information that is not persistent or can not be reconstructed later. For example, you will never store your current position on screen because that will be computed again when a new instance of the view is placed in its view hierarchy.
Some examples of things you may store here: the current cursor position in a text view (but usually not the text itself since that is stored in a content provider or other persistent storage), the currently selected item in a list view.
This is called during layout when the size of this view has changed. If you were just added to the view hierarchy, you're called with the old values of 0.
w | Current width of this view. |
---|---|
h | Current height of this view. |
oldw | Old width of this view. |
oldh | Old height of this view. |
Finishes the removal of a detached view. This method will dispatch the detached from window event and notify the hierarchy change listener.
This method is intended to be lightweight and makes no assumptions about whether the parent or child should be redrawn. Proper use of this method will include also making any appropriate requestLayout()
or invalidate()
calls. For example, callers can post
a Runnable
which performs a requestLayout()
on the next frame, after all detach/remove calls are finished, causing layout to be run prior to redrawing the view hierarchy.
child | the child to be definitely removed from the view hierarchy |
---|---|
animate | if true and the view has an animation, the view is placed in the disappearing views list, otherwise, it is detached from the window |
.