【Android应用开发】RecycleView API 翻译 (文档翻译)

RecyclerView extends  ViewGroup implements  ScrollingView NestedScrollingChild

Known Direct Subclasses
HorizontalGridView,  VerticalGridView

类概述

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.

术语表:

• Adapter(适配器): 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.
• Position(位置): 适配器(Adapter)中的数据项目位置.
• Index(索引): 一个已经附加的子组件的索引在getChildAt(int)方法中使用. 与Position形成对比.
• Binding(绑定进程): 适配器中需要一个显示Position对应的数据的子组件,Binding就是准备该子组件的进程.
• Recycle (view): 该View之前曾用于显示指定适配器位置的数据,那么这个View可能会被放置在一个缓存中,以便可以在之后被复用去显示同样类型的数据.上述操作可以跳过布局文件的初始化加载或创建, 这样就可以很大程度上提高应用的性能.
• Scrap (view): 在布局过程中,一个已经进入暂时分离状态子组件.在不用完全从父类RecycleView中分离的情况下,该Scrap View可以被复用.如果组件被认为是作废的,那么重新绑定数据与组件和改变适配器不是必须的,不用作出改变.
• Dirty (view): 一个子组件在显示之前,必须被适配器(Adapter)重新绑定.

RecyclerView中的位置(Position): 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:

• 布局位置 (layout position): 最近的一次布局计算的项目位置. 这个位置(Position)是以布局管理器 (LayoutManager) 的角度来说的.
• 适配器位置 (adapter position): 适配器(Adapter)项目(Item)的位置. 这个位置(Position)是以适配器(Adapter)的角度来说的.

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). Summary

XML Attributes

android.support.v7.recyclerview:layoutManager

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.

Related Methods

Constants

public static final int HORIZONTAL

Constant Value: 0 (0x00000000)

public static final int INVALID_TYPE

Constant Value: -1 (0xffffffff)

public static final long NO_ID

Constant Value: -1 (0xffffffffffffffff)

public static final int NO_POSITION

Constant Value: -1 (0xffffffff)

public static final int SCROLL_STATE_DRAGGING

The RecyclerView is currently being dragged by outside input such as user touch input.

See Also

• getScrollState()

Constant Value: 1 (0x00000001)

public static final int SCROLL_STATE_IDLE

The RecyclerView is not currently scrolling.

See Also

• getScrollState()

Constant Value: 0 (0x00000000)

public static final int SCROLL_STATE_SETTLING

The RecyclerView is currently animating to a final position while not under outside control.

See Also

• getScrollState()

Constant Value: 2 (0x00000002)

public static final int TOUCH_SLOP_DEFAULT

Constant for use with setScrollingTouchSlop(int). Indicates that the RecyclerView should use the standard touch slop for smooth, continuous scrolling.

Constant Value: 0 (0x00000000)

public static final int TOUCH_SLOP_PAGING

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.

Constant Value: 1 (0x00000001)

public static final int VERTICAL

Constant Value: 1 (0x00000001)

Public Constructors

public RecyclerView (Context context)

public RecyclerView (Context context, AttributeSet attrs)

public RecyclerView (Context context, AttributeSet attrs, int defStyle)

Public Methods

public void addFocusables (ArrayList<View> views, int direction, int focusableMode)

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.

Parameters

public void addItemDecoration (RecyclerView.ItemDecoration decor)

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.

Parameters

public void addItemDecoration (RecyclerView.ItemDecoration decor, int index)

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.

Parameters

public void addOnChildAttachStateChangeListener (RecyclerView.OnChildAttachStateChangeListener listener)

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.

Parameters

public void addOnItemTouchListener (RecyclerView.OnItemTouchListener listener)

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.

Parameters

See Also

• RecyclerView.SimpleOnItemTouchListener

public void addOnScrollListener (RecyclerView.OnScrollListener listener)

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.

Parameters

public void clearOnChildAttachStateChangeListeners ()

Removes all listeners that were added via addOnChildAttachStateChangeListener(OnChildAttachStateChangeListener).

public void clearOnScrollListeners ()

Remove all secondary listener that were notified of any changes in scroll state or position.

public int computeHorizontalScrollExtent ()

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.

Returns

• The horizontal extent of the scrollbar's thumb

See Also

• computeHorizontalScrollExtent(RecyclerView.State)

public int computeHorizontalScrollOffset ()

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.

Returns

• The horizontal offset of the scrollbar's thumb

See Also

• (RecyclerView.Adapter)

public int computeHorizontalScrollRange ()

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.

Returns

• The total horizontal range represented by the vertical scrollbar

See Also

• computeHorizontalScrollRange(RecyclerView.State)

public int computeVerticalScrollExtent ()

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.

Returns

• The vertical extent of the scrollbar's thumb

See Also

• computeVerticalScrollExtent(RecyclerView.State)

public int computeVerticalScrollOffset ()

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.

Returns

• The vertical offset of the scrollbar's thumb

See Also

• (RecyclerView.Adapter)

public int computeVerticalScrollRange ()

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.

Returns

• The total vertical range represented by the vertical scrollbar

See Also

• computeVerticalScrollRange(RecyclerView.State)

public 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

Returns

• true if the nested scrolling parent consumed or otherwise reacted to the fling

public 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

Returns

• true if a nested scrolling parent consumed the fling

public 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

Returns

• true if the parent consumed some or all of the scroll delta

public 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

Returns

• true if the event was dispatched, false if it could not be dispatched.

public void draw (Canvas c)

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.

Parameters

public boolean drawChild (Canvas canvas, View child, long drawingTime)

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.

Parameters

Returns

• True if an invalidate() was issued

public View findChildViewUnder (float x, float y)

Find the topmost view under the given point.

Parameters

Returns

• The child view under (x, y) or null if no matching child is found

public RecyclerView.ViewHolder findViewHolderForAdapterPosition (int position)

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.

Parameters

Returns

• The ViewHolder at position or null if there is no such item

public RecyclerView.ViewHolder findViewHolderForItemId (long id)

Return 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.

Parameters

Returns

• The ViewHolder with the given id or null if there is no such item

public RecyclerView.ViewHolder findViewHolderForLayoutPosition (int position)

Return 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.

Parameters

Returns

• The ViewHolder at position or null if there is no such item

public RecyclerView.ViewHolder findViewHolderForPosition (int position)

This method is deprecated. use findViewHolderForLayoutPosition(int) or findViewHolderForAdapterPosition(int)

public boolean fling (int velocityX, int velocityY)

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.

Parameters

Returns

• true if the fling was started, false if the velocity was too low to fling or LayoutManager does not support scrolling in the axis fling is issued.

See Also

• canScrollVertically()
• canScrollHorizontally()

public View focusSearch (View focused, int direction)

Find the nearest view in the specified direction that wants to take focus.

Parameters

public ViewGroup.LayoutParams generateLayoutParams (AttributeSet attrs)

Returns a new set of layout parameters based on the supplied attributes set.

Parameters

Returns

• an instance of ViewGroup.LayoutParams or one of its descendants

public Adapter getAdapter ()

Retrieves the previously set adapter or null if no adapter is set.

Returns

• The previously set adapter

See Also

• setAdapter(Adapter)

public int getBaseline ()

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.

Returns

• the offset of the baseline within the RecyclerView's bounds or -1 if baseline alignment is not supported

public int getChildAdapterPosition (View child)

Return the adapter position that the given child view corresponds to.

Parameters

Returns

• Adapter position corresponding to the given view or NO_POSITION

public long getChildItemId (View child)

Return the stable item id that the given child view corresponds to.

Parameters

Returns

• Item id corresponding to the given view or NO_ID

public int getChildLayoutPosition (View child)

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.

Parameters

Returns

• Adapter position of the given View as of last layout pass or NO_POSITION if the View is representing a removed item.

public int getChildPosition (View child)

This method is deprecated. use getChildAdapterPosition(View) or getChildLayoutPosition(View).

public RecyclerView.ViewHolder getChildViewHolder (View child)

Retrieve the RecyclerView.ViewHolder for the given child view.

Parameters

Returns

• The child view's ViewHolder

public RecyclerViewAccessibilityDelegate getCompatAccessibilityDelegate ()

Returns the accessibility delegate compatibility implementation used by the RecyclerView.

Returns

• An instance of AccessibilityDelegateCompat used by RecyclerView

public RecyclerView.ItemAnimator getItemAnimator ()

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.

Returns

• ItemAnimator The current ItemAnimator. If null, no animations will occur when changes occur to the items in this RecyclerView.

public RecyclerView.LayoutManager getLayoutManager ()

Return the RecyclerView.LayoutManager currently responsible for layout policy for this RecyclerView.

Returns

• The currently bound LayoutManager

public int getMaxFlingVelocity ()

Returns the maximum fling velocity used by this RecyclerView.

Returns

• The maximum fling velocity used by this RecyclerView.

public int getMinFlingVelocity ()

Returns the minimum velocity to start a fling.

Returns

• The minimum velocity to start a fling

public RecyclerView.RecycledViewPool getRecycledViewPool ()

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.

Returns

• The pool used to store recycled item views for reuse.

See Also

• setRecycledViewPool(RecycledViewPool)

public int getScrollState ()

Return the current scrolling state of the RecyclerView.

Returns

• SCROLL_STATE_IDLE, SCROLL_STATE_DRAGGING or SCROLL_STATE_SETTLING

public boolean hasFixedSize ()

Returns

• true if the app has specified that changes in adapter content cannot change the size of the RecyclerView itself.

public 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

• whether this view has a nested scrolling parent

public boolean hasPendingAdapterUpdates ()

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.

Returns

• True if there are some adapter updates which are not yet reflected to layout or false if layout is up to date.

public void invalidateItemDecorations ()

Invalidates all ItemDecorations. If RecyclerView has item decorations, calling this method will trigger a requestLayout() call.

public boolean isAnimating ()

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 there are some item animations currently running or waiting to be started.

public boolean isAttachedToWindow ()

Returns true if RecyclerView is attached to window.

public boolean isComputingLayout ()

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.

Returns

• true if RecyclerView is currently computing a layout, false otherwise

public boolean isLayoutFrozen ()

Returns true if layout and scroll are frozen.

Returns

• true if layout and scroll are frozen

See Also

• setLayoutFrozen(boolean)

public 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

• true if nested scrolling is enabled

public void offsetChildrenHorizontal (int dx)

Offset the bounds of all child views by dx pixels. Useful for implementing simple scrolling in LayoutManagers.

Parameters

public void offsetChildrenVertical (int dy)

Offset the bounds of all child views by dy pixels. Useful for implementing simple scrolling in LayoutManagers.

Parameters

public void onChildAttachedToWindow (View child)

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.

Parameters

public void onChildDetachedFromWindow (View child)

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.

Parameters

public void onDraw (Canvas c)

Implement this to do your drawing.

Parameters

public boolean onGenericMotionEvent (MotionEvent event)

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);
 }

Parameters

Returns

• True if the event was handled, false otherwise.

public boolean onInterceptTouchEvent (MotionEvent e)

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:

1. You will receive the down event here.
2. The down event will be handled either by a child of this view group, or given to your own onTouchEvent() method to handle; this means you should implement onTouchEvent() to return true, so you will continue to see the rest of the gesture (instead of looking for a parent view to handle it). Also, by returning true from onTouchEvent(), you will not receive any following events in onInterceptTouchEvent() and all touch processing must happen in onTouchEvent() like normal.
3. For as long as you return false from this function, each following event (up to and including the final up) will be delivered first here and then to the target's onTouchEvent().
4. If you return true from here, you will not receive any following events: the target view will receive the same event but with the action ACTION_CANCEL, and all further events will be delivered to your onTouchEvent() method and no longer appear here.

Parameters

Returns

• Return true to steal motion events from the children and have them dispatched to this ViewGroup through onTouchEvent(). The current target will receive an ACTION_CANCEL event, and no further messages will be delivered here.

public void onScrollStateChanged (int state)

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.

Parameters

public void onScrolled (int dx, int dy)

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.

Parameters

public boolean onTouchEvent (MotionEvent e)

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:

• obeying click sound preferences
• dispatching OnClickListener calls
• handling ACTION_CLICK when accessibility features are enabled

Parameters

Returns

• True if the event was handled, false otherwise.

public void removeItemDecoration (RecyclerView.ItemDecoration decor)

Remove an RecyclerView.ItemDecoration from this RecyclerView.

The given decoration will no longer impact the measurement and drawing of item views.

Parameters

See Also

• addItemDecoration(ItemDecoration)

public void removeOnChildAttachStateChangeListener (RecyclerView.OnChildAttachStateChangeListener listener)

Removes the provided listener from child attached state listeners list.

Parameters

public void removeOnItemTouchListener (RecyclerView.OnItemTouchListener listener)

Remove an RecyclerView.OnItemTouchListener. It will no longer be able to intercept touch events.

Parameters

public void removeOnScrollListener (RecyclerView.OnScrollListener listener)

Remove a listener that was notified of any changes in scroll state or position.

Parameters

public void requestChildFocus (View child, View focused)

Called when a child of this parent wants focus

Parameters

public 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. ViewGroups overriding this can trust that:

• child will be a direct child of this group
• rectangle will be in the child's coordinates

ViewGroups overriding this should uphold the contract:

• nothing will change if the rectangle is already visible
• the view port will be scrolled only just enough to make the rectangle visible

Parameters

Returns

• Whether the group scrolled to handle the operation

public void requestDisallowInterceptTouchEvent (boolean disallowIntercept)

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.

Parameters

public void requestLayout ()

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.

public void scrollBy (int x, int y)

Move the scrolled position of your view. This will cause a call to onScrollChanged(int, int, int, int) and the view will be invalidated.

Parameters

public void scrollTo (int x, int y)

Set the scrolled position of your view. This will cause a call to onScrollChanged(int, int, int, int) and the view will be invalidated.

Parameters

public void scrollToPosition (int position)

Convenience method to scroll to a certain position. RecyclerView does not implement scrolling logic, rather forwards the call to scrollToPosition(int)

Parameters

See Also

• scrollToPosition(int)

public 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.

If an View.AccessibilityDelegate has been specified via calling setAccessibilityDelegate(AccessibilityDelegate) itssendAccessibilityEventUnchecked(View, AccessibilityEvent) is responsible for handling this call.

Parameters

public void setAccessibilityDelegateCompat (RecyclerViewAccessibilityDelegate accessibilityDelegate)

Sets the accessibility delegate compatibility implementation used by RecyclerView.

Parameters

public void setAdapter (Adapter adapter)

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.

Parameters

See Also

• swapAdapter(Adapter, boolean)

public void setChildDrawingOrderCallback (RecyclerView.ChildDrawingOrderCallback childDrawingOrderCallback)

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.

Parameters

public 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.

By default, children are clipped to the padding of their parent ViewGroup. This clipping behavior is only enabled if padding is non-zero.

Parameters

public 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. If your use of RecyclerView falls into this category, set this to true.

Parameters

public void setItemAnimator (RecyclerView.ItemAnimator animator)

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.

Parameters

public void setItemViewCacheSize (int size)

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.

Parameters

public void setLayoutFrozen (boolean frozen)

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().

Parameters

public void setLayoutManager (RecyclerView.LayoutManager layout)

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.

Parameters

public 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

public void setOnScrollListener (RecyclerView.OnScrollListener listener)

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.

Parameters

public void setRecycledViewPool (RecyclerView.RecycledViewPool pool)

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.

Parameters

public void setRecyclerListener (RecyclerView.RecyclerListener listener)

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.

Parameters

public void setScrollingTouchSlop (int slopConstant)

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.

Parameters

public void setViewCacheExtension (RecyclerView.ViewCacheExtension extension)

Sets a new RecyclerView.ViewCacheExtension to be used by the Recycler.

Parameters

See Also

• ERROR(ViewCacheExtension#getViewForPositionAndType(Recycler, int, int)} /{@link ViewCacheExtension#getViewForPositionAndType(Recycler, int, int)})

public void smoothScrollBy (int dx, int dy)

Animate a scroll by the given amount of pixels along either axis.

Parameters

public void smoothScrollToPosition (int position)

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.

Parameters

See Also

• smoothScrollToPosition(RecyclerView, State, int)

public 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

Returns

• true if a cooperative parent was found and nested scrolling has been enabled for the current gesture.

public void stopNestedScroll ()

Stop a nested scroll in progress.

Calling this method when a nested scroll is not currently in progress is harmless.

public void stopScroll ()

Stop any current scroll in progress, such as one started by smoothScrollBy(int, int), fling(int, int) or a touch-initiated fling.

public void swapAdapter (Adapter adapter, boolean removeAndRecycleExistingViews)

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.

Parameters

See Also

• setAdapter(Adapter)

Protected Methods

protected boolean checkLayoutParams (ViewGroup.LayoutParams p)

protected void dispatchRestoreInstanceState (SparseArray<Parcelable> container)

Override to prevent thawing of any views created by the adapter.

Parameters

protected void dispatchSaveInstanceState (SparseArray<Parcelable> container)

Override to prevent freezing of any views created by the adapter.

Parameters

protected ViewGroup.LayoutParams generateDefaultLayoutParams ()

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 set of default layout parameters or null

protected ViewGroup.LayoutParams generateLayoutParams (ViewGroup.LayoutParams p)

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.

Parameters

Returns

• an instance of ViewGroup.LayoutParams or one of its descendants

protected int getChildDrawingOrder (int childCount, int i)

Returns 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).

Parameters

Returns

• The index of the child to draw this iteration.

protected void onAttachedToWindow ()

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).

protected void onDetachedFromWindow ()

This is called when the view is detached from a window. At this point it no longer has a surface for drawing.

protected 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. Derived classes with children should override this method and call layout on each of their children.

Parameters

protected void onMeasure (int widthSpec, int heightSpec)

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()).

Parameters

protected void onRestoreInstanceState (Parcelable state)

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.

Parameters

protected 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. 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.

Returns

• Returns a Parcelable object containing the view's current dynamic state, or null if there is nothing interesting to save. The default implementation returns null.

protected void onSizeChanged (int w, int h, int oldw, int oldh)

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.

Parameters

protected void removeDetachedView (View child, boolean animate)

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.

Parameters