public abstract class

ExploreByTouchHelper

extends AccessibilityDelegateCompat

 java.lang.Object

androidx.core.view.AccessibilityDelegateCompat

↳androidx.customview.widget.ExploreByTouchHelper

Gradle dependencies

compile group: 'androidx.customview', name: 'customview', version: '1.2.0-alpha01'

  • groupId: androidx.customview
  • artifactId: customview
  • version: 1.2.0-alpha01

Artifact androidx.customview:customview:1.2.0-alpha01 it located at Google repository (https://maven.google.com/)

Androidx artifact mapping:

androidx.customview:customview com.android.support:customview

Androidx class mapping:

androidx.customview.widget.ExploreByTouchHelper android.support.v4.widget.ExploreByTouchHelper

Overview

ExploreByTouchHelper is a utility class for implementing accessibility support in custom Views that represent a collection of View-like logical items. It extends AccessibilityNodeProviderCompat and simplifies many aspects of providing information to accessibility services and managing accessibility focus.

Clients should override abstract methods on this class and attach it to the host view using ViewCompat.setAccessibilityDelegate(View, AccessibilityDelegateCompat).

The host view should also override the events in the following code snippet so that the view's logical items are detected properly by the framework:

 class MyCustomView extends View {
     private MyExploreByTouchHelper mExploreByTouchHelper;

     public MyCustomView(Context context, ...) {
         ...
         mExploreByTouchHelper = new MyExploreByTouchHelper(this);
         ViewCompat.setAccessibilityDelegate(this, mExploreByTouchHelper);
     }

     @Override
     public boolean dispatchHoverEvent(MotionEvent event) {
       return mHelper.dispatchHoverEvent(this, event)
           || super.dispatchHoverEvent(event);
     }

     @Override
     public boolean dispatchKeyEvent(KeyEvent event) {
       return mHelper.dispatchKeyEvent(event)
           || super.dispatchKeyEvent(event);
     }

     @Override
     public void onFocusChanged(boolean gainFocus, int direction,
         Rect previouslyFocusedRect) {
       super.onFocusChanged(gainFocus, direction, previouslyFocusedRect);
       mHelper.onFocusChanged(gainFocus, direction, previouslyFocusedRect);
     }
 }
 

Summary

Fields
public static final intHOST_ID

Virtual node identifier value for the host view's node.

public static final intINVALID_ID

Virtual node identifier value for invalid nodes.

Constructors
publicExploreByTouchHelper(View host)

Constructs a new helper that can expose a virtual view hierarchy for the specified host view.

Methods
public final booleanclearKeyboardFocusForVirtualView(int virtualViewId)

Attempts to clear keyboard focus from a virtual view.

public final booleandispatchHoverEvent(MotionEvent event)

Delegates hover events from the host view.

public final booleandispatchKeyEvent(KeyEvent event)

Delegates key events from the host view.

public final intgetAccessibilityFocusedVirtualViewId()

public AccessibilityNodeProviderCompatgetAccessibilityNodeProvider(View host)

Gets the provider for managing a virtual view hierarchy rooted at this View and reported to s that explore the window content.

public intgetFocusedVirtualView()

Returns the virtual view ID for the currently accessibility focused item.

public final intgetKeyboardFocusedVirtualViewId()

protected abstract intgetVirtualViewAt(float x, float y)

Provides a mapping between view-relative coordinates and logical items.

protected abstract voidgetVisibleVirtualViews(java.util.List<java.lang.Integer> virtualViewIds)

Populates a list with the view's visible items.

public final voidinvalidateRoot()

Notifies the accessibility framework that the properties of the parent view have changed.

public final voidinvalidateVirtualView(int virtualViewId)

Notifies the accessibility framework that the properties of a particular item have changed.

public final voidinvalidateVirtualView(int virtualViewId, int changeTypes)

Notifies the accessibility framework that the properties of a particular item have changed.

public final voidonFocusChanged(boolean gainFocus, int direction, Rect previouslyFocusedRect)

Delegates focus changes from the host view.

public voidonInitializeAccessibilityEvent(View host, AccessibilityEvent event)

Initializes an with information about the the host View which is the event source.

public voidonInitializeAccessibilityNodeInfo(View host, AccessibilityNodeInfoCompat info)

Initializes an AccessibilityNodeInfoCompat with information about the host view.

protected abstract booleanonPerformActionForVirtualView(int virtualViewId, int action, Bundle arguments)

Performs the specified accessibility action on the item associated with the virtual view identifier.

protected voidonPopulateEventForHost(AccessibilityEvent event)

Populates an with information about the host view.

protected voidonPopulateEventForVirtualView(int virtualViewId, AccessibilityEvent event)

Populates an with information about the specified item.

protected voidonPopulateNodeForHost(AccessibilityNodeInfoCompat node)

Populates an AccessibilityNodeInfoCompat with information about the host view.

protected abstract voidonPopulateNodeForVirtualView(int virtualViewId, AccessibilityNodeInfoCompat node)

Populates an AccessibilityNodeInfoCompat with information about the specified item.

protected voidonVirtualViewKeyboardFocusChanged(int virtualViewId, boolean hasFocus)

Called when the focus state of a virtual view changes.

public final booleanrequestKeyboardFocusForVirtualView(int virtualViewId)

Attempts to give keyboard focus to a virtual view.

public final booleansendEventForVirtualView(int virtualViewId, int eventType)

Populates an event of the specified type with information about an item and attempts to send it up through the view hierarchy.

public final voidsetBoundsInScreenFromBoundsInParent(AccessibilityNodeInfoCompat node, Rect boundsInParent)

Calculates and assigns screen-relative bounds based on bounds in parent.

from AccessibilityDelegateCompatdispatchPopulateAccessibilityEvent, onPopulateAccessibilityEvent, onRequestSendAccessibilityEvent, performAccessibilityAction, sendAccessibilityEvent, sendAccessibilityEventUnchecked
from java.lang.Objectclone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Fields

public static final int INVALID_ID

Virtual node identifier value for invalid nodes.

public static final int HOST_ID

Virtual node identifier value for the host view's node.

Constructors

public ExploreByTouchHelper(View host)

Constructs a new helper that can expose a virtual view hierarchy for the specified host view.

Parameters:

host: view whose virtual view hierarchy is exposed by this helper

Methods

public AccessibilityNodeProviderCompat getAccessibilityNodeProvider(View host)

Gets the provider for managing a virtual view hierarchy rooted at this View and reported to s that explore the window content.

The default implementation behaves as ViewCompat#getAccessibilityNodeProvider(View) for the case of no accessibility delegate been set.

Returns:

The provider.

See also: AccessibilityNodeProviderCompat

public final boolean dispatchHoverEvent(MotionEvent event)

Delegates hover events from the host view.

Dispatches hover MotionEvents to the virtual view hierarchy when the Explore by Touch feature is enabled.

This method should be called by overriding the host view's View method:

@Override
 public boolean dispatchHoverEvent(MotionEvent event) {
   return mHelper.dispatchHoverEvent(this, event)
       || super.dispatchHoverEvent(event);
 }
 

Parameters:

event: The hover event to dispatch to the virtual view hierarchy.

Returns:

Whether the hover event was handled.

public final boolean dispatchKeyEvent(KeyEvent event)

Delegates key events from the host view.

This method should be called by overriding the host view's View method:

@Override
 public boolean dispatchKeyEvent(KeyEvent event) {
   return mHelper.dispatchKeyEvent(event)
       || super.dispatchKeyEvent(event);
 }
 

public final void onFocusChanged(boolean gainFocus, int direction, Rect previouslyFocusedRect)

Delegates focus changes from the host view.

This method should be called by overriding the host view's View method:

@Override
 public boolean onFocusChanged(boolean gainFocus, int direction,
     Rect previouslyFocusedRect) {
   super.onFocusChanged(gainFocus, direction, previouslyFocusedRect);
   mHelper.onFocusChanged(gainFocus, direction, previouslyFocusedRect);
 }
 

public final int getAccessibilityFocusedVirtualViewId()

Returns:

the identifier of the virtual view that has accessibility focus or ExploreByTouchHelper.INVALID_ID if no virtual view has accessibility focus

public final int getKeyboardFocusedVirtualViewId()

Returns:

the identifier of the virtual view that has keyboard focus or ExploreByTouchHelper.INVALID_ID if no virtual view has keyboard focus

public final boolean sendEventForVirtualView(int virtualViewId, int eventType)

Populates an event of the specified type with information about an item and attempts to send it up through the view hierarchy.

You should call this method after performing a user action that normally fires an accessibility event, such as clicking on an item.

public void performItemClick(T item) {
   ...
   sendEventForVirtualViewId(item.id, AccessibilityEvent.TYPE_VIEW_CLICKED);
 }
 

Parameters:

virtualViewId: the identifier of the virtual view for which to send an event
eventType: the type of event to send

Returns:

true if the event was sent successfully, false otherwise

public final void invalidateRoot()

Notifies the accessibility framework that the properties of the parent view have changed.

You must call this method after adding or removing items from the parent view.

public final void invalidateVirtualView(int virtualViewId)

Notifies the accessibility framework that the properties of a particular item have changed.

You must call this method after changing any of the properties set in ExploreByTouchHelper.onPopulateNodeForVirtualView(int, AccessibilityNodeInfoCompat).

Parameters:

virtualViewId: the virtual view id to invalidate, or ExploreByTouchHelper.HOST_ID to invalidate the root view

See also: ExploreByTouchHelper.invalidateVirtualView(int, int)

public final void invalidateVirtualView(int virtualViewId, int changeTypes)

Notifies the accessibility framework that the properties of a particular item have changed.

You must call this method after changing any of the properties set in ExploreByTouchHelper.onPopulateNodeForVirtualView(int, AccessibilityNodeInfoCompat).

Parameters:

virtualViewId: the virtual view id to invalidate, or ExploreByTouchHelper.HOST_ID to invalidate the root view
changeTypes: the bit mask of change types. May be 0 for the default (undefined) change type or one or more of:


public int getFocusedVirtualView()

Deprecated: Use ExploreByTouchHelper.getAccessibilityFocusedVirtualViewId().

Returns the virtual view ID for the currently accessibility focused item.

Returns:

the identifier of the virtual view that has accessibility focus or ExploreByTouchHelper.INVALID_ID if no virtual view has accessibility focus

protected void onVirtualViewKeyboardFocusChanged(int virtualViewId, boolean hasFocus)

Called when the focus state of a virtual view changes.

Parameters:

virtualViewId: the virtual view identifier
hasFocus: true if the view has focus, false otherwise

public void onInitializeAccessibilityEvent(View host, AccessibilityEvent event)

Initializes an with information about the the host View which is the event source.

The default implementation behaves as ViewCompat#onInitalizeAccessibilityEvent(View v, AccessibilityEvent event) for the case of no accessibility delegate been set.

Parameters:

host: The View hosting the delegate.
event: The event to initialize.

See also: ViewCompat#onInitializeAccessibilityEvent(View, AccessibilityEvent)

public void onInitializeAccessibilityNodeInfo(View host, AccessibilityNodeInfoCompat info)

Initializes an AccessibilityNodeInfoCompat with information about the host view.

The default implementation behaves as ViewCompat#onInitializeAccessibilityNodeInfo(View, AccessibilityNodeInfoCompat) for the case of no accessibility delegate been set.

Parameters:

host: The View hosting the delegate.
info: The instance to initialize.

See also: ViewCompat#onInitializeAccessibilityNodeInfo(View, AccessibilityNodeInfoCompat)

public final boolean requestKeyboardFocusForVirtualView(int virtualViewId)

Attempts to give keyboard focus to a virtual view.

Parameters:

virtualViewId: the identifier of the virtual view on which to place keyboard focus

Returns:

whether this virtual view actually took keyboard focus

public final boolean clearKeyboardFocusForVirtualView(int virtualViewId)

Attempts to clear keyboard focus from a virtual view.

Parameters:

virtualViewId: the identifier of the virtual view from which to clear keyboard focus

Returns:

whether this virtual view actually cleared keyboard focus

public final void setBoundsInScreenFromBoundsInParent(AccessibilityNodeInfoCompat node, Rect boundsInParent)

Calculates and assigns screen-relative bounds based on bounds in parent. Instead of calling the deprecated AccessibilityNodeInfoCompat.setBoundsInParent(Rect), it provides a convenient method to calculate and assign AccessibilityNodeInfoCompat.setBoundsInScreen(Rect) based on boundsInParent.

Parameters:

node: The node to populate
boundsInParent: The node bounds in the viewParent's coordinates.

protected abstract int getVirtualViewAt(float x, float y)

Provides a mapping between view-relative coordinates and logical items.

Parameters:

x: The view-relative x coordinate
y: The view-relative y coordinate

Returns:

virtual view identifier for the logical item under coordinates (x,y) or ExploreByTouchHelper.HOST_ID if there is no item at the given coordinates

protected abstract void getVisibleVirtualViews(java.util.List<java.lang.Integer> virtualViewIds)

Populates a list with the view's visible items. The ordering of items within virtualViewIds specifies order of accessibility focus traversal.

Parameters:

virtualViewIds: The list to populate with visible items

protected void onPopulateEventForVirtualView(int virtualViewId, AccessibilityEvent event)

Populates an with information about the specified item.

The helper class automatically populates the following fields based on the values set by ExploreByTouchHelper.onPopulateNodeForVirtualView(int, AccessibilityNodeInfoCompat), but implementations may optionally override them:

  • event text, see
  • content description, see
  • scrollability, see
  • password state, see
  • enabled state, see
  • checked state, see

The following required fields are automatically populated by the helper class and may not be overridden:

Parameters:

virtualViewId: The virtual view id for the item for which to populate the event
event: The event to populate

protected void onPopulateEventForHost(AccessibilityEvent event)

Populates an with information about the host view.

The default implementation is a no-op.

Parameters:

event: the event to populate with information about the host view

protected abstract void onPopulateNodeForVirtualView(int virtualViewId, AccessibilityNodeInfoCompat node)

Populates an AccessibilityNodeInfoCompat with information about the specified item.

Implementations must populate the following required fields:

The helper class automatically populates the following fields with default values, but implementations may optionally override them:

The following required fields are automatically populated by the helper class and may not be overridden:

Additionally, the helper class automatically handles keyboard focus and accessibility focus management by adding the appropriate AccessibilityNodeInfoCompat.ACTION_FOCUS, AccessibilityNodeInfoCompat.ACTION_CLEAR_FOCUS, AccessibilityNodeInfoCompat.ACTION_ACCESSIBILITY_FOCUS, or AccessibilityNodeInfoCompat.ACTION_CLEAR_ACCESSIBILITY_FOCUS actions. Implementations must never manually add these actions.

The helper class also automatically modifies parent- and screen-relative bounds to reflect the portion of the item visible within its parent.

Parameters:

virtualViewId: The virtual view identifier of the item for which to populate the node
node: The node to populate

protected void onPopulateNodeForHost(AccessibilityNodeInfoCompat node)

Populates an AccessibilityNodeInfoCompat with information about the host view.

The default implementation is a no-op.

Parameters:

node: the node to populate with information about the host view

protected abstract boolean onPerformActionForVirtualView(int virtualViewId, int action, Bundle arguments)

Performs the specified accessibility action on the item associated with the virtual view identifier. See AccessibilityNodeInfoCompat.performAction(int, Bundle) for more information.

Implementations must handle any actions added manually in ExploreByTouchHelper.onPopulateNodeForVirtualView(int, AccessibilityNodeInfoCompat).

The helper class automatically handles focus management resulting from AccessibilityNodeInfoCompat.ACTION_ACCESSIBILITY_FOCUS and AccessibilityNodeInfoCompat.ACTION_CLEAR_ACCESSIBILITY_FOCUS actions.

Parameters:

virtualViewId: The virtual view identifier of the item on which to perform the action
action: The accessibility action to perform
arguments: (Optional) A bundle with additional arguments, or null

Returns:

true if the action was performed

Source

/*
 * Copyright 2018 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package androidx.customview.widget;

import android.content.Context;
import android.graphics.Rect;
import android.os.Bundle;
import android.view.KeyEvent;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewParent;
import android.view.accessibility.AccessibilityEvent;
import android.view.accessibility.AccessibilityManager;
import android.view.accessibility.AccessibilityRecord;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.collection.SparseArrayCompat;
import androidx.core.view.AccessibilityDelegateCompat;
import androidx.core.view.ViewCompat;
import androidx.core.view.ViewCompat.FocusDirection;
import androidx.core.view.ViewCompat.FocusRealDirection;
import androidx.core.view.accessibility.AccessibilityEventCompat;
import androidx.core.view.accessibility.AccessibilityNodeInfoCompat;
import androidx.core.view.accessibility.AccessibilityNodeProviderCompat;
import androidx.core.view.accessibility.AccessibilityRecordCompat;

import java.util.ArrayList;
import java.util.List;

/**
 * ExploreByTouchHelper is a utility class for implementing accessibility
 * support in custom {@link View}s that represent a collection of View-like
 * logical items. It extends {@link AccessibilityNodeProviderCompat} and
 * simplifies many aspects of providing information to accessibility services
 * and managing accessibility focus.
 * <p>
 * Clients should override abstract methods on this class and attach it to the
 * host view using {@link ViewCompat#setAccessibilityDelegate}.
 * <p>
 * The host view should also override the events in the following code snippet
 * so that the view's logical items are detected properly by the framework:
 * <p>
 * <pre>
 * class MyCustomView extends View {
 *     private MyExploreByTouchHelper mExploreByTouchHelper;
 *
 *     public MyCustomView(Context context, ...) {
 *         ...
 *         mExploreByTouchHelper = new MyExploreByTouchHelper(this);
 *         ViewCompat.setAccessibilityDelegate(this, mExploreByTouchHelper);
 *     }
 *
 *     &#64;Override
 *     public boolean dispatchHoverEvent(MotionEvent event) {
 *       return mHelper.dispatchHoverEvent(this, event)
 *           || super.dispatchHoverEvent(event);
 *     }
 *
 *     &#64;Override
 *     public boolean dispatchKeyEvent(KeyEvent event) {
 *       return mHelper.dispatchKeyEvent(event)
 *           || super.dispatchKeyEvent(event);
 *     }
 *
 *     &#64;Override
 *     public void onFocusChanged(boolean gainFocus, int direction,
 *         Rect previouslyFocusedRect) {
 *       super.onFocusChanged(gainFocus, direction, previouslyFocusedRect);
 *       mHelper.onFocusChanged(gainFocus, direction, previouslyFocusedRect);
 *     }
 * }
 * </pre>
 */
public abstract class ExploreByTouchHelper extends AccessibilityDelegateCompat {
    /** Virtual node identifier value for invalid nodes. */
    public static final int INVALID_ID = Integer.MIN_VALUE;

    /** Virtual node identifier value for the host view's node. */
    public static final int HOST_ID = View.NO_ID;

    /** Default class name used for virtual views. */
    private static final String DEFAULT_CLASS_NAME = "android.view.View";

    /** Default bounds used to determine if the client didn't set any. */
    private static final Rect INVALID_BOUNDS = new Rect(
            Integer.MAX_VALUE, Integer.MAX_VALUE, Integer.MIN_VALUE, Integer.MIN_VALUE);

    // Temporary, reusable data structures.
    private final Rect mTempScreenRect = new Rect();
    private final Rect mTempParentRect = new Rect();
    private final Rect mTempVisibleRect = new Rect();
    private final int[] mTempGlobalRect = new int[2];

    /** System accessibility manager, used to check state and send events. */
    private final AccessibilityManager mManager;

    /** View whose internal structure is exposed through this helper. */
    private final View mHost;

    /** Virtual node provider used to expose logical structure to services. */
    private MyNodeProvider mNodeProvider;

    /** Identifier for the virtual view that holds accessibility focus. */
    @SuppressWarnings("WeakerAccess") /* synthetic access */
    int mAccessibilityFocusedVirtualViewId = INVALID_ID;

    /** Identifier for the virtual view that holds keyboard focus. */
    @SuppressWarnings("WeakerAccess") /* synthetic access */
    int mKeyboardFocusedVirtualViewId = INVALID_ID;

    /** Identifier for the virtual view that is currently hovered. */
    private int mHoveredVirtualViewId = INVALID_ID;

    /**
     * Constructs a new helper that can expose a virtual view hierarchy for the
     * specified host view.
     *
     * @param host view whose virtual view hierarchy is exposed by this helper
     */
    public ExploreByTouchHelper(@NonNull View host) {
        if (host == null) {
            throw new IllegalArgumentException("View may not be null");
        }

        mHost = host;

        final Context context = host.getContext();
        mManager = (AccessibilityManager) context.getSystemService(Context.ACCESSIBILITY_SERVICE);

        // Host view must be focusable so that we can delegate to virtual
        // views.
        host.setFocusable(true);
        if (ViewCompat.getImportantForAccessibility(host)
                == ViewCompat.IMPORTANT_FOR_ACCESSIBILITY_AUTO) {
            ViewCompat.setImportantForAccessibility(
                    host, ViewCompat.IMPORTANT_FOR_ACCESSIBILITY_YES);
        }
    }

    @Override
    public AccessibilityNodeProviderCompat getAccessibilityNodeProvider(View host) {
        if (mNodeProvider == null) {
            mNodeProvider = new MyNodeProvider();
        }
        return mNodeProvider;
    }

    /**
     * Delegates hover events from the host view.
     * <p>
     * Dispatches hover {@link MotionEvent}s to the virtual view hierarchy when
     * the Explore by Touch feature is enabled.
     * <p>
     * This method should be called by overriding the host view's
     * {@link View#dispatchHoverEvent(MotionEvent)} method:
     * <pre>&#64;Override
     * public boolean dispatchHoverEvent(MotionEvent event) {
     *   return mHelper.dispatchHoverEvent(this, event)
     *       || super.dispatchHoverEvent(event);
     * }
     * </pre>
     *
     * @param event The hover event to dispatch to the virtual view hierarchy.
     * @return Whether the hover event was handled.
     */
    public final boolean dispatchHoverEvent(@NonNull MotionEvent event) {
        if (!mManager.isEnabled() || !mManager.isTouchExplorationEnabled()) {
            return false;
        }

        switch (event.getAction()) {
            case MotionEvent.ACTION_HOVER_MOVE:
            case MotionEvent.ACTION_HOVER_ENTER:
                final int virtualViewId = getVirtualViewAt(event.getX(), event.getY());
                updateHoveredVirtualView(virtualViewId);
                return (virtualViewId != INVALID_ID);
            case MotionEvent.ACTION_HOVER_EXIT:
                if (mHoveredVirtualViewId != INVALID_ID) {
                    updateHoveredVirtualView(INVALID_ID);
                    return true;
                }
                return false;
            default:
                return false;
        }
    }

    /**
     * Delegates key events from the host view.
     * <p>
     * This method should be called by overriding the host view's
     * {@link View#dispatchKeyEvent(KeyEvent)} method:
     * <pre>&#64;Override
     * public boolean dispatchKeyEvent(KeyEvent event) {
     *   return mHelper.dispatchKeyEvent(event)
     *       || super.dispatchKeyEvent(event);
     * }
     * </pre>
     */
    public final boolean dispatchKeyEvent(@NonNull KeyEvent event) {
        boolean handled = false;

        final int action = event.getAction();
        if (action != KeyEvent.ACTION_UP) {
            final int keyCode = event.getKeyCode();
            switch (keyCode) {
                case KeyEvent.KEYCODE_DPAD_LEFT:
                case KeyEvent.KEYCODE_DPAD_UP:
                case KeyEvent.KEYCODE_DPAD_RIGHT:
                case KeyEvent.KEYCODE_DPAD_DOWN:
                    if (event.hasNoModifiers()) {
                        final int direction = keyToDirection(keyCode);
                        final int count = 1 + event.getRepeatCount();
                        for (int i = 0; i < count; i++) {
                            if (moveFocus(direction, null)) {
                                handled = true;
                            } else {
                                break;
                            }
                        }
                    }
                    break;
                case KeyEvent.KEYCODE_DPAD_CENTER:
                case KeyEvent.KEYCODE_ENTER:
                    if (event.hasNoModifiers()) {
                        if (event.getRepeatCount() == 0) {
                            clickKeyboardFocusedVirtualView();
                            handled = true;
                        }
                    }
                    break;
                case KeyEvent.KEYCODE_TAB:
                    if (event.hasNoModifiers()) {
                        handled = moveFocus(View.FOCUS_FORWARD, null);
                    } else if (event.hasModifiers(KeyEvent.META_SHIFT_ON)) {
                        handled = moveFocus(View.FOCUS_BACKWARD, null);
                    }
                    break;
            }
        }

        return handled;
    }

    /**
     * Delegates focus changes from the host view.
     * <p>
     * This method should be called by overriding the host view's
     * {@link View#onFocusChanged(boolean, int, Rect)} method:
     * <pre>&#64;Override
     * public boolean onFocusChanged(boolean gainFocus, int direction,
     *     Rect previouslyFocusedRect) {
     *   super.onFocusChanged(gainFocus, direction, previouslyFocusedRect);
     *   mHelper.onFocusChanged(gainFocus, direction, previouslyFocusedRect);
     * }
     * </pre>
     */
    public final void onFocusChanged(boolean gainFocus, int direction,
            @Nullable Rect previouslyFocusedRect) {
        if (mKeyboardFocusedVirtualViewId != INVALID_ID) {
            clearKeyboardFocusForVirtualView(mKeyboardFocusedVirtualViewId);
        }

        if (gainFocus) {
            moveFocus(direction, previouslyFocusedRect);
        }
    }

    /**
     * @return the identifier of the virtual view that has accessibility focus
     *         or {@link #INVALID_ID} if no virtual view has accessibility
     *         focus
     */
    public final int getAccessibilityFocusedVirtualViewId() {
        return mAccessibilityFocusedVirtualViewId;
    }

    /**
     * @return the identifier of the virtual view that has keyboard focus
     *         or {@link #INVALID_ID} if no virtual view has keyboard focus
     */
    public final int getKeyboardFocusedVirtualViewId() {
        return mKeyboardFocusedVirtualViewId;
    }

    /**
     * Maps key event codes to focus directions.
     *
     * @param keyCode the key event code
     * @return the corresponding focus direction
     */
    @FocusRealDirection
    private static int keyToDirection(int keyCode) {
        switch (keyCode) {
            case KeyEvent.KEYCODE_DPAD_LEFT:
                return View.FOCUS_LEFT;
            case KeyEvent.KEYCODE_DPAD_UP:
                return View.FOCUS_UP;
            case KeyEvent.KEYCODE_DPAD_RIGHT:
                return View.FOCUS_RIGHT;
            default:
                return View.FOCUS_DOWN;
        }
    }

    /**
     * Obtains the bounds for the specified virtual view.
     *
     * @param virtualViewId the identifier of the virtual view
     * @param outBounds the rect to populate with virtual view bounds
     */
    private void getBoundsInScreen(int virtualViewId, Rect outBounds) {
        final AccessibilityNodeInfoCompat node = obtainAccessibilityNodeInfo(virtualViewId);
        node.getBoundsInScreen(outBounds);
    }

    /**
     * Adapts AccessibilityNodeInfoCompat for obtaining bounds.
     */
    private static final FocusStrategy.BoundsAdapter<AccessibilityNodeInfoCompat> NODE_ADAPTER =
            new FocusStrategy.BoundsAdapter<AccessibilityNodeInfoCompat>() {
                @Override
                public void obtainBounds(AccessibilityNodeInfoCompat node, Rect outBounds) {
                    node.getBoundsInScreen(outBounds);
                }
            };

    /**
     * Adapts SparseArrayCompat for iterating through values.
     */
    private static final FocusStrategy.CollectionAdapter<SparseArrayCompat<
            AccessibilityNodeInfoCompat>, AccessibilityNodeInfoCompat> SPARSE_VALUES_ADAPTER =
            new FocusStrategy.CollectionAdapter<SparseArrayCompat<
                    AccessibilityNodeInfoCompat>, AccessibilityNodeInfoCompat>() {
                @Override
                public AccessibilityNodeInfoCompat get(
                        SparseArrayCompat<AccessibilityNodeInfoCompat> collection, int index) {
                    return collection.valueAt(index);
                }

                @Override
                public int size(SparseArrayCompat<AccessibilityNodeInfoCompat> collection) {
                    return collection.size();
                }
            };

    /**
     * Attempts to move keyboard focus in the specified direction.
     *
     * @param direction the direction in which to move keyboard focus
     * @param previouslyFocusedRect the bounds of the previously focused item,
     *                              or {@code null} if not available
     * @return {@code true} if keyboard focus moved to a virtual view managed
     *         by this helper, or {@code false} otherwise
     */
    private boolean moveFocus(@FocusDirection int direction, @Nullable Rect previouslyFocusedRect) {
        final SparseArrayCompat<AccessibilityNodeInfoCompat> allNodes = getAllNodes();

        final int focusedNodeId = mKeyboardFocusedVirtualViewId;
        final AccessibilityNodeInfoCompat focusedNode =
                focusedNodeId == INVALID_ID ? null : allNodes.get(focusedNodeId);

        final AccessibilityNodeInfoCompat nextFocusedNode;
        switch (direction) {
            case View.FOCUS_FORWARD:
            case View.FOCUS_BACKWARD:
                final boolean isLayoutRtl =
                        ViewCompat.getLayoutDirection(mHost) == ViewCompat.LAYOUT_DIRECTION_RTL;
                nextFocusedNode = FocusStrategy.findNextFocusInRelativeDirection(allNodes,
                        SPARSE_VALUES_ADAPTER, NODE_ADAPTER, focusedNode, direction, isLayoutRtl,
                        false);
                break;
            case View.FOCUS_LEFT:
            case View.FOCUS_UP:
            case View.FOCUS_RIGHT:
            case View.FOCUS_DOWN:
                final Rect selectedRect = new Rect();
                if (mKeyboardFocusedVirtualViewId != INVALID_ID) {
                    // Focus is moving from a virtual view within the host.
                    getBoundsInScreen(mKeyboardFocusedVirtualViewId, selectedRect);
                } else if (previouslyFocusedRect != null) {
                    // Focus is moving from a real view outside the host.
                    selectedRect.set(previouslyFocusedRect);
                } else {
                    // Focus is moving from... somewhere? Make a guess.
                    // Usually this happens when another view was too lazy
                    // to pass the previously focused rect (ex. ScrollView
                    // when moving UP or DOWN).
                    guessPreviouslyFocusedRect(mHost, direction, selectedRect);
                }
                nextFocusedNode = FocusStrategy.findNextFocusInAbsoluteDirection(allNodes,
                        SPARSE_VALUES_ADAPTER, NODE_ADAPTER, focusedNode, selectedRect, direction);
                break;
            default:
                throw new IllegalArgumentException("direction must be one of "
                        + "{FOCUS_FORWARD, FOCUS_BACKWARD, FOCUS_UP, FOCUS_DOWN, "
                        + "FOCUS_LEFT, FOCUS_RIGHT}.");
        }

        final int nextFocusedNodeId;
        if (nextFocusedNode == null) {
            nextFocusedNodeId = INVALID_ID;
        } else {
            final int index = allNodes.indexOfValue(nextFocusedNode);
            nextFocusedNodeId = allNodes.keyAt(index);
        }

        return requestKeyboardFocusForVirtualView(nextFocusedNodeId);
    }

    private SparseArrayCompat<AccessibilityNodeInfoCompat> getAllNodes() {
        final List<Integer> virtualViewIds = new ArrayList<>();
        getVisibleVirtualViews(virtualViewIds);

        final SparseArrayCompat<AccessibilityNodeInfoCompat> allNodes = new SparseArrayCompat<>();
        for (int virtualViewIdIndex = 0; virtualViewIdIndex < virtualViewIds.size();
                virtualViewIdIndex++) {
            final AccessibilityNodeInfoCompat virtualView =
                    createNodeForChild(virtualViewIds.get(virtualViewIdIndex));
            allNodes.put(virtualViewIds.get(virtualViewIdIndex), virtualView);
        }

        return allNodes;
    }

    /**
     * Obtains a best guess for the previously focused rect for keyboard focus
     * moving in the specified direction.
     *
     * @param host the view into which focus is moving
     * @param direction the absolute direction in which focus is moving
     * @param outBounds the rect to populate with the best-guess bounds for the
     *                  previous focus rect
     */
    private static Rect guessPreviouslyFocusedRect(@NonNull View host,
            @FocusRealDirection int direction, @NonNull Rect outBounds) {
        final int w = host.getWidth();
        final int h = host.getHeight();

        switch (direction) {
            case View.FOCUS_LEFT:
                outBounds.set(w, 0, w, h);
                break;
            case View.FOCUS_UP:
                outBounds.set(0, h, w, h);
                break;
            case View.FOCUS_RIGHT:
                outBounds.set(-1, 0, -1, h);
                break;
            case View.FOCUS_DOWN:
                outBounds.set(0, -1, w, -1);
                break;
            default:
                throw new IllegalArgumentException("direction must be one of "
                        + "{FOCUS_UP, FOCUS_DOWN, FOCUS_LEFT, FOCUS_RIGHT}.");
        }

        return outBounds;
    }

    /**
     * Performs a click action on the keyboard focused virtual view, if any.
     *
     * @return {@code true} if the click action was performed successfully or
     *         {@code false} otherwise
     */
    private boolean clickKeyboardFocusedVirtualView() {
        return mKeyboardFocusedVirtualViewId != INVALID_ID && onPerformActionForVirtualView(
                mKeyboardFocusedVirtualViewId, AccessibilityNodeInfoCompat.ACTION_CLICK, null);
    }

    /**
     * Populates an event of the specified type with information about an item
     * and attempts to send it up through the view hierarchy.
     * <p>
     * You should call this method after performing a user action that normally
     * fires an accessibility event, such as clicking on an item.
     * <p>
     * <pre>public void performItemClick(T item) {
     *   ...
     *   sendEventForVirtualViewId(item.id, AccessibilityEvent.TYPE_VIEW_CLICKED);
     * }
     * </pre>
     *
     * @param virtualViewId the identifier of the virtual view for which to
     *                      send an event
     * @param eventType the type of event to send
     * @return {@code true} if the event was sent successfully, {@code false}
     *         otherwise
     */
    public final boolean sendEventForVirtualView(int virtualViewId, int eventType) {
        if ((virtualViewId == INVALID_ID) || !mManager.isEnabled()) {
            return false;
        }

        final ViewParent parent = mHost.getParent();
        if (parent == null) {
            return false;
        }

        final AccessibilityEvent event = createEvent(virtualViewId, eventType);
        return parent.requestSendAccessibilityEvent(mHost, event);
    }

    /**
     * Notifies the accessibility framework that the properties of the parent
     * view have changed.
     * <p>
     * You <strong>must</strong> call this method after adding or removing
     * items from the parent view.
     */
    public final void invalidateRoot() {
        invalidateVirtualView(HOST_ID, AccessibilityEventCompat.CONTENT_CHANGE_TYPE_SUBTREE);
    }

    /**
     * Notifies the accessibility framework that the properties of a particular
     * item have changed.
     * <p>
     * You <strong>must</strong> call this method after changing any of the
     * properties set in
     * {@link #onPopulateNodeForVirtualView(int, AccessibilityNodeInfoCompat)}.
     *
     * @param virtualViewId the virtual view id to invalidate, or
     *                      {@link #HOST_ID} to invalidate the root view
     * @see #invalidateVirtualView(int, int)
     */
    public final void invalidateVirtualView(int virtualViewId) {
        invalidateVirtualView(virtualViewId,
                AccessibilityEventCompat.CONTENT_CHANGE_TYPE_UNDEFINED);
    }

    /**
     * Notifies the accessibility framework that the properties of a particular
     * item have changed.
     * <p>
     * You <strong>must</strong> call this method after changing any of the
     * properties set in
     * {@link #onPopulateNodeForVirtualView(int, AccessibilityNodeInfoCompat)}.
     *
     * @param virtualViewId the virtual view id to invalidate, or
     *                      {@link #HOST_ID} to invalidate the root view
     * @param changeTypes the bit mask of change types. May be {@code 0} for the
     *                    default (undefined) change type or one or more of:
     *         <ul>
     *         <li>{@link AccessibilityEventCompat#CONTENT_CHANGE_TYPE_CONTENT_DESCRIPTION}
     *         <li>{@link AccessibilityEventCompat#CONTENT_CHANGE_TYPE_SUBTREE}
     *         <li>{@link AccessibilityEventCompat#CONTENT_CHANGE_TYPE_TEXT}
     *         <li>{@link AccessibilityEventCompat#CONTENT_CHANGE_TYPE_UNDEFINED}
     *         </ul>
     */
    public final void invalidateVirtualView(int virtualViewId, int changeTypes) {
        if (virtualViewId != INVALID_ID && mManager.isEnabled()) {
            final ViewParent parent = mHost.getParent();
            if (parent != null) {
                // Send events up the hierarchy so they can be coalesced.
                final AccessibilityEvent event = createEvent(virtualViewId,
                        AccessibilityEvent.TYPE_WINDOW_CONTENT_CHANGED);
                AccessibilityEventCompat.setContentChangeTypes(event, changeTypes);
                parent.requestSendAccessibilityEvent(mHost, event);
            }
        }
    }

    /**
     * Returns the virtual view ID for the currently accessibility focused
     * item.
     *
     * @return the identifier of the virtual view that has accessibility focus
     *         or {@link #INVALID_ID} if no virtual view has accessibility
     *         focus
     * @deprecated Use {@link #getAccessibilityFocusedVirtualViewId()}.
     */
    @Deprecated
    public int getFocusedVirtualView() {
        return getAccessibilityFocusedVirtualViewId();
    }

    /**
     * Called when the focus state of a virtual view changes.
     *
     * @param virtualViewId the virtual view identifier
     * @param hasFocus      {@code true} if the view has focus, {@code false}
     *                      otherwise
     */
    protected void onVirtualViewKeyboardFocusChanged(int virtualViewId, boolean hasFocus) {
        // Stub method.
    }

    /**
     * Sets the currently hovered item, sending hover accessibility events as
     * necessary to maintain the correct state.
     *
     * @param virtualViewId the virtual view id for the item currently being
     *                      hovered, or {@link #INVALID_ID} if no item is
     *                      hovered within the parent view
     */
    private void updateHoveredVirtualView(int virtualViewId) {
        if (mHoveredVirtualViewId == virtualViewId) {
            return;
        }

        final int previousVirtualViewId = mHoveredVirtualViewId;
        mHoveredVirtualViewId = virtualViewId;

        // Stay consistent with framework behavior by sending ENTER/EXIT pairs
        // in reverse order. This is accurate as of API 18.
        sendEventForVirtualView(virtualViewId, AccessibilityEvent.TYPE_VIEW_HOVER_ENTER);
        sendEventForVirtualView(
                previousVirtualViewId, AccessibilityEvent.TYPE_VIEW_HOVER_EXIT);
    }

    /**
     * Constructs and returns an {@link AccessibilityEvent} for the specified
     * virtual view id, which includes the host view ({@link #HOST_ID}).
     *
     * @param virtualViewId the virtual view id for the item for which to
     *                      construct an event
     * @param eventType the type of event to construct
     * @return an {@link AccessibilityEvent} populated with information about
     *         the specified item
     */
    private AccessibilityEvent createEvent(int virtualViewId, int eventType) {
        switch (virtualViewId) {
            case HOST_ID:
                return createEventForHost(eventType);
            default:
                return createEventForChild(virtualViewId, eventType);
        }
    }

    /**
     * Constructs and returns an {@link AccessibilityEvent} for the host node.
     *
     * @param eventType the type of event to construct
     * @return an {@link AccessibilityEvent} populated with information about
     *         the specified item
     */
    private AccessibilityEvent createEventForHost(int eventType) {
        final AccessibilityEvent event = AccessibilityEvent.obtain(eventType);
        mHost.onInitializeAccessibilityEvent(event);
        return event;
    }

    @Override
    public void onInitializeAccessibilityEvent(View host, AccessibilityEvent event) {
        super.onInitializeAccessibilityEvent(host, event);

        // Allow the client to populate the event.
        onPopulateEventForHost(event);
    }

    /**
     * Constructs and returns an {@link AccessibilityEvent} populated with
     * information about the specified item.
     *
     * @param virtualViewId the virtual view id for the item for which to
     *                      construct an event
     * @param eventType the type of event to construct
     * @return an {@link AccessibilityEvent} populated with information about
     *         the specified item
     */
    private AccessibilityEvent createEventForChild(int virtualViewId, int eventType) {
        final AccessibilityEvent event = AccessibilityEvent.obtain(eventType);
        final AccessibilityNodeInfoCompat node = obtainAccessibilityNodeInfo(virtualViewId);

        // Allow the client to override these properties,
        event.getText().add(node.getText());
        event.setContentDescription(node.getContentDescription());
        event.setScrollable(node.isScrollable());
        event.setPassword(node.isPassword());
        event.setEnabled(node.isEnabled());
        event.setChecked(node.isChecked());

        // Allow the client to populate the event.
        onPopulateEventForVirtualView(virtualViewId, event);

        // Make sure the developer is following the rules.
        if (event.getText().isEmpty() && (event.getContentDescription() == null)) {
            throw new RuntimeException("Callbacks must add text or a content description in "
                    + "populateEventForVirtualViewId()");
        }

        // Don't allow the client to override these properties.
        event.setClassName(node.getClassName());
        AccessibilityRecordCompat.setSource(event, mHost, virtualViewId);
        event.setPackageName(mHost.getContext().getPackageName());

        return event;
    }

    /**
     * Obtains a populated {@link AccessibilityNodeInfoCompat} for the
     * virtual view with the specified identifier.
     * <p>
     * This method may be called with identifier {@link #HOST_ID} to obtain a
     * node for the host view.
     *
     * @param virtualViewId the identifier of the virtual view for which to
     *                      construct a node
     * @return an {@link AccessibilityNodeInfoCompat} populated with information
     *         about the specified item
     */
    @NonNull
    AccessibilityNodeInfoCompat obtainAccessibilityNodeInfo(int virtualViewId) {
        if (virtualViewId == HOST_ID) {
            return createNodeForHost();
        }

        return createNodeForChild(virtualViewId);
    }

    /**
     * Constructs and returns an {@link AccessibilityNodeInfoCompat} for the
     * host view populated with its virtual descendants.
     *
     * @return an {@link AccessibilityNodeInfoCompat} for the parent node
     */
    @NonNull
    private AccessibilityNodeInfoCompat createNodeForHost() {
        final AccessibilityNodeInfoCompat info = AccessibilityNodeInfoCompat.obtain(mHost);
        ViewCompat.onInitializeAccessibilityNodeInfo(mHost, info);

        // Add the virtual descendants.
        final ArrayList<Integer> virtualViewIds = new ArrayList<>();
        getVisibleVirtualViews(virtualViewIds);

        final int realNodeCount = info.getChildCount();
        if (realNodeCount > 0 && virtualViewIds.size() > 0) {
            throw new RuntimeException("Views cannot have both real and virtual children");
        }

        for (int i = 0, count = virtualViewIds.size(); i < count; i++) {
            info.addChild(mHost, virtualViewIds.get(i));
        }

        return info;
    }

    @Override
    public void onInitializeAccessibilityNodeInfo(View host, AccessibilityNodeInfoCompat info) {
        super.onInitializeAccessibilityNodeInfo(host, info);

        // Allow the client to populate the host node.
        onPopulateNodeForHost(info);
    }

    /**
     * Constructs and returns an {@link AccessibilityNodeInfoCompat} for the
     * specified item. Automatically manages accessibility focus actions.
     * <p>
     * Allows the implementing class to specify most node properties, but
     * overrides the following:
     * <ul>
     * <li>{@link AccessibilityNodeInfoCompat#setPackageName}
     * <li>{@link AccessibilityNodeInfoCompat#setClassName}
     * <li>{@link AccessibilityNodeInfoCompat#setParent(View)}
     * <li>{@link AccessibilityNodeInfoCompat#setSource(View, int)}
     * <li>{@link AccessibilityNodeInfoCompat#setVisibleToUser}
     * </ul>
     *
     * @param virtualViewId the virtual view id for item for which to construct
     *                      a node
     * @return an {@link AccessibilityNodeInfoCompat} for the specified item
     */
    @NonNull
    private AccessibilityNodeInfoCompat createNodeForChild(int virtualViewId) {
        final AccessibilityNodeInfoCompat node = AccessibilityNodeInfoCompat.obtain();

        // Ensure the client has good defaults.
        node.setEnabled(true);
        node.setFocusable(true);
        node.setClassName(DEFAULT_CLASS_NAME);

        node.setBoundsInParent(INVALID_BOUNDS);
        node.setBoundsInScreen(INVALID_BOUNDS);
        node.setParent(mHost);

        // Allow the client to populate the node.
        onPopulateNodeForVirtualView(virtualViewId, node);

        // Make sure the developer is following the rules.
        if ((node.getText() == null) && (node.getContentDescription() == null)) {
            throw new RuntimeException("Callbacks must add text or a content description in "
                    + "populateNodeForVirtualViewId()");
        }

        node.getBoundsInParent(mTempParentRect);
        node.getBoundsInScreen(mTempScreenRect);
        if (mTempParentRect.equals(INVALID_BOUNDS) && mTempScreenRect.equals(
                INVALID_BOUNDS)) {
            throw new RuntimeException("Callbacks must set parent bounds or screen bounds in "
                    + "populateNodeForVirtualViewId()");
        }

        final int actions = node.getActions();
        if ((actions & AccessibilityNodeInfoCompat.ACTION_ACCESSIBILITY_FOCUS) != 0) {
            throw new RuntimeException("Callbacks must not add ACTION_ACCESSIBILITY_FOCUS in "
                    + "populateNodeForVirtualViewId()");
        }
        if ((actions & AccessibilityNodeInfoCompat.ACTION_CLEAR_ACCESSIBILITY_FOCUS) != 0) {
            throw new RuntimeException("Callbacks must not add ACTION_CLEAR_ACCESSIBILITY_FOCUS in "
                    + "populateNodeForVirtualViewId()");
        }

        // Don't allow the client to override these properties.
        node.setPackageName(mHost.getContext().getPackageName());
        node.setSource(mHost, virtualViewId);

        // Manage internal accessibility focus state.
        if (mAccessibilityFocusedVirtualViewId == virtualViewId) {
            node.setAccessibilityFocused(true);
            node.addAction(AccessibilityNodeInfoCompat.ACTION_CLEAR_ACCESSIBILITY_FOCUS);
        } else {
            node.setAccessibilityFocused(false);
            node.addAction(AccessibilityNodeInfoCompat.ACTION_ACCESSIBILITY_FOCUS);
        }

        // Manage internal keyboard focus state.
        final boolean isFocused = mKeyboardFocusedVirtualViewId == virtualViewId;
        if (isFocused) {
            node.addAction(AccessibilityNodeInfoCompat.ACTION_CLEAR_FOCUS);
        } else if (node.isFocusable()) {
            node.addAction(AccessibilityNodeInfoCompat.ACTION_FOCUS);
        }
        node.setFocused(isFocused);

        mHost.getLocationOnScreen(mTempGlobalRect);

        if (mTempScreenRect.equals(INVALID_BOUNDS)) {
            setBoundsInScreenFromBoundsInParent(node, mTempParentRect);
            node.getBoundsInScreen(mTempScreenRect);
        }

        if (mHost.getLocalVisibleRect(mTempVisibleRect)) {
            mTempVisibleRect.offset(mTempGlobalRect[0] - mHost.getScrollX(),
                    mTempGlobalRect[1] - mHost.getScrollY());
            final boolean intersects = mTempScreenRect.intersect(mTempVisibleRect);
            if (intersects) {
                node.setBoundsInScreen(mTempScreenRect);
                if (isVisibleToUser(mTempScreenRect)) {
                    node.setVisibleToUser(true);
                }
            }
        }

        return node;
    }

    boolean performAction(int virtualViewId, int action, Bundle arguments) {
        switch (virtualViewId) {
            case HOST_ID:
                return performActionForHost(action, arguments);
            default:
                return performActionForChild(virtualViewId, action, arguments);
        }
    }

    private boolean performActionForHost(int action, Bundle arguments) {
        return ViewCompat.performAccessibilityAction(mHost, action, arguments);
    }

    private boolean performActionForChild(int virtualViewId, int action, Bundle arguments) {
        switch (action) {
            case AccessibilityNodeInfoCompat.ACTION_ACCESSIBILITY_FOCUS:
                return requestAccessibilityFocus(virtualViewId);
            case AccessibilityNodeInfoCompat.ACTION_CLEAR_ACCESSIBILITY_FOCUS:
                return clearAccessibilityFocus(virtualViewId);
            case AccessibilityNodeInfoCompat.ACTION_FOCUS:
                return requestKeyboardFocusForVirtualView(virtualViewId);
            case AccessibilityNodeInfoCompat.ACTION_CLEAR_FOCUS:
                return clearKeyboardFocusForVirtualView(virtualViewId);
            default:
                return onPerformActionForVirtualView(virtualViewId, action, arguments);
        }
    }

    /**
     * Computes whether the specified {@link Rect} intersects with the visible
     * portion of its parent {@link View}. Modifies {@code screenRect} to contain
     * only the visible portion.
     *
     * @param screenRect a rectangle in screen coordinates
     * @return whether the specified {@link Rect} is visible on the screen
     */
    private boolean isVisibleToUser(Rect screenRect) {
        // Missing or empty bounds mean this view is not visible.
        if ((screenRect == null) || screenRect.isEmpty()) {
            return false;
        }

        // Attached to invisible window means this view is not visible.
        if (mHost.getWindowVisibility() != View.VISIBLE) {
            return false;
        }

        // An invisible predecessor means that this view is not visible.
        ViewParent viewParent = mHost.getParent();
        while (viewParent instanceof View) {
            final View view = (View) viewParent;
            if ((view.getAlpha() <= 0) || (view.getVisibility() != View.VISIBLE)) {
                return false;
            }
            viewParent = view.getParent();
        }

        // A null parent implies the view is not visible.
        return viewParent != null;
    }

    /**
     * Attempts to give accessibility focus to a virtual view.
     * <p>
     * A virtual view will not actually take focus if
     * {@link AccessibilityManager#isEnabled()} returns false,
     * {@link AccessibilityManager#isTouchExplorationEnabled()} returns false,
     * or the view already has accessibility focus.
     *
     * @param virtualViewId the identifier of the virtual view on which to
     *                      place accessibility focus
     * @return whether this virtual view actually took accessibility focus
     */
    private boolean requestAccessibilityFocus(int virtualViewId) {
        if (!mManager.isEnabled() || !mManager.isTouchExplorationEnabled()) {
            return false;
        }
        // TODO: Check virtual view visibility.
        if (mAccessibilityFocusedVirtualViewId != virtualViewId) {
            // Clear focus from the previously focused view, if applicable.
            if (mAccessibilityFocusedVirtualViewId != INVALID_ID) {
                clearAccessibilityFocus(mAccessibilityFocusedVirtualViewId);
            }

            // Set focus on the new view.
            mAccessibilityFocusedVirtualViewId = virtualViewId;

            // TODO: Only invalidate virtual view bounds.
            mHost.invalidate();
            sendEventForVirtualView(virtualViewId,
                    AccessibilityEventCompat.TYPE_VIEW_ACCESSIBILITY_FOCUSED);
            return true;
        }
        return false;
    }

    /**
     * Attempts to clear accessibility focus from a virtual view.
     *
     * @param virtualViewId the identifier of the virtual view from which to
     *                      clear accessibility focus
     * @return whether this virtual view actually cleared accessibility focus
     */
    private boolean clearAccessibilityFocus(int virtualViewId) {
        if (mAccessibilityFocusedVirtualViewId == virtualViewId) {
            mAccessibilityFocusedVirtualViewId = INVALID_ID;
            mHost.invalidate();
            sendEventForVirtualView(virtualViewId,
                    AccessibilityEventCompat.TYPE_VIEW_ACCESSIBILITY_FOCUS_CLEARED);
            return true;
        }
        return false;
    }

    /**
     * Attempts to give keyboard focus to a virtual view.
     *
     * @param virtualViewId the identifier of the virtual view on which to
     *                      place keyboard focus
     * @return whether this virtual view actually took keyboard focus
     */
    public final boolean requestKeyboardFocusForVirtualView(int virtualViewId) {
        if (!mHost.isFocused() && !mHost.requestFocus()) {
            // Host must have real keyboard focus.
            return false;
        }

        if (mKeyboardFocusedVirtualViewId == virtualViewId) {
            // The virtual view already has focus.
            return false;
        }

        if (mKeyboardFocusedVirtualViewId != INVALID_ID) {
            clearKeyboardFocusForVirtualView(mKeyboardFocusedVirtualViewId);
        }

        if (virtualViewId == INVALID_ID) {
            return false;
        }

        mKeyboardFocusedVirtualViewId = virtualViewId;

        onVirtualViewKeyboardFocusChanged(virtualViewId, true);
        sendEventForVirtualView(virtualViewId, AccessibilityEvent.TYPE_VIEW_FOCUSED);

        return true;
    }

    /**
     * Attempts to clear keyboard focus from a virtual view.
     *
     * @param virtualViewId the identifier of the virtual view from which to
     *                      clear keyboard focus
     * @return whether this virtual view actually cleared keyboard focus
     */
    public final boolean clearKeyboardFocusForVirtualView(int virtualViewId) {
        if (mKeyboardFocusedVirtualViewId != virtualViewId) {
            // The virtual view is not focused.
            return false;
        }

        mKeyboardFocusedVirtualViewId = INVALID_ID;

        onVirtualViewKeyboardFocusChanged(virtualViewId, false);
        sendEventForVirtualView(virtualViewId, AccessibilityEvent.TYPE_VIEW_FOCUSED);

        return true;
    }

    /**
     * Calculates and assigns screen-relative bounds based on bounds in parent. Instead
     * of calling the deprecated {@link AccessibilityNodeInfoCompat#setBoundsInParent(Rect)}, it
     * provides a convenient method to calculate and assign
     * {@link AccessibilityNodeInfoCompat#setBoundsInScreen(Rect)} based on {@code boundsInParent}.
     *
     * @param node The node to populate
     * @param boundsInParent The node bounds in the viewParent's coordinates.
     */
    public final void setBoundsInScreenFromBoundsInParent(@NonNull AccessibilityNodeInfoCompat node,
            @NonNull Rect boundsInParent) {
        node.setBoundsInParent(boundsInParent);
        Rect screenRect = new Rect();
        screenRect.set(boundsInParent);

        // If there is a parent node, adjust bounds based on the parent node.
        if (node.mParentVirtualDescendantId != HOST_ID) {
            AccessibilityNodeInfoCompat parentNode = AccessibilityNodeInfoCompat.obtain();
            Rect tempParentRect = new Rect();
            // Walk up the node tree to adjust the screen rect.
            for (int virtualDescendantId = node.mParentVirtualDescendantId;
                    virtualDescendantId != HOST_ID;
                    virtualDescendantId = parentNode.mParentVirtualDescendantId) {
                // Reset the values in the parent node we'll be using.
                parentNode.setParent(mHost, HOST_ID);
                parentNode.setBoundsInParent(INVALID_BOUNDS);
                // Adjust the bounds for the parent node.
                onPopulateNodeForVirtualView(virtualDescendantId, parentNode);
                parentNode.getBoundsInParent(tempParentRect);
                screenRect.offset(tempParentRect.left, tempParentRect.top);
            }
            parentNode.recycle();
        }
        // Adjust the rect for the host view's location.
        mHost.getLocationOnScreen(mTempGlobalRect);
        screenRect.offset(mTempGlobalRect[0] - mHost.getScrollX(),
                mTempGlobalRect[1] - mHost.getScrollY());
        node.setBoundsInScreen(screenRect);
    }

    /**
     * Provides a mapping between view-relative coordinates and logical
     * items.
     *
     * @param x The view-relative x coordinate
     * @param y The view-relative y coordinate
     * @return virtual view identifier for the logical item under
     *         coordinates (x,y) or {@link #HOST_ID} if there is no item at
     *         the given coordinates
     */
    protected abstract int getVirtualViewAt(float x, float y);

    /**
     * Populates a list with the view's visible items. The ordering of items
     * within {@code virtualViewIds} specifies order of accessibility focus
     * traversal.
     *
     * @param virtualViewIds The list to populate with visible items
     */
    protected abstract void getVisibleVirtualViews(List<Integer> virtualViewIds);

    /**
     * Populates an {@link AccessibilityEvent} with information about the
     * specified item.
     * <p>
     * The helper class automatically populates the following fields based on
     * the values set by
     * {@link #onPopulateNodeForVirtualView(int, AccessibilityNodeInfoCompat)},
     * but implementations may optionally override them:
     * <ul>
     * <li>event text, see {@link AccessibilityEvent#getText()}
     * <li>content description, see
     * {@link AccessibilityEvent#setContentDescription(CharSequence)}
     * <li>scrollability, see {@link AccessibilityEvent#setScrollable(boolean)}
     * <li>password state, see {@link AccessibilityEvent#setPassword(boolean)}
     * <li>enabled state, see {@link AccessibilityEvent#setEnabled(boolean)}
     * <li>checked state, see {@link AccessibilityEvent#setChecked(boolean)}
     * </ul>
     * <p>
     * The following required fields are automatically populated by the
     * helper class and may not be overridden:
     * <ul>
     * <li>item class name, set to the value used in
     * {@link #onPopulateNodeForVirtualView(int, AccessibilityNodeInfoCompat)}
     * <li>package name, set to the package of the host view's
     * {@link Context}, see {@link AccessibilityEvent#setPackageName}
     * <li>event source, set to the host view and virtual view identifier,
     * see {@link AccessibilityRecordCompat#setSource(AccessibilityRecord, View, int)}
     * </ul>
     *
     * @param virtualViewId The virtual view id for the item for which to
     *            populate the event
     * @param event The event to populate
     */
    protected void onPopulateEventForVirtualView(int virtualViewId,
            @NonNull AccessibilityEvent event) {
        // Default implementation is no-op.
    }

    /**
     * Populates an {@link AccessibilityEvent} with information about the host
     * view.
     * <p>
     * The default implementation is a no-op.
     *
     * @param event the event to populate with information about the host view
     */
    protected void onPopulateEventForHost(@NonNull AccessibilityEvent event) {
        // Default implementation is no-op.
    }

    /**
     * Populates an {@link AccessibilityNodeInfoCompat} with information
     * about the specified item.
     * <p>
     * Implementations <strong>must</strong> populate the following required
     * fields:
     * <ul>
     * <li>event text, see
     * {@link AccessibilityNodeInfoCompat#setText(CharSequence)} or
     * {@link AccessibilityNodeInfoCompat#setContentDescription(CharSequence)}
     * <li>bounds in screen coordinates, see
     * {@link AccessibilityNodeInfoCompat#setBoundsInScreen(Rect)} and
     * {@link ExploreByTouchHelper#setBoundsInScreenFromBoundsInParent
     * (AccessibilityNodeInfoCompat, Rect)}
     * </ul>
     * <p>
     * The helper class automatically populates the following fields with
     * default values, but implementations may optionally override them:
     * <ul>
     * <li>enabled state, set to {@code true}, see
     * {@link AccessibilityNodeInfoCompat#setEnabled(boolean)}
     * <li>keyboard focusability, set to {@code true}, see
     * {@link AccessibilityNodeInfoCompat#setFocusable(boolean)}
     * <li>item class name, set to {@code android.view.View}, see
     * {@link AccessibilityNodeInfoCompat#setClassName(CharSequence)}
     * </ul>
     * <p>
     * The following required fields are automatically populated by the
     * helper class and may not be overridden:
     * <ul>
     * <li>package name, identical to the package name set by
     * {@link #onPopulateEventForVirtualView(int, AccessibilityEvent)}, see
     * {@link AccessibilityNodeInfoCompat#setPackageName}
     * <li>node source, identical to the event source set in
     * {@link #onPopulateEventForVirtualView(int, AccessibilityEvent)}, see
     * {@link AccessibilityNodeInfoCompat#setSource(View, int)}
     * <li>parent view, set to the host view, see
     * {@link AccessibilityNodeInfoCompat#setParent(View)}
     * <li>visibility, computed based on parent-relative bounds, see
     * {@link AccessibilityNodeInfoCompat#setVisibleToUser(boolean)}
     * <li>accessibility focus, computed based on internal helper state, see
     * {@link AccessibilityNodeInfoCompat#setAccessibilityFocused(boolean)}
     * <li>keyboard focus, computed based on internal helper state, see
     * {@link AccessibilityNodeInfoCompat#setFocused(boolean)}
     * </ul>
     * <p>
     * Additionally, the helper class automatically handles keyboard focus and
     * accessibility focus management by adding the appropriate
     * {@link AccessibilityNodeInfoCompat#ACTION_FOCUS},
     * {@link AccessibilityNodeInfoCompat#ACTION_CLEAR_FOCUS},
     * {@link AccessibilityNodeInfoCompat#ACTION_ACCESSIBILITY_FOCUS}, or
     * {@link AccessibilityNodeInfoCompat#ACTION_CLEAR_ACCESSIBILITY_FOCUS}
     * actions. Implementations must <strong>never</strong> manually add these
     * actions.
     * <p>
     * The helper class also automatically modifies parent- and
     * screen-relative bounds to reflect the portion of the item visible
     * within its parent.
     *
     * @param virtualViewId The virtual view identifier of the item for
     *            which to populate the node
     * @param node The node to populate
     */
    protected abstract void onPopulateNodeForVirtualView(
            int virtualViewId, @NonNull AccessibilityNodeInfoCompat node);

    /**
     * Populates an {@link AccessibilityNodeInfoCompat} with information
     * about the host view.
     * <p>
     * The default implementation is a no-op.
     *
     * @param node the node to populate with information about the host view
     */
    protected void onPopulateNodeForHost(@NonNull AccessibilityNodeInfoCompat node) {
        // Default implementation is no-op.
    }

    /**
     * Performs the specified accessibility action on the item associated
     * with the virtual view identifier. See
     * {@link AccessibilityNodeInfoCompat#performAction(int, Bundle)} for
     * more information.
     * <p>
     * Implementations <strong>must</strong> handle any actions added manually
     * in
     * {@link #onPopulateNodeForVirtualView(int, AccessibilityNodeInfoCompat)}.
     * <p>
     * The helper class automatically handles focus management resulting
     * from {@link AccessibilityNodeInfoCompat#ACTION_ACCESSIBILITY_FOCUS}
     * and
     * {@link AccessibilityNodeInfoCompat#ACTION_CLEAR_ACCESSIBILITY_FOCUS}
     * actions.
     *
     * @param virtualViewId The virtual view identifier of the item on which
     *            to perform the action
     * @param action The accessibility action to perform
     * @param arguments (Optional) A bundle with additional arguments, or
     *            null
     * @return true if the action was performed
     */
    protected abstract boolean onPerformActionForVirtualView(
            int virtualViewId, int action, @Nullable Bundle arguments);

    /**
     * Exposes a virtual view hierarchy to the accessibility framework.
     */
    private class MyNodeProvider extends AccessibilityNodeProviderCompat {
        MyNodeProvider() {
        }

        @Override
        public AccessibilityNodeInfoCompat createAccessibilityNodeInfo(int virtualViewId) {
            // The caller takes ownership of the node and is expected to
            // recycle it when done, so always return a copy.
            final AccessibilityNodeInfoCompat node =
                    ExploreByTouchHelper.this.obtainAccessibilityNodeInfo(virtualViewId);
            return AccessibilityNodeInfoCompat.obtain(node);
        }

        @Override
        public boolean performAction(int virtualViewId, int action, Bundle arguments) {
            return ExploreByTouchHelper.this.performAction(virtualViewId, action, arguments);
        }

        @Override
        public AccessibilityNodeInfoCompat findFocus(int focusType) {
            int focusedId = (focusType == AccessibilityNodeInfoCompat.FOCUS_ACCESSIBILITY)
                    ? mAccessibilityFocusedVirtualViewId : mKeyboardFocusedVirtualViewId;
            if (focusedId == INVALID_ID) {
                return null;
            }
            return createAccessibilityNodeInfo(focusedId);
        }
    }
}