ExploreByTouchHelper

public abstract class ExploreByTouchHelper
extends AccessibilityDelegateCompat

java.lang.Object
   ↳ androidx.core.view.AccessibilityDelegateCompat
     ↳ androidx.customview.widget.ExploreByTouchHelper


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

Constants

int HOST_ID

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

int INVALID_ID

Virtual node identifier value for invalid nodes.

Public constructors

ExploreByTouchHelper(View host)

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

Public methods

final boolean clearKeyboardFocusForVirtualView(int virtualViewId)

Attempts to clear keyboard focus from a virtual view.

final boolean dispatchHoverEvent(MotionEvent event)

Delegates hover events from the host view.

final boolean dispatchKeyEvent(KeyEvent event)

Delegates key events from the host view.

final int getAccessibilityFocusedVirtualViewId()
AccessibilityNodeProviderCompat getAccessibilityNodeProvider(View host)

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

int getFocusedVirtualView()

This method is deprecated. Use getAccessibilityFocusedVirtualViewId().

final int getKeyboardFocusedVirtualViewId()
final void invalidateRoot()

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

final void invalidateVirtualView(int virtualViewId)

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

final void invalidateVirtualView(int virtualViewId, int changeTypes)

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

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

Delegates focus changes from the host view.

void onInitializeAccessibilityEvent(View host, AccessibilityEvent event)

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

void onInitializeAccessibilityNodeInfo(View host, AccessibilityNodeInfoCompat info)

Initializes an AccessibilityNodeInfoCompat with information about the host view.

final boolean requestKeyboardFocusForVirtualView(int virtualViewId)

Attempts to give keyboard focus to a virtual view.

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.

Protected methods

abstract int getVirtualViewAt(float x, float y)

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

abstract void getVisibleVirtualViews(List<Integer> virtualViewIds)

Populates a list with the view's visible items.

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

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

void onPopulateEventForHost(AccessibilityEvent event)

Populates an AccessibilityEvent with information about the host view.

void onPopulateEventForVirtualView(int virtualViewId, AccessibilityEvent event)

Populates an AccessibilityEvent with information about the specified item.

void onPopulateNodeForHost(AccessibilityNodeInfoCompat node)

Populates an AccessibilityNodeInfoCompat with information about the host view.

abstract void onPopulateNodeForVirtualView(int virtualViewId, AccessibilityNodeInfoCompat node)

Populates an AccessibilityNodeInfoCompat with information about the specified item.

void onVirtualViewKeyboardFocusChanged(int virtualViewId, boolean hasFocus)

Called when the focus state of a virtual view changes.

Inherited methods

Constants

HOST_ID

public static final int HOST_ID

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

Constant Value: -1 (0xffffffff)

INVALID_ID

public static final int INVALID_ID

Virtual node identifier value for invalid nodes.

Constant Value: -2147483648 (0x80000000)

Public constructors

ExploreByTouchHelper

public ExploreByTouchHelper (View host)

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

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

Public methods

clearKeyboardFocusForVirtualView

public final boolean clearKeyboardFocusForVirtualView (int virtualViewId)

Attempts to clear keyboard focus from a virtual view.

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

Returns
boolean whether this virtual view actually cleared keyboard focus

dispatchHoverEvent

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.dispatchHoverEvent(MotionEvent) method:

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

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

Returns
boolean Whether the hover event was handled.

dispatchKeyEvent

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.dispatchKeyEvent(KeyEvent) method:

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

Parameters
event KeyEvent

Returns
boolean

getAccessibilityFocusedVirtualViewId

public final int getAccessibilityFocusedVirtualViewId ()

Returns
int the identifier of the virtual view that has accessibility focus or INVALID_ID if no virtual view has accessibility focus

getAccessibilityNodeProvider

public AccessibilityNodeProviderCompat getAccessibilityNodeProvider (View host)

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

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

Parameters
host View

Returns
AccessibilityNodeProviderCompat The provider.

getFocusedVirtualView

public int getFocusedVirtualView ()

This method is deprecated.
Use getAccessibilityFocusedVirtualViewId().

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

Returns
int the identifier of the virtual view that has accessibility focus or INVALID_ID if no virtual view has accessibility focus

getKeyboardFocusedVirtualViewId

public final int getKeyboardFocusedVirtualViewId ()

Returns
int the identifier of the virtual view that has keyboard focus or INVALID_ID if no virtual view has keyboard focus

invalidateRoot

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.

invalidateVirtualView

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 onPopulateNodeForVirtualView(int, AccessibilityNodeInfoCompat).

Parameters
virtualViewId int: the virtual view id to invalidate, or HOST_ID to invalidate the root view

invalidateVirtualView

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 onPopulateNodeForVirtualView(int, AccessibilityNodeInfoCompat).

Parameters
virtualViewId int: the virtual view id to invalidate, or HOST_ID to invalidate the root view

changeTypes int: the bit mask of change types. May be 0 for the default (undefined) change type or one or more of:

onFocusChanged

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.onFocusChanged(boolean, int, Rect) method:

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

Parameters
gainFocus boolean

direction int

previouslyFocusedRect Rect

onInitializeAccessibilityEvent

public void onInitializeAccessibilityEvent (View host, 
                AccessibilityEvent event)

Initializes an AccessibilityEvent 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 View: The View hosting the delegate.

event AccessibilityEvent: The event to initialize.

onInitializeAccessibilityNodeInfo

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 View: The View hosting the delegate.

info AccessibilityNodeInfoCompat: The instance to initialize.

requestKeyboardFocusForVirtualView

public final boolean requestKeyboardFocusForVirtualView (int virtualViewId)

Attempts to give keyboard focus to a virtual view.

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

Returns
boolean whether this virtual view actually took keyboard focus

sendEventForVirtualView

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 int: the identifier of the virtual view for which to send an event

eventT