Android APIs
public abstract class

ExploreByTouchHelper

extends AccessibilityDelegateCompat
java.lang.Object
   ↳ android.support.v4.view.AccessibilityDelegateCompat
     ↳ android.support.v4.widget.ExploreByTouchHelper

Class 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. This class does not currently support hierarchies of logical items.

This should be applied to the parent view using setAccessibilityDelegate(View, AccessibilityDelegateCompat): 

 mAccessHelper = ExploreByTouchHelper.create(someView, mAccessHelperCallback);
 ViewCompat.setAccessibilityDelegate(someView, mAccessHelper);

Summary

Constants
int INVALID_ID Virtual node identifier value for invalid nodes.
Public Constructors
ExploreByTouchHelper(View forView)
Factory method to create a new ExploreByTouchHelper.
Public Methods
boolean dispatchHoverEvent(MotionEvent event)
Dispatches hover MotionEvents to the virtual view hierarchy when the Explore by Touch feature is enabled.
AccessibilityNodeProviderCompat getAccessibilityNodeProvider(View host)
Returns the AccessibilityNodeProviderCompat for this helper.
int getFocusedVirtualView()
Returns the virtual view id for the currently focused item,
void invalidateRoot()
Notifies the accessibility framework that the properties of the parent view have changed.
void invalidateVirtualView(int virtualViewId)
Notifies the accessibility framework that the properties of a particular item have changed.
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.
abstract void onPopulateEventForVirtualView(int virtualViewId, AccessibilityEvent event)
Populates an AccessibilityEvent with information about the specified item.
abstract void onPopulateNodeForVirtualView(int virtualViewId, AccessibilityNodeInfoCompat node)
Populates an AccessibilityNodeInfoCompat with information about the specified item.
[Expand]
Inherited Methods
From class android.support.v4.view.AccessibilityDelegateCompat
From class java.lang.Object

Constants

public static final int INVALID_ID

Virtual node identifier value for invalid nodes.

Constant Value: -2147483648 (0x80000000)

Public Constructors

public ExploreByTouchHelper (View forView)

Factory method to create a new ExploreByTouchHelper.

Parameters
forView View whose logical children are exposed by this helper.

Public Methods

public boolean dispatchHoverEvent (MotionEvent event)

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

This method should be called by overriding dispatchHoverEvent(MotionEvent): 

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

Parameters
event The hover event to dispatch to the virtual view hierarchy.
Returns
  • Whether the hover event was handled.

public AccessibilityNodeProviderCompat getAccessibilityNodeProvider (View host)

Returns the AccessibilityNodeProviderCompat for this helper.

Parameters
host View whose logical children are exposed by this helper.
Returns
  • The accessibility node provider for this helper.

public int getFocusedVirtualView ()

Returns the virtual view id for the currently focused item,

Returns
  • A virtual view id, or INVALID_ID if no item is currently focused.

public 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 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 The virtual view id to invalidate.

public 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 virtual view id for which to send an event.
eventType The type of event to send.
Returns
  • true if the event was sent successfully.

Protected Methods

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 NO_ID if there is no item at the given coordinates

protected abstract void getVisibleVirtualViews (List<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 abstract boolean onPerformActionForVirtualView (int virtualViewId, int action, Bundle arguments)

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

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

The helper class automatically handles focus management resulting from ACTION_ACCESSIBILITY_FOCUS and 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

protected abstract void onPopulateEventForVirtualView (int virtualViewId, AccessibilityEvent event)

Populates an AccessibilityEvent 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:

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

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 accessibility focus management by adding the appropriate ACTION_ACCESSIBILITY_FOCUS or ACTION_CLEAR_ACCESSIBILITY_FOCUS action. 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