ExploreByTouchHelper

public abstract class ExploreByTouchHelper extends AccessibilityDelegateCompat


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 setAccessibilityDelegate.

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

static final int
HOST_ID = -1

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

static final int
INVALID_ID = -2147483648

Virtual node identifier value for invalid nodes.

Public constructors

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

Public methods

final boolean

Attempts to clear keyboard focus from a virtual view.

final boolean

Delegates hover events from the host view.

final boolean

Delegates key events from the host view.

final int
AccessibilityNodeProviderCompat

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

int

This method is deprecated.

Use getAccessibilityFocusedVirtualViewId.

final int
final void

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,
    @Nullable Rect previouslyFocusedRect
)

Delegates focus changes from the host view.

void

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

void

Initializes an AccessibilityNodeInfoCompat with information about the host view.

final boolean

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.

final void

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

Protected methods

abstract int
getVirtualViewAt(float x, float y)

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

abstract void

Populates a list with the view's visible items.

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

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

void

Populates an AccessibilityEvent with information about the host view.

void
onPopulateEventForVirtualView(
    int virtualViewId,
    @NonNull AccessibilityEvent event
)

Populates an AccessibilityEvent with information about the specified item.

void

Populates an AccessibilityNodeInfoCompat with information about the host view.

abstract void
onPopulateNodeForVirtualView(
    int virtualViewId,
    @NonNull 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

From androidx.core.view.AccessibilityDelegateCompat
boolean

Dispatches an AccessibilityEvent to the host View first and then to its children for adding their text content to the event.

void

Gives a chance to the host View to populate the accessibility event with its text content.

boolean

Called when a child of the host View has requested sending an AccessibilityEvent and gives an opportunity to the parent (the host) to augment the event.

boolean
performAccessibilityAction(
    @NonNull View host,
    int action,
    @Nullable Bundle args
)

Performs the specified accessibility action on the view.

void
sendAccessibilityEvent(@NonNull View host, int eventType)

Sends an accessibility event of the given type.

void

Sends an accessibility event.

Constants

HOST_ID

Added in 1.0.0
public static final int HOST_ID = -1

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

INVALID_ID

Added in 1.0.0
public static final int INVALID_ID = -2147483648

Virtual node identifier value for invalid nodes.

Public constructors

ExploreByTouchHelper

Added in 1.0.0
public ExploreByTouchHelper(@NonNull View host)

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

Parameters
@NonNull View host

view whose virtual view hierarchy is exposed by this helper

Public methods

clearKeyboardFocusForVirtualView

Added in 1.0.0
public final boolean clearKeyboardFocusForVirtualView(int virtualViewId)

Attempts to clear keyboard focus from a virtual view.

Parameters
int virtualViewId

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

Returns
boolean

whether this virtual view actually cleared keyboard focus

dispatchHoverEvent

Added in 1.0.0
public final boolean dispatchHoverEvent(@NonNull 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 dispatchHoverEvent method:

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

The hover event to dispatch to the virtual view hierarchy.

Returns
boolean

Whether the hover event was handled.

dispatchKeyEvent

Added in 1.0.0
public final boolean dispatchKeyEvent(@NonNull KeyEvent event)

Delegates key events from the host view.

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

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

getAccessibilityFocusedVirtualViewId

Added in 1.0.0
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.

Returns
AccessibilityNodeProviderCompat

The provider.

getFocusedVirtualView

Added in 1.0.0
Deprecated in 1.0.0
public int getFocusedVirtualView()

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

Added in 1.0.0
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

Added in 1.0.0
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

Added in 1.0.0
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.

Parameters
int virtualViewId

the virtual view id to invalidate, or HOST_ID to invalidate the root view

invalidateVirtualView

Added in 1.0.0
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.

Parameters
int virtualViewId

the virtual view id to invalidate, or HOST_ID to invalidate the root view

int changeTypes

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

onFocusChanged

Added in 1.0.0
public final void onFocusChanged(
    boolean gainFocus,
    int direction,
    @Nullable Rect previouslyFocusedRect
)

Delegates focus changes from the host view.

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

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

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
View host

The View hosting the delegate.

AccessibilityEvent event

The event to initialize.

See also
onInitializeAccessibilityEvent

ViewCompat#onInitializeAccessibilityEvent(View, AccessibilityEvent)

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
View host

The View hosting the delegate.

AccessibilityNodeInfoCompat info

The instance to initialize.

See also
onInitializeAccessibilityNodeInfo

ViewCompat#onInitializeAccessibilityNodeInfo(View, AccessibilityNodeInfoCompat)

requestKeyboardFocusForVirtualView

Added in 1.0.0
public final boolean requestKeyboardFocusForVirtualView(int virtualViewId)

Attempts to give keyboard focus to a virtual view.

Parameters
int virtualViewId

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

Returns
boolean

whether this virtual view actually took keyboard focus

sendEventForVirtualView

Added in 1.0.0
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
int virtualViewId

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

int eventType

the type of event to send

Returns
boolean

true if the event was sent successfully, false otherwise

setBoundsInScreenFromBoundsInParent

Added in 1.2.0-alpha03
public final void setBoundsInScreenFromBoundsInParent(
    @NonNull AccessibilityNodeInfoCompat node,
    @NonNull Rect boundsInParent
)

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

Parameters
@NonNull AccessibilityNodeInfoCompat node

The node to populate

@NonNull Rect boundsInParent

The node bounds in the viewParent's coordinates.

Protected methods

getVirtualViewAt

Added in 1.0.0
protected abstract int getVirtualViewAt(float x, float y)

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

Parameters
float x

The view-relative x coordinate

float y

The view-relative y coordinate

Returns
int

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

getVisibleVirtualViews

Added in 1.0.0
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
List<Integer> virtualViewIds

The list to populate with visible items

onPerformActionForVirtualView

Added in 1.0.0
protected abstract boolean onPerformActionForVirtualView(
    int virtualViewId,
    int action,
    @Nullable Bundle arguments
)

Performs the specified accessibility action on the item associated with the virtual view identifier. See performAction for more information.

Implementations must handle any actions added manually in onPopulateNodeForVirtualView.

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

Parameters
int virtualViewId

The virtual view identifier of the item on which to perform the action

int action

The accessibility action to perform

@Nullable Bundle arguments

(Optional) A bundle with additional arguments, or null

Returns
boolean

true if the action was performed

onPopulateEventForHost

Added in 1.0.0
protected void onPopulateEventForHost(@NonNull AccessibilityEvent event)

Populates an AccessibilityEvent with information about the host view.

The default implementation is a no-op.

Parameters
@NonNull AccessibilityEvent event

the event to populate with information about the host view

onPopulateEventForVirtualView

Added in 1.0.0
protected void onPopulateEventForVirtualView(
    int virtualViewId,
    @NonNull AccessibilityEvent event
)

Populates an AccessibilityEvent with information about the specified item.

The helper class automatically populates the following fields based on the values set by onPopulateNodeForVirtualView, but implementations may optionally override them:

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

Parameters
int virtualViewId

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

@NonNull AccessibilityEvent event

The event to populate

onPopulateNodeForHost

Added in 1.0.0
protected void onPopulateNodeForHost(@NonNull AccessibilityNodeInfoCompat node)

Populates an AccessibilityNodeInfoCompat with information about the host view.

The default implementation is a no-op.

Parameters
@NonNull AccessibilityNodeInfoCompat node

the node to populate with information about the host view

onPopulateNodeForVirtualView

Added in 1.0.0
protected abstract void onPopulateNodeForVirtualView(
    int virtualViewId,
    @NonNull 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 ACTION_FOCUS, ACTION_CLEAR_FOCUS, ACTION_ACCESSIBILITY_FOCUS, or 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
int virtualViewId

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

@NonNull AccessibilityNodeInfoCompat node

The node to populate

onVirtualViewKeyboardFocusChanged

Added in 1.0.0
protected void onVirtualViewKeyboardFocusChanged(int virtualViewId, boolean hasFocus)

Called when the focus state of a virtual view changes.

Parameters
int virtualViewId

the virtual view identifier

boolean hasFocus

true if the view has focus, false otherwise