AccessibilityNodeProvider

public abstract class AccessibilityNodeProvider
extends Object

java.lang.Object
   ↳ android.view.accessibility.AccessibilityNodeProvider


This class is the contract a client should implement to enable support of a virtual view hierarchy rooted at a given view for accessibility purposes. A virtual view hierarchy is a tree of imaginary Views that is reported as a part of the view hierarchy when an AccessibilityService explores the window content. Since the virtual View tree does not exist this class is responsible for managing the AccessibilityNodeInfos describing that tree to accessibility services.

The main use case of these APIs is to enable a custom view that draws complex content, for example a monthly calendar grid, to be presented as a tree of logical nodes, for example month days each containing events, thus conveying its logical structure.

A typical use case is to override View#getAccessibilityNodeProvider() of the View that is a root of a virtual View hierarchy to return an instance of this class. In such a case this instance is responsible for managing AccessibilityNodeInfos describing the virtual sub-tree rooted at the View including the one representing the View itself. Similarly the returned instance is responsible for performing accessibility actions on any virtual view or the root view itself. For example:

Kotlin

 // "view" is the View instance on which this class performs accessibility functions.
 class MyCalendarViewAccessibilityDelegate(
       private var view: MyCalendarView) : AccessibilityDelegate() {
     override fun getAccessibilityNodeProvider(host: View): AccessibilityNodeProvider {
         return object : AccessibilityNodeProvider() {
             override fun createAccessibilityNodeInfo(virtualViewId: Int):
                     AccessibilityNodeInfo? {
                 when (virtualViewId) {
                     host-view-id -> {
                         val node = AccessibilityNodeInfo.obtain(view)
                         node.addChild(view, child-view-id)
                         // Set other attributes like screenReaderFocusable
                         // and contentDescription.
                         return node
                     }
                     child-view-id -> {
                         val node = AccessibilityNodeInfo
                                 .obtain(view, virtualViewId)
                         node.setParent(view)
                         node.addAction(ACTION_SCROLL_UP)
                         node.addAction(ACTION_SCROLL_DOWN)
                         // Set other attributes like focusable and visibleToUser.
                         node.setBoundsInScreen(
                                 Rect(coords-of-edges-relative-to-screen))
                         return node
                     }
                     else -> return null
                 }
             }

             override fun performAction(
                 virtualViewId: Int,
                 action: Int,
                 arguments: Bundle
             ): Boolean {
                 if (virtualViewId == host-view-id) {
                     return view.performAccessibilityAction(action, arguments)
                 }
                 when (action) {
                     ACTION_SCROLL_UP.id -> {
                         // Implement logic in a separate method.
                         navigateToPreviousMonth()

                         return true
                     }
                     ACTION_SCROLL_DOWN.id ->
                         // Implement logic in a separate method.
                         navigateToNextMonth()

                         return true
                     else -> return false
                 }
             }
         }
     }
 }
 

Java

 final class MyCalendarViewAccessibilityDelegate extends AccessibilityDelegate {
     // The View instance on which this class performs accessibility functions.
     private final MyCalendarView view;

     MyCalendarViewAccessibilityDelegate(MyCalendarView view) {
         this.view = view;
     }

     @Override
     public AccessibilityNodeProvider getAccessibilityNodeProvider(View host) {
         return new AccessibilityNodeProvider() {
             @Override
             @Nullable
             public AccessibilityNodeInfo createAccessibilityNodeInfo(int virtualViewId) {
                 if (virtualViewId == host-view-id) {
                     AccessibilityNodeInfo node = AccessibilityNodeInfo.obtain(view);
                     node.addChild(view, child-view-id);
                     // Set other attributes like screenReaderFocusable and contentDescription.
                     return node;
                 } else if (virtualViewId == child-view-id) {
                     AccessibilityNodeInfo node =
                         AccessibilityNodeInfo.obtain(view, virtualViewId);
                     node.setParent(view);
                     node.addAction(ACTION_SCROLL_UP);
                     node.addAction(ACTION_SCROLL_DOWN);
                     // Set other attributes like focusable and visibleToUser.
                     node.setBoundsInScreen(
                         new Rect(coordinates-of-edges-relative-to-screen));
                     return node;
                 } else {
                     return null;
                 }
             }

             @Override
             public boolean performAction(int virtualViewId, int action, Bundle arguments) {
                 if (virtualViewId == host-view-id) {
                     return view.performAccessibilityAction(action, arguments);
                 }

                 if (action == ACTION_SCROLL_UP.getId()) {
                     // Implement logic in a separate method.
                     navigateToPreviousMonth();

                     return true;
                 } else if (action == ACTION_SCROLL_DOWN.getId()) {
                     // Implement logic in a separate method.
                     navigateToNextMonth();

                     return true;
                 } else {
                     return false;
                 }
             }
         };
     }
 }
 

Summary

Constants

int HOST_VIEW_ID

The virtual id for the hosting View.

Public constructors

AccessibilityNodeProvider()

Public methods

void addExtraDataToAccessibilityNodeInfo(int virtualViewId, AccessibilityNodeInfo info, String extraDataKey, Bundle arguments)

Adds extra data to an AccessibilityNodeInfo based on an explicit request for the additional data.

AccessibilityNodeInfo createAccessibilityNodeInfo(int virtualViewId)

Returns an AccessibilityNodeInfo representing a virtual view, such as a descendant of the host View, with the given virtualViewId or the host View itself if virtualViewId equals to HOST_VIEW_ID.

List<AccessibilityNodeInfo> findAccessibilityNodeInfosByText(String text, int virtualViewId)

Finds AccessibilityNodeInfos by text.

AccessibilityNodeInfo findFocus(int focus)

Find the virtual view, such as a descendant of the host View, that has the specified focus type.

boolean performAction(int virtualViewId, int action, Bundle arguments)

Performs an accessibility action on a virtual view, such as a descendant of the host View, with the given virtualViewId or the host View itself if virtualViewId equals to HOST_VIEW_ID.

Inherited methods

Constants

HOST_VIEW_ID

Added in API level 21
public static final int HOST_VIEW_ID

The virtual id for the hosting View.

Constant Value: -1 (0xffffffff)

Public constructors

AccessibilityNodeProvider

public AccessibilityNodeProvider ()

Public methods

addExtraDataToAccessibilityNodeInfo

Added in API level 26
public void addExtraDataToAccessibilityNodeInfo (int virtualViewId, 
                AccessibilityNodeInfo info, 
                String extraDataKey, 
                Bundle arguments)

Adds extra data to an AccessibilityNodeInfo based on an explicit request for the additional data.

This method only needs to be implemented if a virtual view offers to provide additional data.

Parameters
virtualViewId int: The virtual view id used to create the node

info AccessibilityNodeInfo: The info to which to add the extra data

extraDataKey String: A key specifying the type of extra data to add to the info. The extra data should be added to the Bundle returned by the info's AccessibilityNodeInfo#getExtras method.

arguments Bundle: A Bundle holding any arguments relevant for this request.

createAccessibilityNodeInfo

Added in API level 16
public AccessibilityNodeInfo createAccessibilityNodeInfo (int virtualViewId)

Returns an AccessibilityNodeInfo representing a virtual view, such as a descendant of the host View, with the given virtualViewId or the host View itself if virtualViewId equals to HOST_VIEW_ID.

A virtual descendant is an imaginary View that is reported as a part of the view hierarchy for accessibility purposes. This enables custom views that draw complex content to report them selves as a tree of virtual views, thus conveying their logical structure.

The implementer is responsible for obtaining an accessibility node info from the pool of reusable instances and setting the desired properties of the node info before returning it.

Parameters
virtualViewId int: A client defined virtual view id.

Returns
AccessibilityNodeInfo A populated AccessibilityNodeInfo for a virtual descendant or the host View. This value may be null.

findAccessibilityNodeInfosByText

Added in API level 16
public List<AccessibilityNodeInfo> findAccessibilityNodeInfosByText (String text, 
                int virtualViewId)

Finds AccessibilityNodeInfos by text. The match is case insensitive containment. The search is relative to the virtual view, i.e. a descendant of the host View, with the given virtualViewId or the host View itself virtualViewId equals to HOST_VIEW_ID.

Parameters
text String: The searched text.

virtualViewId int: A client defined virtual view id which defined the root of the tree in which to perform the search.

Returns
List<AccessibilityNodeInfo> A list of node info. This value may be null.

findFocus

Added in API level 19
public AccessibilityNodeInfo findFocus (int focus)

Find the virtual view, such as a descendant of the host View, that has the specified focus type.

Parameters
focus int: The focus to find. One of AccessibilityNodeInfo#FOCUS_INPUT or AccessibilityNodeInfo#FOCUS_ACCESSIBILITY.

Returns
AccessibilityNodeInfo The node info of the focused view or null.

performAction

Added in API level 16
public boolean performAction (int virtualViewId, 
                int action, 
                Bundle arguments)

Performs an accessibility action on a virtual view, such as a descendant of the host View, with the given virtualViewId or the host View itself if virtualViewId equals to HOST_VIEW_ID.

Parameters
virtualViewId int: A client defined virtual view id.

action int: The action to perform.

arguments Bundle: Optional action arguments. This value may be null.

Returns
boolean True if the action was performed.