AccessibilityNodeProvider

abstract class 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) {
                      <var>host-view-id</var>-> {
                          val node = AccessibilityNodeInfo.obtain(view)
                          node.addChild(view, <var>child-view-id</var>)
                          // Set other attributes like screenReaderFocusable
                          // and contentDescription.
                          return node
                      }
                      <var>child-view-id</var>-> {
                          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(<var>coords-of-edges-relative-to-screen</var>))
                          return node
                      }
                      else -> return null
                  }
              }
 
              override fun performAction(
                  virtualViewId: Int,
                  action: Int,
                  arguments: Bundle
              ): Boolean {
                  if (virtualViewId == <var>host-view-id</var>) {
                      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 == <var>host-view-id</var>) {
                      AccessibilityNodeInfo node = AccessibilityNodeInfo.obtain(view);
                      node.addChild(view, <var>child-view-id</var>);
                      // Set other attributes like screenReaderFocusable and contentDescription.
                      return node;
                  } else if (virtualViewId == <var>child-view-id</var>) {
                      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(<var>coordinates-of-edges-relative-to-screen</var>));
                      return node;
                  } else {
                      return null;
                  }
              }
 
              @Override
              public boolean performAction(int virtualViewId, int action, Bundle arguments) {
                  if (virtualViewId == <var>host-view-id</var>) {
                      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

static val HOST_VIEW_ID: Int

Value: -1

Public constructors

AccessibilityNodeProvider()

Public methods

open fun addExtraDataToAccessibilityNodeInfo(
    virtualViewId: Int, 
    info: AccessibilityNodeInfo!, 
    extraDataKey: String!, 
    arguments: Bundle!
): Unit

open fun createAccessibilityNodeInfo(virtualViewId: Int): AccessibilityNodeInfo?

open fun findAccessibilityNodeInfosByText(
    text: String!, 
    virtualViewId: Int
): MutableList<AccessibilityNodeInfo!>?

open fun findFocus(focus: Int): AccessibilityNodeInfo?

open fun performAction(
    virtualViewId: Int, 
    action: Int, 
    arguments: Bundle?
): Boolean