* 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 {@link 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 {@link AccessibilityNodeInfo}s * 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: *
* *
* // "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
* }
* }
* }
* }
* }
*
*
* 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;
* }
* }
* };
* }
* }
* virtualViewId
* or the host View itself if virtualViewId equals to {@link #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. *
* * @param virtualViewId A client defined virtual view id. * @return A populated {@link AccessibilityNodeInfo} for a virtual descendant or the * host View. * * @see View#createAccessibilityNodeInfo() * @see AccessibilityNodeInfo */ public @Nullable AccessibilityNodeInfo createAccessibilityNodeInfo(int virtualViewId) { return null; } /** * Adds extra data to an {@link 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. *
* * @param virtualViewId The virtual view id used to create the node * @param info The info to which to add the extra data * @param extraDataKey A key specifying the type of extra data to add to the info. The * extra data should be added to the {@link Bundle} returned by * the info's {@link AccessibilityNodeInfo#getExtras} method. * @param arguments A {@link Bundle} holding any arguments relevant for this request. * * @see AccessibilityNodeInfo#setAvailableExtraData(List) */ public void addExtraDataToAccessibilityNodeInfo( int virtualViewId, AccessibilityNodeInfo info, String extraDataKey, Bundle arguments) { } /** * Performs an accessibility action on a virtual view, such as a descendant of the * host View, with the givenvirtualViewId or the host View itself
* if virtualViewId equals to {@link #HOST_VIEW_ID}.
*
* @param virtualViewId A client defined virtual view id.
* @param action The action to perform.
* @param arguments Optional action arguments.
* @return True if the action was performed.
*
* @see View#performAccessibilityAction(int, Bundle)
* @see #createAccessibilityNodeInfo(int)
* @see AccessibilityNodeInfo
*/
public boolean performAction(int virtualViewId, int action, @Nullable Bundle arguments) {
return false;
}
/**
* Finds {@link AccessibilityNodeInfo}s 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 {@link #HOST_VIEW_ID}.
*
* @param virtualViewId A client defined virtual view id which defined
* the root of the tree in which to perform the search.
* @param text The searched text.
* @return A list of node info.
*
* @see #createAccessibilityNodeInfo(int)
* @see AccessibilityNodeInfo
*/
public @Nullable List