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      1 /*
      2  * Copyright (C) 2011 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package android.view.accessibility;
     18 
     19 import android.accessibilityservice.AccessibilityService;
     20 import android.os.Bundle;
     21 import android.view.View;
     22 
     23 import java.util.List;
     24 
     25 /**
     26  * This class is the contract a client should implement to enable support of a
     27  * virtual view hierarchy rooted at a given view for accessibility purposes. A virtual
     28  * view hierarchy is a tree of imaginary Views that is reported as a part of the view
     29  * hierarchy when an {@link AccessibilityService} explores the window content.
     30  * Since the virtual View tree does not exist this class is responsible for
     31  * managing the {@link AccessibilityNodeInfo}s describing that tree to accessibility
     32  * services.
     33  * </p>
     34  * <p>
     35  * The main use case of these APIs is to enable a custom view that draws complex content,
     36  * for example a monthly calendar grid, to be presented as a tree of logical nodes,
     37  * for example month days each containing events, thus conveying its logical structure.
     38  * <p>
     39  * <p>
     40  * A typical use case is to override {@link View#getAccessibilityNodeProvider()} of the
     41  * View that is a root of a virtual View hierarchy to return an instance of this class.
     42  * In such a case this instance is responsible for managing {@link AccessibilityNodeInfo}s
     43  * describing the virtual sub-tree rooted at the View including the one representing the
     44  * View itself. Similarly the returned instance is responsible for performing accessibility
     45  * actions on any virtual view or the root view itself. For example:
     46  * </p>
     47  * <pre>
     48  *     getAccessibilityNodeProvider(
     49  *         if (mAccessibilityNodeProvider == null) {
     50  *             mAccessibilityNodeProvider = new AccessibilityNodeProvider() {
     51  *                 public boolean performAction(int action, int virtualDescendantId) {
     52  *                     // Implementation.
     53  *                     return false;
     54  *                 }
     55  *
     56  *                 public List<AccessibilityNodeInfo> findAccessibilityNodeInfosByText(String text,
     57  *                         int virtualDescendantId) {
     58  *                     // Implementation.
     59  *                     return null;
     60  *                 }
     61  *
     62  *                 public AccessibilityNodeInfo createAccessibilityNodeInfo(int virtualDescendantId) {
     63  *                     // Implementation.
     64  *                     return null;
     65  *                 }
     66  *             });
     67  *     return mAccessibilityNodeProvider;
     68  * </pre>
     69  */
     70 public abstract class AccessibilityNodeProvider {
     71 
     72     /**
     73      * The virtual id for the hosting View.
     74      */
     75     public static final int HOST_VIEW_ID = -1;
     76 
     77     /**
     78      * Returns an {@link AccessibilityNodeInfo} representing a virtual view,
     79      * i.e. a descendant of the host View, with the given <code>virtualViewId</code>
     80      * or the host View itself if <code>virtualViewId</code> equals to {@link #HOST_VIEW_ID}.
     81      * <p>
     82      * A virtual descendant is an imaginary View that is reported as a part of the view
     83      * hierarchy for accessibility purposes. This enables custom views that draw complex
     84      * content to report them selves as a tree of virtual views, thus conveying their
     85      * logical structure.
     86      * </p>
     87      * <p>
     88      * The implementer is responsible for obtaining an accessibility node info from the
     89      * pool of reusable instances and setting the desired properties of the node info
     90      * before returning it.
     91      * </p>
     92      *
     93      * @param virtualViewId A client defined virtual view id.
     94      * @return A populated {@link AccessibilityNodeInfo} for a virtual descendant or the
     95      *     host View.
     96      *
     97      * @see View#createAccessibilityNodeInfo()
     98      * @see AccessibilityNodeInfo
     99      */
    100     public AccessibilityNodeInfo createAccessibilityNodeInfo(int virtualViewId) {
    101         return null;
    102     }
    103 
    104     /**
    105      * Performs an accessibility action on a virtual view, i.e. a descendant of the
    106      * host View, with the given <code>virtualViewId</code> or the host View itself
    107      * if <code>virtualViewId</code> equals to {@link #HOST_VIEW_ID}.
    108      *
    109      * @param virtualViewId A client defined virtual view id.
    110      * @param action The action to perform.
    111      * @param arguments Optional action arguments.
    112      * @return True if the action was performed.
    113      *
    114      * @see View#performAccessibilityAction(int, Bundle)
    115      * @see #createAccessibilityNodeInfo(int)
    116      * @see AccessibilityNodeInfo
    117      */
    118     public boolean performAction(int virtualViewId, int action, Bundle arguments) {
    119         return false;
    120     }
    121 
    122     /**
    123      * Finds {@link AccessibilityNodeInfo}s by text. The match is case insensitive
    124      * containment. The search is relative to the virtual view, i.e. a descendant of the
    125      * host View, with the given <code>virtualViewId</code> or the host View itself
    126      * <code>virtualViewId</code> equals to {@link #HOST_VIEW_ID}.
    127      *
    128      * @param virtualViewId A client defined virtual view id which defined
    129      *     the root of the tree in which to perform the search.
    130      * @param text The searched text.
    131      * @return A list of node info.
    132      *
    133      * @see #createAccessibilityNodeInfo(int)
    134      * @see AccessibilityNodeInfo
    135      */
    136     public List<AccessibilityNodeInfo> findAccessibilityNodeInfosByText(String text,
    137             int virtualViewId) {
    138         return null;
    139     }
    140 
    141     /**
    142      * Find the virtual view, i.e. a descendant of the host View, that has the
    143      * specified focus type.
    144      *
    145      * @param focus The focus to find. One of
    146      *            {@link AccessibilityNodeInfo#FOCUS_INPUT} or
    147      *            {@link AccessibilityNodeInfo#FOCUS_ACCESSIBILITY}.
    148      * @return The node info of the focused view or null.
    149      * @see AccessibilityNodeInfo#FOCUS_INPUT
    150      * @see AccessibilityNodeInfo#FOCUS_ACCESSIBILITY
    151      */
    152     public AccessibilityNodeInfo findFocus(int focus) {
    153         return null;
    154     }
    155 }
    156