1/* 2 * Copyright (C) 2009 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 17package android.accessibilityservice; 18 19import android.app.Service; 20import android.content.Intent; 21import android.os.IBinder; 22import android.os.Message; 23import android.os.RemoteException; 24import android.util.Log; 25import android.view.accessibility.AccessibilityEvent; 26import android.view.accessibility.AccessibilityInteractionClient; 27import android.view.accessibility.AccessibilityNodeInfo; 28 29import com.android.internal.os.HandlerCaller; 30 31/** 32 * An accessibility service runs in the background and receives callbacks by the system 33 * when {@link AccessibilityEvent}s are fired. Such events denote some state transition 34 * in the user interface, for example, the focus has changed, a button has been clicked, 35 * etc. Such a service can optionally request the capability for querying the content 36 * of the active window. Development of an accessibility service requires extending this 37 * class and implementing its abstract methods. 38 * <h3>Lifecycle</h3> 39 * <p> 40 * The lifecycle of an accessibility service is managed exclusively by the system and 41 * follows the established service life cycle. Additionally, starting or stopping an 42 * accessibility service is triggered exclusively by an explicit user action through 43 * enabling or disabling it in the device settings. After the system binds to a service it 44 * calls {@link AccessibilityService#onServiceConnected()}. This method can be 45 * overriden by clients that want to perform post binding setup. 46 * </p> 47 * <h3>Declaration</h3> 48 * <p> 49 * An accessibility is declared as any other service in an AndroidManifest.xml but it 50 * must also specify that it handles the "android.accessibilityservice.AccessibilityService" 51 * {@link android.content.Intent}. Failure to declare this intent will cause the system to 52 * ignore the accessibility service. Following is an example declaration: 53 * </p> 54 * <pre> <service android:name=".MyAccessibilityService"> 55 * <intent-filter> 56 * <action android:name="android.accessibilityservice.AccessibilityService" /> 57 * </intent-filter> 58 * . . . 59 * </service></pre> 60 * <h3>Configuration</h3> 61 * <p> 62 * An accessibility service can be configured to receive specific types of accessibility events, 63 * listen only to specific packages, get events from each type only once in a given time frame, 64 * retrieve window content, specify a settings activity, etc. 65 * </p> 66 * <p> 67 * There are two approaches for configuring an accessibility service: 68 * </p> 69 * <ul> 70 * <li> 71 * Providing a {@link #SERVICE_META_DATA meta-data} entry in the manifest when declaring 72 * the service. A service declaration with a meta-data tag is presented below: 73 * <pre> <service android:name=".MyAccessibilityService"> 74 * <intent-filter> 75 * <action android:name="android.accessibilityservice.AccessibilityService" /> 76 * </intent-filter> 77 * <meta-data android:name="android.accessibilityservice" android:resource="@xml/accessibilityservice" /> 78 * </service></pre> 79 * <p class="note"> 80 * <strong>Note:</strong> This approach enables setting all properties. 81 * </p> 82 * <p> 83 * For more details refer to {@link #SERVICE_META_DATA} and 84 * <code><{@link android.R.styleable#AccessibilityService accessibility-service}></code>. 85 * </p> 86 * </li> 87 * <li> 88 * Calling {@link AccessibilityService#setServiceInfo(AccessibilityServiceInfo)}. Note 89 * that this method can be called any time to dynamically change the service configuration. 90 * <p class="note"> 91 * <strong>Note:</strong> This approach enables setting only dynamically configurable properties: 92 * {@link AccessibilityServiceInfo#eventTypes}, 93 * {@link AccessibilityServiceInfo#feedbackType}, 94 * {@link AccessibilityServiceInfo#flags}, 95 * {@link AccessibilityServiceInfo#notificationTimeout}, 96 * {@link AccessibilityServiceInfo#packageNames} 97 * </p> 98 * <p> 99 * For more details refer to {@link AccessibilityServiceInfo}. 100 * </p> 101 * </li> 102 * </ul> 103 * <h3>Retrieving window content</h3> 104 * <p> 105 * An service can specify in its declaration that it can retrieve the active window 106 * content which is represented as a tree of {@link AccessibilityNodeInfo}. Note that 107 * declaring this capability requires that the service declares its configuration via 108 * an XML resource referenced by {@link #SERVICE_META_DATA}. 109 * </p> 110 * <p> 111 * For security purposes an accessibility service can retrieve only the content of the 112 * currently active window. The currently active window is defined as the window from 113 * which was fired the last event of the following types: 114 * {@link AccessibilityEvent#TYPE_WINDOW_STATE_CHANGED}, 115 * {@link AccessibilityEvent#TYPE_VIEW_HOVER_ENTER}, 116 * {@link AccessibilityEvent#TYPE_VIEW_HOVER_EXIT}, 117 * In other words, the last window that was shown or the last window that the user has touched 118 * during touch exploration. 119 * </p> 120 * <p> 121 * The entry point for retrieving window content is through calling 122 * {@link AccessibilityEvent#getSource() AccessibilityEvent.getSource()} of the last received 123 * event of the above types or a previous event from the same window 124 * (see {@link AccessibilityEvent#getWindowId() AccessibilityEvent.getWindowId()}). Invoking 125 * this method will return an {@link AccessibilityNodeInfo} that can be used to traverse the 126 * window content which represented as a tree of such objects. 127 * </p> 128 * <p class="note"> 129 * <strong>Note</strong> An accessibility service may have requested to be notified for 130 * a subset of the event types, thus be unaware that the active window has changed. Therefore 131 * accessibility service that would like to retrieve window content should: 132 * <ul> 133 * <li> 134 * Register for all event types with no notification timeout and keep track for the active 135 * window by calling {@link AccessibilityEvent#getWindowId()} of the last received event and 136 * compare this with the {@link AccessibilityNodeInfo#getWindowId()} before calling retrieval 137 * methods on the latter. 138 * </li> 139 * <li> 140 * Prepare that a retrieval method on {@link AccessibilityNodeInfo} may fail since the 141 * active window has changed and the service did not get the accessibility event yet. Note 142 * that it is possible to have a retrieval method failing even adopting the strategy 143 * specified in the previous bullet because the accessibility event dispatch is asynchronous 144 * and crosses process boundaries. 145 * </li> 146 * </ul> 147 * </p> 148 * <h3>Notification strategy</h3> 149 * <p> 150 * For each feedback type only one accessibility service is notified. Services are notified 151 * in the order of registration. Hence, if two services are registered for the same 152 * feedback type in the same package the first one wins. It is possible however, to 153 * register a service as the default one for a given feedback type. In such a case this 154 * service is invoked if no other service was interested in the event. In other words, default 155 * services do not compete with other services and are notified last regardless of the 156 * registration order. This enables "generic" accessibility services that work reasonably 157 * well with most applications to coexist with "polished" ones that are targeted for 158 * specific applications. 159 * </p> 160 * <p class="note"> 161 * <strong>Note:</strong> The event notification timeout is useful to avoid propagating 162 * events to the client too frequently since this is accomplished via an expensive 163 * interprocess call. One can think of the timeout as a criteria to determine when 164 * event generation has settled down.</p> 165 * <h3>Event types</h3> 166 * <ul> 167 * <li>{@link AccessibilityEvent#TYPE_VIEW_CLICKED} 168 * <li>{@link AccessibilityEvent#TYPE_VIEW_LONG_CLICKED} 169 * <li>{@link AccessibilityEvent#TYPE_VIEW_FOCUSED} 170 * <li>{@link AccessibilityEvent#TYPE_VIEW_SELECTED} 171 * <li>{@link AccessibilityEvent#TYPE_VIEW_TEXT_CHANGED} 172 * <li>{@link AccessibilityEvent#TYPE_WINDOW_STATE_CHANGED} 173 * <li>{@link AccessibilityEvent#TYPE_NOTIFICATION_STATE_CHANGED} 174 * <li>{@link AccessibilityEvent#TYPE_TOUCH_EXPLORATION_GESTURE_START} 175 * <li>{@link AccessibilityEvent#TYPE_TOUCH_EXPLORATION_GESTURE_END} 176 * <li>{@link AccessibilityEvent#TYPE_VIEW_HOVER_ENTER} 177 * <li>{@link AccessibilityEvent#TYPE_VIEW_HOVER_EXIT} 178 * <li>{@link AccessibilityEvent#TYPE_VIEW_SCROLLED} 179 * <li>{@link AccessibilityEvent#TYPE_VIEW_TEXT_SELECTION_CHANGED} 180 * <li>{@link AccessibilityEvent#TYPE_WINDOW_CONTENT_CHANGED} 181 * </ul> 182 * <h3>Feedback types</h3> 183 * <ul> 184 * <li>{@link AccessibilityServiceInfo#FEEDBACK_AUDIBLE} 185 * <li>{@link AccessibilityServiceInfo#FEEDBACK_HAPTIC} 186 * <li>{@link AccessibilityServiceInfo#FEEDBACK_AUDIBLE} 187 * <li>{@link AccessibilityServiceInfo#FEEDBACK_VISUAL} 188 * <li>{@link AccessibilityServiceInfo#FEEDBACK_GENERIC} 189 * </ul> 190 * @see AccessibilityEvent 191 * @see AccessibilityServiceInfo 192 * @see android.view.accessibility.AccessibilityManager 193 */ 194public abstract class AccessibilityService extends Service { 195 /** 196 * The {@link Intent} that must be declared as handled by the service. 197 */ 198 public static final String SERVICE_INTERFACE = 199 "android.accessibilityservice.AccessibilityService"; 200 201 /** 202 * Name under which an AccessibilityService component publishes information 203 * about itself. This meta-data must reference an XML resource containing an 204 * <code><{@link android.R.styleable#AccessibilityService accessibility-service}></code> 205 * tag. This is a a sample XML file configuring an accessibility service: 206 * <pre> <accessibility-service 207 * android:accessibilityEventTypes="typeViewClicked|typeViewFocused" 208 * android:packageNames="foo.bar, foo.baz" 209 * android:accessibilityFeedbackType="feedbackSpoken" 210 * android:notificationTimeout="100" 211 * android:accessibilityFlags="flagDefault" 212 * android:settingsActivity="foo.bar.TestBackActivity" 213 * android:canRetrieveWindowContent="true" 214 * . . . 215 * /></pre> 216 */ 217 public static final String SERVICE_META_DATA = "android.accessibilityservice"; 218 219 private static final String LOG_TAG = "AccessibilityService"; 220 221 private AccessibilityServiceInfo mInfo; 222 223 private int mConnectionId; 224 225 /** 226 * Callback for {@link android.view.accessibility.AccessibilityEvent}s. 227 * 228 * @param event An event. 229 */ 230 public abstract void onAccessibilityEvent(AccessibilityEvent event); 231 232 /** 233 * Callback for interrupting the accessibility feedback. 234 */ 235 public abstract void onInterrupt(); 236 237 /** 238 * This method is a part of the {@link AccessibilityService} lifecycle and is 239 * called after the system has successfully bound to the service. If is 240 * convenient to use this method for setting the {@link AccessibilityServiceInfo}. 241 * 242 * @see AccessibilityServiceInfo 243 * @see #setServiceInfo(AccessibilityServiceInfo) 244 */ 245 protected void onServiceConnected() { 246 247 } 248 249 /** 250 * Sets the {@link AccessibilityServiceInfo} that describes this service. 251 * <p> 252 * Note: You can call this method any time but the info will be picked up after 253 * the system has bound to this service and when this method is called thereafter. 254 * 255 * @param info The info. 256 */ 257 public final void setServiceInfo(AccessibilityServiceInfo info) { 258 mInfo = info; 259 sendServiceInfo(); 260 } 261 262 /** 263 * Sets the {@link AccessibilityServiceInfo} for this service if the latter is 264 * properly set and there is an {@link IAccessibilityServiceConnection} to the 265 * AccessibilityManagerService. 266 */ 267 private void sendServiceInfo() { 268 IAccessibilityServiceConnection connection = 269 AccessibilityInteractionClient.getInstance().getConnection(mConnectionId); 270 if (mInfo != null && connection != null) { 271 try { 272 connection.setServiceInfo(mInfo); 273 } catch (RemoteException re) { 274 Log.w(LOG_TAG, "Error while setting AccessibilityServiceInfo", re); 275 } 276 } 277 } 278 279 /** 280 * Implement to return the implementation of the internal accessibility 281 * service interface. 282 */ 283 @Override 284 public final IBinder onBind(Intent intent) { 285 return new IEventListenerWrapper(this); 286 } 287 288 /** 289 * Implements the internal {@link IEventListener} interface to convert 290 * incoming calls to it back to calls on an {@link AccessibilityService}. 291 */ 292 class IEventListenerWrapper extends IEventListener.Stub 293 implements HandlerCaller.Callback { 294 295 private static final int DO_SET_SET_CONNECTION = 10; 296 private static final int DO_ON_INTERRUPT = 20; 297 private static final int DO_ON_ACCESSIBILITY_EVENT = 30; 298 299 private final HandlerCaller mCaller; 300 301 private final AccessibilityService mTarget; 302 303 public IEventListenerWrapper(AccessibilityService context) { 304 mTarget = context; 305 mCaller = new HandlerCaller(context, this); 306 } 307 308 public void setConnection(IAccessibilityServiceConnection connection, int connectionId) { 309 Message message = mCaller.obtainMessageIO(DO_SET_SET_CONNECTION, connectionId, 310 connection); 311 mCaller.sendMessage(message); 312 } 313 314 public void onInterrupt() { 315 Message message = mCaller.obtainMessage(DO_ON_INTERRUPT); 316 mCaller.sendMessage(message); 317 } 318 319 public void onAccessibilityEvent(AccessibilityEvent event) { 320 Message message = mCaller.obtainMessageO(DO_ON_ACCESSIBILITY_EVENT, event); 321 mCaller.sendMessage(message); 322 } 323 324 public void executeMessage(Message message) { 325 switch (message.what) { 326 case DO_ON_ACCESSIBILITY_EVENT : 327 AccessibilityEvent event = (AccessibilityEvent) message.obj; 328 if (event != null) { 329 mTarget.onAccessibilityEvent(event); 330 event.recycle(); 331 } 332 return; 333 case DO_ON_INTERRUPT : 334 mTarget.onInterrupt(); 335 return; 336 case DO_SET_SET_CONNECTION : 337 final int connectionId = message.arg1; 338 IAccessibilityServiceConnection connection = 339 (IAccessibilityServiceConnection) message.obj; 340 if (connection != null) { 341 AccessibilityInteractionClient.getInstance().addConnection(connectionId, 342 connection); 343 mConnectionId = connectionId; 344 mTarget.onServiceConnected(); 345 } else { 346 AccessibilityInteractionClient.getInstance().removeConnection(connectionId); 347 mConnectionId = AccessibilityInteractionClient.NO_ID; 348 // TODO: Do we need a onServiceDisconnected callback? 349 } 350 return; 351 default : 352 Log.w(LOG_TAG, "Unknown message type " + message.what); 353 } 354 } 355 } 356} 357