/* * Copyright (C) 2009 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package android.accessibilityservice; import android.app.Service; import android.content.Intent; import android.os.IBinder; import android.os.Message; import android.os.RemoteException; import android.util.Log; import android.view.accessibility.AccessibilityEvent; import android.view.accessibility.AccessibilityInteractionClient; import android.view.accessibility.AccessibilityNodeInfo; import com.android.internal.os.HandlerCaller; /** * An accessibility service runs in the background and receives callbacks by the system * when {@link AccessibilityEvent}s are fired. Such events denote some state transition * in the user interface, for example, the focus has changed, a button has been clicked, * etc. Such a service can optionally request the capability for querying the content * of the active window. Development of an accessibility service requires extending this * class and implementing its abstract methods. *

Lifecycle

*

* The lifecycle of an accessibility service is managed exclusively by the system and * follows the established service life cycle. Additionally, starting or stopping an * accessibility service is triggered exclusively by an explicit user action through * enabling or disabling it in the device settings. After the system binds to a service it * calls {@link AccessibilityService#onServiceConnected()}. This method can be * overriden by clients that want to perform post binding setup. *

*

Declaration

*

* An accessibility is declared as any other service in an AndroidManifest.xml but it * must also specify that it handles the "android.accessibilityservice.AccessibilityService" * {@link android.content.Intent}. Failure to declare this intent will cause the system to * ignore the accessibility service. Following is an example declaration: *

*
 <service android:name=".MyAccessibilityService">
 *     <intent-filter>
 *         <action android:name="android.accessibilityservice.AccessibilityService" />
 *     </intent-filter>
 *     . . .
 * </service>
*

Configuration

*

* An accessibility service can be configured to receive specific types of accessibility events, * listen only to specific packages, get events from each type only once in a given time frame, * retrieve window content, specify a settings activity, etc. *

*

* There are two approaches for configuring an accessibility service: *

* *

Retrieving window content

*

* An service can specify in its declaration that it can retrieve the active window * content which is represented as a tree of {@link AccessibilityNodeInfo}. Note that * declaring this capability requires that the service declares its configuration via * an XML resource referenced by {@link #SERVICE_META_DATA}. *

*

* For security purposes an accessibility service can retrieve only the content of the * currently active window. The currently active window is defined as the window from * which was fired the last event of the following types: * {@link AccessibilityEvent#TYPE_WINDOW_STATE_CHANGED}, * {@link AccessibilityEvent#TYPE_VIEW_HOVER_ENTER}, * {@link AccessibilityEvent#TYPE_VIEW_HOVER_EXIT}, * In other words, the last window that was shown or the last window that the user has touched * during touch exploration. *

*

* The entry point for retrieving window content is through calling * {@link AccessibilityEvent#getSource() AccessibilityEvent.getSource()} of the last received * event of the above types or a previous event from the same window * (see {@link AccessibilityEvent#getWindowId() AccessibilityEvent.getWindowId()}). Invoking * this method will return an {@link AccessibilityNodeInfo} that can be used to traverse the * window content which represented as a tree of such objects. *

*

* Note An accessibility service may have requested to be notified for * a subset of the event types, thus be unaware that the active window has changed. Therefore * accessibility service that would like to retrieve window content should: *

*

*

Notification strategy

*

* For each feedback type only one accessibility service is notified. Services are notified * in the order of registration. Hence, if two services are registered for the same * feedback type in the same package the first one wins. It is possible however, to * register a service as the default one for a given feedback type. In such a case this * service is invoked if no other service was interested in the event. In other words, default * services do not compete with other services and are notified last regardless of the * registration order. This enables "generic" accessibility services that work reasonably * well with most applications to coexist with "polished" ones that are targeted for * specific applications. *

*

* Note: The event notification timeout is useful to avoid propagating * events to the client too frequently since this is accomplished via an expensive * interprocess call. One can think of the timeout as a criteria to determine when * event generation has settled down.

*

Event types

* *

Feedback types

* * @see AccessibilityEvent * @see AccessibilityServiceInfo * @see android.view.accessibility.AccessibilityManager */ public abstract class AccessibilityService extends Service { /** * The {@link Intent} that must be declared as handled by the service. */ public static final String SERVICE_INTERFACE = "android.accessibilityservice.AccessibilityService"; /** * Name under which an AccessibilityService component publishes information * about itself. This meta-data must reference an XML resource containing an * <{@link android.R.styleable#AccessibilityService accessibility-service}> * tag. This is a a sample XML file configuring an accessibility service: *
 <accessibility-service
     *     android:accessibilityEventTypes="typeViewClicked|typeViewFocused"
     *     android:packageNames="foo.bar, foo.baz"
     *     android:accessibilityFeedbackType="feedbackSpoken"
     *     android:notificationTimeout="100"
     *     android:accessibilityFlags="flagDefault"
     *     android:settingsActivity="foo.bar.TestBackActivity"
     *     android:canRetrieveWindowContent="true"
     *     . . .
     * />
*/ public static final String SERVICE_META_DATA = "android.accessibilityservice"; private static final String LOG_TAG = "AccessibilityService"; private AccessibilityServiceInfo mInfo; private int mConnectionId; /** * Callback for {@link android.view.accessibility.AccessibilityEvent}s. * * @param event An event. */ public abstract void onAccessibilityEvent(AccessibilityEvent event); /** * Callback for interrupting the accessibility feedback. */ public abstract void onInterrupt(); /** * This method is a part of the {@link AccessibilityService} lifecycle and is * called after the system has successfully bound to the service. If is * convenient to use this method for setting the {@link AccessibilityServiceInfo}. * * @see AccessibilityServiceInfo * @see #setServiceInfo(AccessibilityServiceInfo) */ protected void onServiceConnected() { } /** * Sets the {@link AccessibilityServiceInfo} that describes this service. *

* Note: You can call this method any time but the info will be picked up after * the system has bound to this service and when this method is called thereafter. * * @param info The info. */ public final void setServiceInfo(AccessibilityServiceInfo info) { mInfo = info; sendServiceInfo(); } /** * Sets the {@link AccessibilityServiceInfo} for this service if the latter is * properly set and there is an {@link IAccessibilityServiceConnection} to the * AccessibilityManagerService. */ private void sendServiceInfo() { IAccessibilityServiceConnection connection = AccessibilityInteractionClient.getInstance().getConnection(mConnectionId); if (mInfo != null && connection != null) { try { connection.setServiceInfo(mInfo); } catch (RemoteException re) { Log.w(LOG_TAG, "Error while setting AccessibilityServiceInfo", re); } } } /** * Implement to return the implementation of the internal accessibility * service interface. */ @Override public final IBinder onBind(Intent intent) { return new IEventListenerWrapper(this); } /** * Implements the internal {@link IEventListener} interface to convert * incoming calls to it back to calls on an {@link AccessibilityService}. */ class IEventListenerWrapper extends IEventListener.Stub implements HandlerCaller.Callback { private static final int DO_SET_SET_CONNECTION = 10; private static final int DO_ON_INTERRUPT = 20; private static final int DO_ON_ACCESSIBILITY_EVENT = 30; private final HandlerCaller mCaller; private final AccessibilityService mTarget; public IEventListenerWrapper(AccessibilityService context) { mTarget = context; mCaller = new HandlerCaller(context, this); } public void setConnection(IAccessibilityServiceConnection connection, int connectionId) { Message message = mCaller.obtainMessageIO(DO_SET_SET_CONNECTION, connectionId, connection); mCaller.sendMessage(message); } public void onInterrupt() { Message message = mCaller.obtainMessage(DO_ON_INTERRUPT); mCaller.sendMessage(message); } public void onAccessibilityEvent(AccessibilityEvent event) { Message message = mCaller.obtainMessageO(DO_ON_ACCESSIBILITY_EVENT, event); mCaller.sendMessage(message); } public void executeMessage(Message message) { switch (message.what) { case DO_ON_ACCESSIBILITY_EVENT : AccessibilityEvent event = (AccessibilityEvent) message.obj; if (event != null) { mTarget.onAccessibilityEvent(event); event.recycle(); } return; case DO_ON_INTERRUPT : mTarget.onInterrupt(); return; case DO_SET_SET_CONNECTION : final int connectionId = message.arg1; IAccessibilityServiceConnection connection = (IAccessibilityServiceConnection) message.obj; if (connection != null) { AccessibilityInteractionClient.getInstance().addConnection(connectionId, connection); mConnectionId = connectionId; mTarget.onServiceConnected(); } else { AccessibilityInteractionClient.getInstance().removeConnection(connectionId); mConnectionId = AccessibilityInteractionClient.NO_ID; // TODO: Do we need a onServiceDisconnected callback? } return; default : Log.w(LOG_TAG, "Unknown message type " + message.what); } } } }