/*
* 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.
* <h3>Lifecycle</h3>
* <p>
* 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.
* </p>
* <h3>Declaration</h3>
* <p>
* 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:
* </p>
* <pre> <service android:name=".MyAccessibilityService">
* <intent-filter>
* <action android:name="android.accessibilityservice.AccessibilityService" />
* </intent-filter>
* . . .
* </service></pre>
* <h3>Configuration</h3>
* <p>
* 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.
* </p>
* <p>
* There are two approaches for configuring an accessibility service:
* </p>
* <ul>
* <li>
* Providing a {@link #SERVICE_META_DATA meta-data} entry in the manifest when declaring
* the service. A service declaration with a meta-data tag is presented below:
* <pre> <service android:name=".MyAccessibilityService">
* <intent-filter>
* <action android:name="android.accessibilityservice.AccessibilityService" />
* </intent-filter>
* <meta-data android:name="android.accessibilityservice" android:resource="@xml/accessibilityservice" />
* </service></pre>
* <p class="note">
* <strong>Note:</strong> This approach enables setting all properties.
* </p>
* <p>
* For more details refer to {@link #SERVICE_META_DATA} and
* <code><{@link android.R.styleable#AccessibilityService accessibility-service}></code>.
* </p>
* </li>
* <li>
* Calling {@link AccessibilityService#setServiceInfo(AccessibilityServiceInfo)}. Note
* that this method can be called any time to dynamically change the service configuration.
* <p class="note">
* <strong>Note:</strong> This approach enables setting only dynamically configurable properties:
* {@link AccessibilityServiceInfo#eventTypes},
* {@link AccessibilityServiceInfo#feedbackType},
* {@link AccessibilityServiceInfo#flags},
* {@link AccessibilityServiceInfo#notificationTimeout},
* {@link AccessibilityServiceInfo#packageNames}
* </p>
* <p>
* For more details refer to {@link AccessibilityServiceInfo}.
* </p>
* </li>
* </ul>
* <h3>Retrieving window content</h3>
* <p>
* 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}.
* </p>
* <p>
* 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.
* </p>
* <p>
* 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.
* </p>
* <p class="note">
* <strong>Note</strong> 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:
* <ul>
* <li>
* Register for all event types with no notification timeout and keep track for the active
* window by calling {@link AccessibilityEvent#getWindowId()} of the last received event and
* compare this with the {@link AccessibilityNodeInfo#getWindowId()} before calling retrieval
* methods on the latter.
* </li>
* <li>
* Prepare that a retrieval method on {@link AccessibilityNodeInfo} may fail since the
* active window has changed and the service did not get the accessibility event yet. Note
* that it is possible to have a retrieval method failing even adopting the strategy
* specified in the previous bullet because the accessibility event dispatch is asynchronous
* and crosses process boundaries.
* </li>
* </ul>
* </p>
* <h3>Notification strategy</h3>
* <p>
* 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.
* </p>
* <p class="note">
* <strong>Note:</strong> 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.</p>
* <h3>Event types</h3>
* <ul>
* <li>{@link AccessibilityEvent#TYPE_VIEW_CLICKED}
* <li>{@link AccessibilityEvent#TYPE_VIEW_LONG_CLICKED}
* <li>{@link AccessibilityEvent#TYPE_VIEW_FOCUSED}
* <li>{@link AccessibilityEvent#TYPE_VIEW_SELECTED}
* <li>{@link AccessibilityEvent#TYPE_VIEW_TEXT_CHANGED}
* <li>{@link AccessibilityEvent#TYPE_WINDOW_STATE_CHANGED}
* <li>{@link AccessibilityEvent#TYPE_NOTIFICATION_STATE_CHANGED}
* <li>{@link AccessibilityEvent#TYPE_TOUCH_EXPLORATION_GESTURE_START}
* <li>{@link AccessibilityEvent#TYPE_TOUCH_EXPLORATION_GESTURE_END}
* <li>{@link AccessibilityEvent#TYPE_VIEW_HOVER_ENTER}
* <li>{@link AccessibilityEvent#TYPE_VIEW_HOVER_EXIT}
* <li>{@link AccessibilityEvent#TYPE_VIEW_SCROLLED}
* <li>{@link AccessibilityEvent#TYPE_VIEW_TEXT_SELECTION_CHANGED}
* <li>{@link AccessibilityEvent#TYPE_WINDOW_CONTENT_CHANGED}
* </ul>
* <h3>Feedback types</h3>
* <ul>
* <li>{@link AccessibilityServiceInfo#FEEDBACK_AUDIBLE}
* <li>{@link AccessibilityServiceInfo#FEEDBACK_HAPTIC}
* <li>{@link AccessibilityServiceInfo#FEEDBACK_AUDIBLE}
* <li>{@link AccessibilityServiceInfo#FEEDBACK_VISUAL}
* <li>{@link AccessibilityServiceInfo#FEEDBACK_GENERIC}
* </ul>
* @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
* <code><{@link android.R.styleable#AccessibilityService accessibility-service}></code>
* tag. This is a a sample XML file configuring an accessibility service:
* <pre> <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"
* . . .
* /></pre>
*/
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.
* <p>
* 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);
}
}
}
}