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Android APIs
public abstract class

AccessibilityService

extends Service
java.lang.Object
   ↳ android.content.Context
     ↳ android.content.ContextWrapper
       ↳ android.app.Service
         ↳ android.accessibilityservice.AccessibilityService

Class Overview

An accessibility service runs in the background and receives callbacks by the system when AccessibilityEvents 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.

Developer Guides

For more information about creating AccessibilityServices, read the Accessibility developer guide.

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 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" Intent. Failure to declare this intent will cause the system to ignore the accessibility service. Additionally an accessibility service must request the BIND_ACCESSIBILITY_SERVICE permission to ensure that only the system can bind to it. Failure to declare this intent will cause the system to ignore the accessibility service. Following is an example declaration:

 <service android:name=".MyAccessibilityService"
         android:permission="android.permission.BIND_ACCESSIBILITY_SERVICE>
     <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:

  • Providing a meta-data entry in the manifest when declaring the service. A service declaration with a meta-data tag is presented below:
     <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>

    Note: This approach enables setting all properties.

    For more details refer to SERVICE_META_DATA and <accessibility-service>.

  • Calling setServiceInfo(AccessibilityServiceInfo). Note that this method can be called any time to dynamically change the service configuration.

    Note: This approach enables setting only dynamically configurable properties: eventTypes, feedbackType, flags, notificationTimeout, packageNames

    For more details refer to AccessibilityServiceInfo.

Retrieving window content

A service can specify in its declaration that it can retrieve the active window content which is represented as a tree of AccessibilityNodeInfo. Note that declaring this capability requires that the service declares its configuration via an XML resource referenced by 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: TYPE_WINDOW_STATE_CHANGED, TYPE_VIEW_HOVER_ENTER, 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 AccessibilityEvent.getSource() of the last received event of the above types or a previous event from the same window (see AccessibilityEvent.getWindowId()). Invoking this method will return an 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:

  • Register for all event types with no notification timeout and keep track for the active window by calling getWindowId() of the last received event and compare this with the getWindowId() before calling retrieval methods on the latter.
  • Prepare that a retrieval method on 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.

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

Summary

Constants
int GESTURE_SWIPE_DOWN The user has performed a swipe down gesture on the touch screen.
int GESTURE_SWIPE_DOWN_AND_LEFT The user has performed an down and left gesture on the touch screen.
int GESTURE_SWIPE_DOWN_AND_RIGHT The user has performed an down and right gesture on the touch screen.
int GESTURE_SWIPE_DOWN_AND_UP The user has performed a swipe down and up gesture on the touch screen.
int GESTURE_SWIPE_LEFT The user has performed a swipe left gesture on the touch screen.
int GESTURE_SWIPE_LEFT_AND_DOWN The user has performed a left and down gesture on the touch screen.
int GESTURE_SWIPE_LEFT_AND_RIGHT The user has performed a swipe left and right gesture on the touch screen.
int GESTURE_SWIPE_LEFT_AND_UP The user has performed a left and up gesture on the touch screen.
int GESTURE_SWIPE_RIGHT The user has performed a swipe right gesture on the touch screen.
int GESTURE_SWIPE_RIGHT_AND_DOWN The user has performed a right and down gesture on the touch screen.
int GESTURE_SWIPE_RIGHT_AND_LEFT The user has performed a swipe right and left gesture on the touch screen.
int GESTURE_SWIPE_RIGHT_AND_UP The user has performed a right and up gesture on the touch screen.
int GESTURE_SWIPE_UP The user has performed a swipe up gesture on the touch screen.
int GESTURE_SWIPE_UP_AND_DOWN The user has performed a swipe up and down gesture on the touch screen.
int GESTURE_SWIPE_UP_AND_LEFT The user has performed an up and left gesture on the touch screen.
int GESTURE_SWIPE_UP_AND_RIGHT The user has performed an up and right gesture on the touch screen.
int GLOBAL_ACTION_BACK Action to go back.
int GLOBAL_ACTION_HOME Action to go home.
int GLOBAL_ACTION_NOTIFICATIONS Action to open the notifications.
int GLOBAL_ACTION_RECENTS Action to open the recents.
String SERVICE_INTERFACE The Intent that must be declared as handled by the service.
String SERVICE_META_DATA Name under which an AccessibilityService component publishes information about itself.
[Expand]
Inherited Constants
From class android.app.Service
From class android.content.Context
From interface android.content.ComponentCallbacks2
Public Constructors
AccessibilityService()
Public Methods
AccessibilityNodeInfo getRootInActiveWindow()
Gets the root node in the currently active window if this service can retrieve window content.
final AccessibilityServiceInfo getServiceInfo()
Gets the an AccessibilityServiceInfo describing this AccessibilityService.
abstract void onAccessibilityEvent(AccessibilityEvent event)
Callback for AccessibilityEvents.
final IBinder onBind(Intent intent)
Implement to return the implementation of the internal accessibility service interface.
abstract void onInterrupt()
Callback for interrupting the accessibility feedback.
final boolean performGlobalAction(int action)
Performs a global action.
final void setServiceInfo(AccessibilityServiceInfo info)
Sets the AccessibilityServiceInfo that describes this service.
Protected Methods
boolean onGesture(int gestureId)
Called by the system when the user performs a specific gesture on the touch screen.
void onServiceConnected()
This method is a part of the AccessibilityService lifecycle and is called after the system has successfully bound to the service.
[Expand]
Inherited Methods
From class android.app.Service
From class android.content.ContextWrapper
From class android.content.Context
From class java.lang.Object
From interface android.content.ComponentCallbacks
From interface android.content.ComponentCallbacks2

Constants

public static final int GESTURE_SWIPE_DOWN

Since: API Level 16

The user has performed a swipe down gesture on the touch screen.

Constant Value: 2 (0x00000002)

public static final int GESTURE_SWIPE_DOWN_AND_LEFT

Since: API Level 16

The user has performed an down and left gesture on the touch screen.

Constant Value: 15 (0x0000000f)

public static final int GESTURE_SWIPE_DOWN_AND_RIGHT

Since: API Level 16

The user has performed an down and right gesture on the touch screen.

Constant Value: 16 (0x00000010)

public static final int GESTURE_SWIPE_DOWN_AND_UP

Since: API Level 16

The user has performed a swipe down and up gesture on the touch screen.

Constant Value: 8 (0x00000008)

public static final int GESTURE_SWIPE_LEFT

Since: API Level 16

The user has performed a swipe left gesture on the touch screen.

Constant Value: 3 (0x00000003)

public static final int GESTURE_SWIPE_LEFT_AND_DOWN

Since: API Level 16

The user has performed a left and down gesture on the touch screen.

Constant Value: 10 (0x0000000a)

public static final int GESTURE_SWIPE_LEFT_AND_RIGHT

Since: API Level 16

The user has performed a swipe left and right gesture on the touch screen.

Constant Value: 5 (0x00000005)

public static final int GESTURE_SWIPE_LEFT_AND_UP

Since: API Level 16

The user has performed a left and up gesture on the touch screen.

Constant Value: 9 (0x00000009)

public static final int GESTURE_SWIPE_RIGHT

Since: API Level 16

The user has performed a swipe right gesture on the touch screen.

Constant Value: 4 (0x00000004)

public static final int GESTURE_SWIPE_RIGHT_AND_DOWN

Since: API Level 16

The user has performed a right and down gesture on the touch screen.

Constant Value: 12 (0x0000000c)

public static final int GESTURE_SWIPE_RIGHT_AND_LEFT

Since: API Level 16

The user has performed a swipe right and left gesture on the touch screen.

Constant Value: 6 (0x00000006)

public static final int GESTURE_SWIPE_RIGHT_AND_UP

Since: API Level 16

The user has performed a right and up gesture on the touch screen.

Constant Value: 11 (0x0000000b)

public static final int GESTURE_SWIPE_UP

Since: API Level 16

The user has performed a swipe up gesture on the touch screen.

Constant Value: 1 (0x00000001)

public static final int GESTURE_SWIPE_UP_AND_DOWN

Since: API Level 16

The user has performed a swipe up and down gesture on the touch screen.

Constant Value: 7 (0x00000007)

public static final int GESTURE_SWIPE_UP_AND_LEFT

Since: API Level 16

The user has performed an up and left gesture on the touch screen.

Constant Value: 13 (0x0000000d)

public static final int GESTURE_SWIPE_UP_AND_RIGHT

Since: API Level 16

The user has performed an up and right gesture on the touch screen.

Constant Value: 14 (0x0000000e)

public static final int GLOBAL_ACTION_BACK

Since: API Level 16

Action to go back.

Constant Value: 1 (0x00000001)

public static final int GLOBAL_ACTION_HOME

Since: API Level 16

Action to go home.

Constant Value: 2 (0x00000002)

public static final int GLOBAL_ACTION_NOTIFICATIONS

Since: API Level 16

Action to open the notifications.

Constant Value: 4 (0x00000004)

public static final int GLOBAL_ACTION_RECENTS

Since: API Level 16

Action to open the recents.

Constant Value: 3 (0x00000003)

public static final String SERVICE_INTERFACE

Since: API Level 4

The Intent that must be declared as handled by the service.

Constant Value: "android.accessibilityservice.AccessibilityService"

public static final String SERVICE_META_DATA

Since: API Level 14

Name under which an AccessibilityService component publishes information about itself. This meta-data must reference an XML resource containing an <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"
     . . .
 />

Constant Value: "android.accessibilityservice"

Public Constructors

public AccessibilityService ()

Since: API Level 4

Public Methods

public AccessibilityNodeInfo getRootInActiveWindow ()

Since: API Level 16

Gets the root node in the currently active window if this service can retrieve window content.

Returns
  • The root node if this service can retrieve window content.

public final AccessibilityServiceInfo getServiceInfo ()

Since: API Level 16

Gets the an AccessibilityServiceInfo describing this AccessibilityService. This method is useful if one wants to change some of the dynamically configurable properties at runtime.

Returns
  • The accessibility service info.

public abstract void onAccessibilityEvent (AccessibilityEvent event)

Since: API Level 4

Callback for AccessibilityEvents.

Parameters
event An event.

public final IBinder onBind (Intent intent)

Since: API Level 4

Implement to return the implementation of the internal accessibility service interface.

Parameters
intent The Intent that was used to bind to this service, as given to Context.bindService. Note that any extras that were included with the Intent at that point will not be seen here.
Returns
  • Return an IBinder through which clients can call on to the service.

public abstract void onInterrupt ()

Since: API Level 4

Callback for interrupting the accessibility feedback.

public final boolean performGlobalAction (int action)

Since: API Level 16

Performs a global action. Such an action can be performed at any moment regardless of the current application or user location in that application. For example going back, going home, opening recents, etc.

Parameters
action The action to perform.
Returns
  • Whether the action was successfully performed.

public final void setServiceInfo (AccessibilityServiceInfo info)

Since: API Level 4

Sets the 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.

Parameters
info The info.

Protected Methods

protected boolean onGesture (int gestureId)

Since: API Level 16

Called by the system when the user performs a specific gesture on the touch screen. Note: To receive gestures an accessibility service must request that the device is in touch exploration mode by setting the FLAG_REQUEST_TOUCH_EXPLORATION_MODE flag.

Parameters
gestureId The unique id of the performed gesture.
Returns
  • Whether the gesture was handled.

protected void onServiceConnected ()

Since: API Level 4

This method is a part of the AccessibilityService lifecycle and is called after the system has successfully bound to the service. If is convenient to use this method for setting the AccessibilityServiceInfo.