Package io.flutter.embedding.engine.systemchannels

Class AccessibilityChannel

java.lang.Object

io.flutter.embedding.engine.systemchannels.AccessibilityChannel

public class AccessibilityChannel
extends Object

System channel that sends accessibility requests and events from Flutter to Android.

See AccessibilityChannel.AccessibilityMessageHandler, which lists all accessibility requests and events that might be sent from Flutter to the Android platform.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static interface	AccessibilityChannel.AccessibilityMessageHandler	Handler that receives accessibility messages sent from Flutter to Android through a given AccessibilityChannel.

Field Summary

Fields

Modifier and Type	Field	Description
final BasicMessageChannel<Object>	channel
final FlutterJNI	flutterJNI
final BasicMessageChannel.MessageHandler<Object>	parsingMessageHandler

Constructor Summary

Constructors

Constructor	Description
AccessibilityChannel(DartExecutor dartExecutor, FlutterJNI flutterJNI)	Constructs an AccessibilityChannel that connects Android to the Dart code running in dartExecutor.
AccessibilityChannel(BasicMessageChannel<Object> channel, FlutterJNI flutterJNI)

Method Summary

Modifier and Type	Method	Description
void	dispatchSemanticsAction(int virtualViewId, AccessibilityBridge.Action action)	Instructs Flutter to perform the given action on the SemanticsNode referenced by the given virtualViewId.
void	dispatchSemanticsAction(int virtualViewId, AccessibilityBridge.Action action, Object args)	Instructs Flutter to perform the given action on the SemanticsNode referenced by the given virtualViewId, passing the given args.
void	onAndroidAccessibilityDisabled()	Informs Flutter that the Android OS currently has accessibility disabled.
void	onAndroidAccessibilityEnabled()	Informs Flutter that the Android OS currently has accessibility enabled.
void	setAccessibilityFeatures(int accessibilityFeatureFlags)	Instructs Flutter to activate/deactivate accessibility features corresponding to the flags provided by accessibilityFeatureFlags.
void	setAccessibilityMessageHandler(AccessibilityChannel.AccessibilityMessageHandler handler)	Sets the AccessibilityChannel.AccessibilityMessageHandler which receives all events and requests that are parsed from the underlying accessibility channel.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

channel

@NonNull
public final BasicMessageChannel<Object> channel

flutterJNI

@NonNull
public final FlutterJNI flutterJNI

parsingMessageHandler

public final BasicMessageChannel.MessageHandler<Object> parsingMessageHandler

Constructor Details

AccessibilityChannel

public AccessibilityChannel(@NonNull
 DartExecutor dartExecutor,
 @NonNull
 FlutterJNI flutterJNI)

Constructs an AccessibilityChannel that connects Android to the Dart code running in dartExecutor.

The given dartExecutor is permitted to be idle or executing code.

See DartExecutor.

AccessibilityChannel

@VisibleForTesting
public AccessibilityChannel(@NonNull
 BasicMessageChannel<Object> channel,
 @NonNull
 FlutterJNI flutterJNI)

Method Details

onAndroidAccessibilityEnabled

public void onAndroidAccessibilityEnabled()

Informs Flutter that the Android OS currently has accessibility enabled.

To accommodate enabled accessibility, this method instructs Flutter to activate its semantics tree, which forms the basis of Flutter's accessibility support.

onAndroidAccessibilityDisabled

public void onAndroidAccessibilityDisabled()

Informs Flutter that the Android OS currently has accessibility disabled.

Given that accessibility is not required at this time, this method instructs Flutter to deactivate its semantics tree.

setAccessibilityFeatures

public void setAccessibilityFeatures(int accessibilityFeatureFlags)

Instructs Flutter to activate/deactivate accessibility features corresponding to the flags provided by accessibilityFeatureFlags.

dispatchSemanticsAction

public void dispatchSemanticsAction(int virtualViewId,
 @NonNull
 AccessibilityBridge.Action action)

Instructs Flutter to perform the given action on the SemanticsNode referenced by the given virtualViewId.

One might wonder why Flutter would need to be instructed that the user wants to perform an action. When the user is touching the screen in accessibility mode, Android takes over the touch input, categorizing input as one of a many accessibility gestures. Therefore, Flutter does not have an opportunity to react to said touch input. Instead, Flutter must be notified by Android of the desired action. Additionally, some accessibility systems use other input methods, such as speech, to take virtual actions. Android interprets those requests and then instructs the app to take the appropriate action.

dispatchSemanticsAction

public void dispatchSemanticsAction(int virtualViewId,
 @NonNull
 AccessibilityBridge.Action action,
 @Nullable
 Object args)

Instructs Flutter to perform the given action on the SemanticsNode referenced by the given virtualViewId, passing the given args.

setAccessibilityMessageHandler

public void setAccessibilityMessageHandler(@Nullable
 AccessibilityChannel.AccessibilityMessageHandler handler)

Sets the AccessibilityChannel.AccessibilityMessageHandler which receives all events and requests that are parsed from the underlying accessibility channel.