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.