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// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
import 'package:flute/foundation.dart';
import 'package:flute/painting.dart';
export 'package:engine/ui.dart' show TextDirection;
/// Determines the assertiveness level of the accessibility announcement.
///
/// It is used by [AnnounceSemanticsEvent] to determine the priority with which
/// assistive technology should treat announcements.
enum Assertiveness {
/// The assistive technology will speak changes whenever the user is idle.
polite,
/// The assistive technology will interrupt any announcement that it is
/// currently making to notify the user about the change.
///
/// It should only be used for time-sensitive/critical notifications.
assertive,
}
/// An event sent by the application to notify interested listeners that
/// something happened to the user interface (e.g. a view scrolled).
///
/// These events are usually interpreted by assistive technologies to give the
/// user additional clues about the current state of the UI.
abstract class SemanticsEvent {
/// Initializes internal fields.
///
/// [type] is a string that identifies this class of [SemanticsEvent]s.
const SemanticsEvent(this.type);
/// The type of this event.
///
/// The type is used by the engine to translate this event into the
/// appropriate native event (`UIAccessibility*Notification` on iOS and
/// `AccessibilityEvent` on Android).
final String type;
/// Converts this event to a Map that can be encoded with
/// [StandardMessageCodec].
///
/// [nodeId] is the unique identifier of the semantics node associated with
/// the event, or null if the event is not associated with a semantics node.
Map<String, dynamic> toMap({ int? nodeId }) {
final Map<String, dynamic> event = <String, dynamic>{
'type': type,
'data': getDataMap(),
};
if (nodeId != null) {
event['nodeId'] = nodeId;
}
return event;
}
/// Returns the event's data object.
Map<String, dynamic> getDataMap();
@override
String toString() {
final List<String> pairs = <String>[];
final Map<String, dynamic> dataMap = getDataMap();
final List<String> sortedKeys = dataMap.keys.toList()..sort();
for (final String key in sortedKeys) {
pairs.add('$key: ${dataMap[key]}');
}
return '${objectRuntimeType(this, 'SemanticsEvent')}(${pairs.join(', ')})';
}
}
/// An event for a semantic announcement.
///
/// This should be used for announcement that are not seamlessly announced by
/// the system as a result of a UI state change.
///
/// For example a camera application can use this method to make accessibility
/// announcements regarding objects in the viewfinder.
///
/// When possible, prefer using mechanisms like [Semantics] to implicitly
/// trigger announcements over using this event.
class AnnounceSemanticsEvent extends SemanticsEvent {
/// Constructs an event that triggers an announcement by the platform.
const AnnounceSemanticsEvent(this.message, this.textDirection, {this.assertiveness = Assertiveness.polite})
: super('announce');
/// The message to announce.
///
/// This property must not be null.
final String message;
/// Text direction for [message].
///
/// This property must not be null.
final TextDirection textDirection;
/// Determines whether the announcement should interrupt any existing announcement,
/// or queue after it.
///
/// On the web this option uses the aria-live level to set the assertiveness
/// of the announcement. On iOS, Android, Windows, Linux, macOS, and Fuchsia
/// this option currently has no effect.
final Assertiveness assertiveness;
@override
Map<String, dynamic> getDataMap() {
return <String, dynamic> {
'message': message,
'textDirection': textDirection.index,
if (assertiveness != Assertiveness.polite)
'assertiveness': assertiveness.index,
};
}
}
/// An event for a semantic announcement of a tooltip.
///
/// This is only used by Android to announce tooltip values.
class TooltipSemanticsEvent extends SemanticsEvent {
/// Constructs an event that triggers a tooltip announcement by the platform.
const TooltipSemanticsEvent(this.message) : super('tooltip');
/// The text content of the tooltip.
final String message;
@override
Map<String, dynamic> getDataMap() {
return <String, dynamic>{
'message': message,
};
}
}
/// An event which triggers long press semantic feedback.
///
/// Currently only honored on Android. Triggers a long-press specific sound
/// when TalkBack is enabled.
class LongPressSemanticsEvent extends SemanticsEvent {
/// Constructs an event that triggers a long-press semantic feedback by the platform.
const LongPressSemanticsEvent() : super('longPress');
@override
Map<String, dynamic> getDataMap() => const <String, dynamic>{};
}
/// An event which triggers tap semantic feedback.
///
/// Currently only honored on Android. Triggers a tap specific sound when
/// TalkBack is enabled.
class TapSemanticEvent extends SemanticsEvent {
/// Constructs an event that triggers a long-press semantic feedback by the platform.
const TapSemanticEvent() : super('tap');
@override
Map<String, dynamic> getDataMap() => const <String, dynamic>{};
}