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loic-sharmaloic-sharma
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[Windows] Introduce an accessibility plugin (#50975)
_This is the same pull request as #50898. GitHub broke on the previous pull request so I re-created it_ This moves the logic to handle `flutter/accessibility` messages to a new type, `AccessibilityPlugin`. Notable changes: 1. Windows app no longer crashes if it receives accessibility events it does not support 2. Windows app no longer crashes if it receives accessibility events while in headless mode @yaakovschectman After playing around with this, I ended up using a different pattern than what what I suggested on #50598 (comment). This message handler is simple enough that splitting into a child/base types felt like unnecessary boilerplate. The key thing is separating messaging and implementation logic, which was achieved through the `SetUp` method. Let me know what you think, and sorry for all my flip-flopping on this topic! � This is preparation for: flutter/flutter#143765 Sample app for manual testing: flutter/flutter#113059 [C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style
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‎ci/licenses_golden/licenses_flutter‎

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@@ -29967,6 +29967,8 @@ ORIGIN: ../../../flutter/shell/platform/linux/public/flutter_linux/fl_view.h + .
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ORIGIN: ../../../flutter/shell/platform/linux/public/flutter_linux/flutter_linux.h + ../../../flutter/LICENSE
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ORIGIN: ../../../flutter/shell/platform/windows/accessibility_bridge_windows.cc + ../../../flutter/LICENSE
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ORIGIN: ../../../flutter/shell/platform/windows/accessibility_bridge_windows.h + ../../../flutter/LICENSE
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ORIGIN: ../../../flutter/shell/platform/windows/accessibility_plugin.cc + ../../../flutter/LICENSE
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ORIGIN: ../../../flutter/shell/platform/windows/accessibility_plugin.h + ../../../flutter/LICENSE
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ORIGIN: ../../../flutter/shell/platform/windows/client_wrapper/flutter_engine.cc + ../../../flutter/LICENSE
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ORIGIN: ../../../flutter/shell/platform/windows/client_wrapper/flutter_view_controller.cc + ../../../flutter/LICENSE
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ORIGIN: ../../../flutter/shell/platform/windows/client_wrapper/include/flutter/dart_project.h + ../../../flutter/LICENSE
@@ -32840,6 +32842,8 @@ FILE: ../../../flutter/shell/platform/linux/public/flutter_linux/fl_view.h
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FILE: ../../../flutter/shell/platform/linux/public/flutter_linux/flutter_linux.h
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FILE: ../../../flutter/shell/platform/windows/accessibility_bridge_windows.cc
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FILE: ../../../flutter/shell/platform/windows/accessibility_bridge_windows.h
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FILE: ../../../flutter/shell/platform/windows/accessibility_plugin.cc
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FILE: ../../../flutter/shell/platform/windows/accessibility_plugin.h
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FILE: ../../../flutter/shell/platform/windows/client_wrapper/flutter_engine.cc
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FILE: ../../../flutter/shell/platform/windows/client_wrapper/flutter_view_controller.cc
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FILE: ../../../flutter/shell/platform/windows/client_wrapper/include/flutter/dart_project.h

‎shell/platform/windows/BUILD.gn‎

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@@ -41,6 +41,8 @@ source_set("flutter_windows_source") {
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sources = [
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"accessibility_bridge_windows.cc",
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"accessibility_bridge_windows.h",
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"accessibility_plugin.cc",
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"accessibility_plugin.h",
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"compositor.h",
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"compositor_opengl.cc",
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"compositor_opengl.h",

‎shell/platform/windows/accessibility_plugin.cc‎

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// Copyright 2013 The Flutter Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#include "flutter/shell/platform/windows/accessibility_plugin.h"
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#include <variant>
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#include "flutter/fml/logging.h"
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#include "flutter/fml/platform/win/wstring_conversion.h"
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#include "flutter/shell/platform/common/client_wrapper/include/flutter/standard_message_codec.h"
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#include "flutter/shell/platform/windows/flutter_windows_engine.h"
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#include "flutter/shell/platform/windows/flutter_windows_view.h"
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namespace flutter {
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namespace {
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static constexpr char kAccessibilityChannelName[] = "flutter/accessibility";
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static constexpr char kTypeKey[] = "type";
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static constexpr char kDataKey[] = "data";
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static constexpr char kMessageKey[] = "message";
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static constexpr char kAnnounceValue[] = "announce";
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// Handles messages like:
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// {"type": "announce", "data": {"message": "Hello"}}
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void HandleMessage(AccessibilityPlugin* plugin, const EncodableValue& message) {
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const auto* map = std::get_if<EncodableMap>(&message);
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if (!map) {
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FML_LOG(ERROR) << "Accessibility message must be a map.";
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return;
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}
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const auto& type_itr = map->find(EncodableValue{kTypeKey});
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const auto& data_itr = map->find(EncodableValue{kDataKey});
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if (type_itr == map->end()) {
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FML_LOG(ERROR) << "Accessibility message must have a 'type' property.";
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return;
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}
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if (data_itr == map->end()) {
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FML_LOG(ERROR) << "Accessibility message must have a 'data' property.";
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return;
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}
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const auto* type = std::get_if<std::string>(&type_itr->second);
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const auto* data = std::get_if<EncodableMap>(&data_itr->second);
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if (!type) {
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FML_LOG(ERROR) << "Accessibility message 'type' property must be a string.";
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return;
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}
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if (!data) {
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FML_LOG(ERROR) << "Accessibility message 'data' property must be a map.";
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return;
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}
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if (type->compare(kAnnounceValue) == 0) {
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const auto& message_itr = data->find(EncodableValue{kMessageKey});
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if (message_itr == data->end()) {
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return;
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}
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const auto* message = std::get_if<std::string>(&message_itr->second);
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if (!message) {
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return;
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}
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plugin->Announce(*message);
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} else {
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FML_LOG(ERROR) << "Accessibility message type '" << *type
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<< "' is not supported.";
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}
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}
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} // namespace
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AccessibilityPlugin::AccessibilityPlugin(FlutterWindowsEngine* engine)
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: engine_(engine) {}
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void AccessibilityPlugin::SetUp(BinaryMessenger* binary_messenger,
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AccessibilityPlugin* plugin) {
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BasicMessageChannel<> channel{binary_messenger, kAccessibilityChannelName,
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&StandardMessageCodec::GetInstance()};
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channel.SetMessageHandler(
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[plugin](const EncodableValue& message,
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const MessageReply<EncodableValue>& reply) {
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HandleMessage(plugin, message);
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// The accessibility channel does not support error handling.
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// Always return an empty response even on failure.
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reply(EncodableValue{std::monostate{}});
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});
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}
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void AccessibilityPlugin::Announce(const std::string_view message) {
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if (!engine_->semantics_enabled()) {
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return;
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}
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// TODO(loicsharma): Remove implicit view assumption.
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// https://github.com/flutter/flutter/issues/142845
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auto view = engine_->view(kImplicitViewId);
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if (!view) {
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return;
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}
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std::wstring wide_text = fml::Utf8ToWideString(message);
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view->AnnounceAlert(wide_text);
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}
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} // namespace flutter

‎shell/platform/windows/accessibility_plugin.h‎

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// Copyright 2013 The Flutter Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef FLUTTER_SHELL_PLATFORM_WINDOWS_ACCESSIBILITY_PLUGIN_H_
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#define FLUTTER_SHELL_PLATFORM_WINDOWS_ACCESSIBILITY_PLUGIN_H_
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#include <string_view>
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#include "flutter/fml/macros.h"
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#include "flutter/shell/platform/common/client_wrapper/include/flutter/binary_messenger.h"
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namespace flutter {
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class FlutterWindowsEngine;
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// Handles messages on the flutter/accessibility channel.
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//
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// See:
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// https://api.flutter.dev/flutter/semantics/SemanticsService-class.html
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class AccessibilityPlugin {
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public:
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explicit AccessibilityPlugin(FlutterWindowsEngine* engine);
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// Begin handling accessibility messages on the `binary_messenger`.
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static void SetUp(BinaryMessenger* binary_messenger,
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AccessibilityPlugin* plugin);
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// Announce a message through the assistive technology.
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virtual void Announce(const std::string_view message);
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private:
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// The engine that owns this plugin.
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FlutterWindowsEngine* engine_ = nullptr;
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FML_DISALLOW_COPY_AND_ASSIGN(AccessibilityPlugin);
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};
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} // namespace flutter
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#endif // FLUTTER_SHELL_PLATFORM_WINDOWS_ACCESSIBILITY_PLUGIN_H_

‎shell/platform/windows/fixtures/main.dart‎

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@@ -59,36 +59,65 @@ void sendAccessibilityAnnouncement() async {
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await semanticsChanged;
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}
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62-
// Serializers for data types are in the framework, so this will be hardcoded.
62+
// Standard message codec magic number identifiers.
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// See: https://github.com/flutter/flutter/blob/ee94fe262b63b0761e8e1f889ae52322fef068d2/packages/flutter/lib/src/services/message_codecs.dart#L262
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const int valueMap = 13, valueString = 7;
64-
// Corresponds to:
65-
// Map<String, Object> data =
66-
// {"type": "announce", "data": {"message": ""}};
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66+
// Corresponds to: {"type": "announce", "data": {"message": "hello"}}
67+
// See: https://github.com/flutter/flutter/blob/b781da9b5822de1461a769c3b245075359f5464d/packages/flutter/lib/src/semantics/semantics_event.dart#L86
68+
final Uint8List data = Uint8List.fromList([
69+
// Map with 2 entries
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valueMap, 2,
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// Map key: "type"
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valueString, 'type'.length, ...'type'.codeUnits,
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// Map value: "announce"
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valueString, 'announce'.length, ...'announce'.codeUnits,
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// Map key: "data"
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valueString, 'data'.length, ...'data'.codeUnits,
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// Map value: map with 1 entry
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valueMap, 1,
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// Map key: "message"
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valueString, 'message'.length, ...'message'.codeUnits,
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// Map value: "hello"
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valueString, 'hello'.length, ...'hello'.codeUnits,
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]);
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final ByteData byteData = data.buffer.asByteData();
85+
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ui.PlatformDispatcher.instance.sendPlatformMessage(
87+
'flutter/accessibility',
88+
byteData,
89+
(ByteData? _) => signal(),
90+
);
91+
}
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93+
@pragma('vm:entry-point')
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void sendAccessibilityTooltipEvent() async {
95+
// Wait until semantics are enabled.
96+
if (!ui.PlatformDispatcher.instance.semanticsEnabled) {
97+
await semanticsChanged;
98+
}
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// Standard message codec magic number identifiers.
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// See: https://github.com/flutter/flutter/blob/ee94fe262b63b0761e8e1f889ae52322fef068d2/packages/flutter/lib/src/services/message_codecs.dart#L262
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const int valueMap = 13, valueString = 7;
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// Corresponds to: {"type": "tooltip", "data": {"message": "hello"}}
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// See: https://github.com/flutter/flutter/blob/b781da9b5822de1461a769c3b245075359f5464d/packages/flutter/lib/src/semantics/semantics_event.dart#L120
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final Uint8List data = Uint8List.fromList([
68-
valueMap, // _valueMap
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2, // Size
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// key: "type"
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valueString,
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'type'.length,
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...'type'.codeUnits,
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// value: "announce"
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valueString,
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'announce'.length,
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...'announce'.codeUnits,
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// key: "data"
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valueString,
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'data'.length,
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...'data'.codeUnits,
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// value: map
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valueMap, // _valueMap
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1, // Size
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// key: "message"
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valueString,
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'message'.length,
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...'message'.codeUnits,
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// value: ""
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valueString,
91-
0, // Length of empty string == 0.
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// Map with 2 entries
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valueMap, 2,
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// Map key: "type"
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valueString, 'type'.length, ...'type'.codeUnits,
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// Map value: "tooltip"
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valueString, 'tooltip'.length, ...'tooltip'.codeUnits,
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// Map key: "data"
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valueString, 'data'.length, ...'data'.codeUnits,
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// Map value: map with 1 entry
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valueMap, 1,
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// Map key: "message"
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valueString, 'message'.length, ...'message'.codeUnits,
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// Map value: "hello"
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valueString, 'hello'.length, ...'hello'.codeUnits,
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]);
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final ByteData byteData = data.buffer.asByteData();
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‎shell/platform/windows/flutter_windows_engine.cc‎

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std::make_unique<BinaryMessengerImpl>(messenger_->ToRef());
184184
message_dispatcher_ =
185185
std::make_unique<IncomingMessageDispatcher>(messenger_->ToRef());
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message_dispatcher_->SetMessageCallback(
187-
kAccessibilityChannelName,
188-
[](FlutterDesktopMessengerRef messenger,
189-
const FlutterDesktopMessage* message, void* data) {
190-
FlutterWindowsEngine* engine = static_cast<FlutterWindowsEngine*>(data);
191-
engine->HandleAccessibilityMessage(messenger, message);
192-
},
193-
static_cast<void*>(this));
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195187
texture_registrar_ =
196188
std::make_unique<FlutterWindowsTextureRegistrar>(this, gl_);
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// https://github.com/flutter/flutter/issues/71099
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internal_plugin_registrar_ =
221213
std::make_unique<PluginRegistrar>(plugin_registrar_.get());
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215+
accessibility_plugin_ = std::make_unique<AccessibilityPlugin>(this);
216+
AccessibilityPlugin::SetUp(messenger_wrapper_.get(),
217+
accessibility_plugin_.get());
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cursor_handler_ =
223220
std::make_unique<CursorHandler>(messenger_wrapper_.get(), this);
224221
platform_handler_ =
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765762
if (engine_ && semantics_enabled_ != enabled) {
766763
semantics_enabled_ = enabled;
767764
embedder_api_.UpdateSemanticsEnabled(engine_, enabled);
768-
view_->UpdateSemanticsEnabled(enabled);
765+
if (view_) {
766+
view_->UpdateSemanticsEnabled(enabled);
767+
}
769768
}
770769
}
771770

@@ -813,27 +812,6 @@ void FlutterWindowsEngine::SendAccessibilityFeatures() {
813812
engine_, static_cast<FlutterAccessibilityFeature>(flags));
814813
}
815814

816-
void FlutterWindowsEngine::HandleAccessibilityMessage(
817-
FlutterDesktopMessengerRef messenger,
818-
const FlutterDesktopMessage* message) {
819-
const auto& codec = StandardMessageCodec::GetInstance();
820-
auto data = codec.DecodeMessage(message->message, message->message_size);
821-
EncodableMap map = std::get<EncodableMap>(*data);
822-
std::string type = std::get<std::string>(map.at(EncodableValue("type")));
823-
if (type.compare("announce") == 0) {
824-
if (semantics_enabled_) {
825-
EncodableMap data_map =
826-
std::get<EncodableMap>(map.at(EncodableValue("data")));
827-
std::string text =
828-
std::get<std::string>(data_map.at(EncodableValue("message")));
829-
std::wstring wide_text = fml::Utf8ToWideString(text);
830-
view_->AnnounceAlert(wide_text);
831-
}
832-
}
833-
SendPlatformMessageResponse(message->response_handle,
834-
reinterpret_cast<const uint8_t*>(""), 0);
835-
}
836-
837815
void FlutterWindowsEngine::RequestApplicationQuit(HWND hwnd,
838816
WPARAM wparam,
839817
LPARAM lparam,

‎shell/platform/windows/flutter_windows_engine.h‎

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Original file line numberDiff line numberDiff line change
@@ -22,6 +22,7 @@
2222
#include "flutter/shell/platform/common/incoming_message_dispatcher.h"
2323
#include "flutter/shell/platform/embedder/embedder.h"
2424
#include "flutter/shell/platform/windows/accessibility_bridge_windows.h"
25+
#include "flutter/shell/platform/windows/accessibility_plugin.h"
2526
#include "flutter/shell/platform/windows/compositor.h"
2627
#include "flutter/shell/platform/windows/cursor_handler.h"
2728
#include "flutter/shell/platform/windows/egl/manager.h"
@@ -338,9 +339,6 @@ class FlutterWindowsEngine {
338339
// Send the currently enabled accessibility features to the engine.
339340
void SendAccessibilityFeatures();
340341

341-
void HandleAccessibilityMessage(FlutterDesktopMessengerRef messenger,
342-
const FlutterDesktopMessage* message);
343-
344342
// The handle to the embedder.h engine instance.
345343
FLUTTER_API_SYMBOL(FlutterEngine) engine_ = nullptr;
346344

@@ -384,6 +382,9 @@ class FlutterWindowsEngine {
384382
// The plugin registrar managing internal plugins.
385383
std::unique_ptr<PluginRegistrar> internal_plugin_registrar_;
386384

385+
// Handler for accessibility events.
386+
std::unique_ptr<AccessibilityPlugin> accessibility_plugin_;
387+
387388
// Handler for cursor events.
388389
std::unique_ptr<CursorHandler> cursor_handler_;
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