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[Windows] Introduce an accessibility plugin #50898
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| Original file line number | Diff line number | Diff line change |
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| // Copyright 2013 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. | ||
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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/platform/win/wstring_conversion.h" | ||
| #include "flutter/shell/platform/common/client_wrapper/include/flutter/standard_message_codec.h" | ||
| #include "flutter/shell/platform/windows/flutter_windows_engine.h" | ||
| #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"; | ||
| static constexpr char kTypeKey[] = "type"; | ||
| static constexpr char kDataKey[] = "data"; | ||
| static constexpr char kMessageKey[] = "message"; | ||
| static constexpr char kAnnounceValue[] = "announce"; | ||
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| // Handles messages like: | ||
| // {"type": "announce", "data": {"message": "Hello"}} | ||
| void HandleMessage(AccessibilityPlugin* plugin, const EncodableValue& message) { | ||
| const auto* map = std::get_if<EncodableMap>(&message); | ||
| if (!map) { | ||
| return; | ||
| } | ||
| const auto& type_itr = map->find(EncodableValue{kTypeKey}); | ||
| const auto& data_itr = map->find(EncodableValue{kDataKey}); | ||
| if (type_itr == map->end() || data_itr == map->end()) { | ||
| return; | ||
| } | ||
| const auto* type = std::get_if<std::string>(&type_itr->second); | ||
| const auto* data = std::get_if<EncodableMap>(&data_itr->second); | ||
| if (!type || !data) { | ||
| return; | ||
| } | ||
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| if (type->compare(kAnnounceValue) == 0) { | ||
| const auto& message_itr = data->find(EncodableValue{kMessageKey}); | ||
| if (message_itr == data->end()) { | ||
| return; | ||
| } | ||
| const auto* message = std::get_if<std::string>(&message_itr->second); | ||
| if (!message) { | ||
| return; | ||
| } | ||
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| plugin->Announce(*message); | ||
| } | ||
| } | ||
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| } // namespace | ||
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| AccessibilityPlugin::AccessibilityPlugin(FlutterWindowsEngine* engine) | ||
| : engine_(engine) {} | ||
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| void AccessibilityPlugin::SetUp(BinaryMessenger* binary_messenger, | ||
| AccessibilityPlugin* plugin) { | ||
| BasicMessageChannel<> channel{binary_messenger, kAccessibilityChannelName, | ||
| &StandardMessageCodec::GetInstance()}; | ||
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| channel.SetMessageHandler( | ||
| [plugin](const EncodableValue& message, | ||
| const MessageReply<EncodableValue>& reply) { | ||
| HandleMessage(plugin, message); | ||
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| // The accessibility channel does not support error handling. | ||
| // Always return an empty response even on failure. | ||
| reply(EncodableValue{std::monostate{}}); | ||
| }); | ||
| } | ||
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| void AccessibilityPlugin::Announce(const std::string_view message) { | ||
| if (!engine_->semantics_enabled()) { | ||
| return; | ||
| } | ||
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| // TODO(loicsharma): Remove implicit view assumption. | ||
| // https://github.com/flutter/flutter/issues/142845 | ||
| auto view = engine_->view(kImplicitViewId); | ||
| if (!view) { | ||
| return; | ||
| } | ||
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| std::wstring wide_text = fml::Utf8ToWideString(message); | ||
| view->AnnounceAlert(wide_text); | ||
| } | ||
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| } // namespace flutter | ||
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,41 @@ | ||
| // Copyright 2013 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. | ||
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| #ifndef FLUTTER_SHELL_PLATFORM_WINDOWS_ACCESSIBILITY_PLUGIN_H_ | ||
| #define FLUTTER_SHELL_PLATFORM_WINDOWS_ACCESSIBILITY_PLUGIN_H_ | ||
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| #include <string_view> | ||
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| #include "flutter/fml/macros.h" | ||
| #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. | ||
| // | ||
| // See: | ||
| // https://api.flutter.dev/flutter/semantics/SemanticsService-class.html | ||
| class AccessibilityPlugin { | ||
| public: | ||
| explicit AccessibilityPlugin(FlutterWindowsEngine* engine); | ||
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| // Begin handling accessibility messages on the `binary_messenger`. | ||
| static void SetUp(BinaryMessenger* binary_messenger, | ||
| AccessibilityPlugin* plugin); | ||
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| // Announce a message through the assistive technology. | ||
| virtual void Announce(const std::string_view message); | ||
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| private: | ||
| // The engine that owns this plugin. | ||
| FlutterWindowsEngine* engine_ = nullptr; | ||
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| FML_DISALLOW_COPY_AND_ASSIGN(AccessibilityPlugin); | ||
| }; | ||
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| } // namespace flutter | ||
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| #endif // FLUTTER_SHELL_PLATFORM_WINDOWS_ACCESSIBILITY_PLUGIN_H_ |
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Should this produce an error if type or data is missing?
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I'm not sure why, but the
flutter/accessibilitychannel does not follow the normal method call protocol. AFAICT it does not support error handling. Ignoring malformed messages appears to be the "correct" implementation:null.true.There was a problem hiding this comment.
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Would we want to log an error message? Or just ignore it if the other platforms do so?
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Excellent idea, added!
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Hmm, GitHub seems to be broken... it isn't showing the latest commit... I tried force pushing my changes too 🙃
You can find the latest implementation here: https://github.com/loic-sharma/flutter-engine/blob/c5be9d79e3c55835ece522bd8e3b8261ee19f529/shell/platform/windows/accessibility_plugin.cc#L27-L69