accessibility_bridge.h

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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.
 
#ifndef FLUTTER_SHELL_PLATFORM_COMMON_ACCESSIBILITY_BRIDGE_H_
#define FLUTTER_SHELL_PLATFORM_COMMON_ACCESSIBILITY_BRIDGE_H_
 
#include <unordered_map>
 
#include "flutter/fml/mapping.h"
#include "flutter/shell/platform/embedder/embedder.h"
 
#include "flutter/third_party/accessibility/ax/ax_event_generator.h"
#include "flutter/third_party/accessibility/ax/ax_tree.h"
#include "flutter/third_party/accessibility/ax/ax_tree_observer.h"
#include "flutter/third_party/accessibility/ax/platform/ax_platform_node_delegate.h"
#include "flutter/third_party/accessibility/ax/platform/ax_platform_tree_manager.h"
 
#include "flutter_platform_node_delegate.h"
 
namespace flutter {
 
//------------------------------------------------------------------------------
/// Use this class to maintain an accessibility tree. This class consumes
/// semantics updates from the embedder API and produces an accessibility tree
/// in the native format.
///
/// The bridge creates an AXTree to hold the semantics data that comes from
/// Flutter semantics updates. The tree holds AXNode[s] which contain the
/// semantics information for semantics node. The AXTree resemble the Flutter
/// semantics tree in the Flutter framework. The bridge also uses
/// FlutterPlatformNodeDelegate to wrap each AXNode in order to provide
/// an accessibility tree in the native format.
///
/// To use this class, one must subclass this class and provide their own
/// implementation of FlutterPlatformNodeDelegate.
///
/// AccessibilityBridge must be created as a shared_ptr, since some methods
/// acquires its weak_ptr.
class AccessibilityBridge
    : public std::enable_shared_from_this<AccessibilityBridge>,
      public FlutterPlatformNodeDelegate::OwnerBridge,
      public ui::AXPlatformTreeManager,
      private ui::AXTreeObserver {
 public:
  //-----------------------------------------------------------------------------
  /// @brief      Creates a new instance of a accessibility bridge.
  AccessibilityBridge();
  virtual ~AccessibilityBridge();
 
  //------------------------------------------------------------------------------
  /// @brief      Adds a semantics node update to the pending semantics update.
  ///             Calling this method alone will NOT update the semantics tree.
  ///             To flush the pending updates, call the CommitUpdates().
  ///
  /// @param[in]  node           A reference to the semantics node update.
  void AddFlutterSemanticsNodeUpdate(const FlutterSemanticsNode2& node);
 
  //------------------------------------------------------------------------------
  /// @brief      Adds a custom semantics action update to the pending semantics
  ///             update. Calling this method alone will NOT update the
  ///             semantics tree. To flush the pending updates, call the
  ///             CommitUpdates().
  ///
  /// @param[in]  action           A reference to the custom semantics action
  ///                              update.
  void AddFlutterSemanticsCustomActionUpdate(
      const FlutterSemanticsCustomAction2& action);
 
  //------------------------------------------------------------------------------
  /// @brief      Flushes the pending updates and applies them to this
  ///             accessibility bridge. Calling this with no pending updates
  ///             does nothing, and callers should call this method at the end
  ///             of an atomic batch to avoid leaving the tree in a unstable
  ///             state. For example if a node reparents from A to B, callers
  ///             should only call this method when both removal from A and
  ///             addition to B are in the pending updates.
  void CommitUpdates();
 
  //------------------------------------------------------------------------------
  /// @brief      Get the flutter platform node delegate with the given id from
  ///             this accessibility bridge. Returns expired weak_ptr if the
  ///             delegate associated with the id does not exist or has been
  ///             removed from the accessibility tree.
  ///
  /// @param[in]  id           The id of the flutter accessibility node you want
  ///                          to retrieve.
  std::weak_ptr<FlutterPlatformNodeDelegate>
  GetFlutterPlatformNodeDelegateFromID(AccessibilityNodeId id) const;
 
  //------------------------------------------------------------------------------
  /// @brief      Get the ax tree data from this accessibility bridge. The tree
  ///             data contains information such as the id of the node that
  ///             has the keyboard focus or the text selection range.
  const ui::AXTreeData& GetAXTreeData() const;
 
  //------------------------------------------------------------------------------
  /// @brief      Gets all pending accessibility events generated during
  ///             semantics updates. This is useful when deciding how to handle
  ///             events in AccessibilityBridgeDelegate::OnAccessibilityEvent in
  ///             case one may decide to handle an event differently based on
  ///             all pending events.
  const std::vector<ui::AXEventGenerator::TargetedEvent> GetPendingEvents()
      const;
 
  // |AXTreeManager|
  ui::AXNode* GetNodeFromTree(const ui::AXTreeID tree_id,
                              const ui::AXNode::AXID node_id) const override;
 
  // |AXTreeManager|
  ui::AXNode* GetNodeFromTree(const ui::AXNode::AXID node_id) const override;
 
  // |AXTreeManager|
  ui::AXTreeID GetTreeID() const override;
 
  // |AXTreeManager|
  ui::AXTreeID GetParentTreeID() const override;
 
  // |AXTreeManager|
  ui::AXNode* GetRootAsAXNode() const override;
 
  // |AXTreeManager|
  ui::AXNode* GetParentNodeFromParentTreeAsAXNode() const override;
 
  // |AXTreeManager|
  ui::AXTree* GetTree() const override;
 
  // |AXPlatformTreeManager|
  ui::AXPlatformNode* GetPlatformNodeFromTree(
      const ui::AXNode::AXID node_id) const override;
 
  // |AXPlatformTreeManager|
  ui::AXPlatformNode* GetPlatformNodeFromTree(
      const ui::AXNode& node) const override;
 
  // |AXPlatformTreeManager|
  ui::AXPlatformNodeDelegate* RootDelegate() const override;
 
 protected:
  //---------------------------------------------------------------------------
  /// @brief      Handle accessibility events generated due to accessibility
  ///             tree changes. These events are needed to be sent to native
  ///             accessibility system.  See ui::AXEventGenerator::Event for
  ///             possible events.
  ///
  /// @param[in]  targeted_event      The object that contains both the
  ///                                 generated event and the event target.
  virtual void OnAccessibilityEvent(
      ui::AXEventGenerator::TargetedEvent targeted_event) = 0;
 
  //---------------------------------------------------------------------------
  /// @brief      Creates a platform specific FlutterPlatformNodeDelegate.
  ///             Ownership passes to the caller. This method will be called
  ///             whenever a new AXNode is created in AXTree. Each platform
  ///             needs to implement this method in order to inject its
  ///             subclass into the accessibility bridge.
  virtual std::shared_ptr<FlutterPlatformNodeDelegate>
  CreateFlutterPlatformNodeDelegate() = 0;
 
 private:
  // See FlutterSemanticsNode in embedder.h
  typedef struct {
    int32_t id;
    FlutterSemanticsFlags* flags;
    FlutterSemanticsAction actions;
    int32_t text_selection_base;
    int32_t text_selection_extent;
    int32_t scroll_child_count;
    int32_t scroll_index;
    double scroll_position;
    double scroll_extent_max;
    double scroll_extent_min;
    std::string label;
    std::string hint;
    std::string value;
    std::string increased_value;
    std::string decreased_value;
    std::string tooltip;
    FlutterTextDirection text_direction;
    FlutterRect rect;
    FlutterTransformation transform;
    std::vector<int32_t> children_in_traversal_order;
    std::vector<int32_t> custom_accessibility_actions;
    int32_t heading_level;
  } SemanticsNode;
 
  // See FlutterSemanticsCustomAction in embedder.h
  typedef struct {
    int32_t id;
    FlutterSemanticsAction override_action;
    std::string label;
    std::string hint;
  } SemanticsCustomAction;
 
  std::unordered_map<AccessibilityNodeId,
                     std::shared_ptr<FlutterPlatformNodeDelegate>>
      id_wrapper_map_;
  std::unique_ptr<ui::AXTree> tree_;
  ui::AXEventGenerator event_generator_;
  std::unordered_map<int32_t, SemanticsNode> pending_semantics_node_updates_;
  std::unordered_map<int32_t, SemanticsCustomAction>
      pending_semantics_custom_action_updates_;
  AccessibilityNodeId last_focused_id_ = ui::AXNode::kInvalidAXID;
 
  void InitAXTree(const ui::AXTreeUpdate& initial_state);
 
  // Create an update that removes any nodes that will be reparented by
  // pending_semantics_updates_. Returns std::nullopt if none are reparented.
  std::optional<ui::AXTreeUpdate> CreateRemoveReparentedNodesUpdate();
 
  void GetSubTreeList(const SemanticsNode& target,
                      std::vector<SemanticsNode>& result);
  void ConvertFlutterUpdate(const SemanticsNode& node,
                            ui::AXTreeUpdate& tree_update);
  void SetRoleFromFlutterUpdate(ui::AXNodeData& node_data,
                                const SemanticsNode& node);
  void SetStateFromFlutterUpdate(ui::AXNodeData& node_data,
                                 const SemanticsNode& node);
  void SetActionsFromFlutterUpdate(ui::AXNodeData& node_data,
                                   const SemanticsNode& node);
  void SetBooleanAttributesFromFlutterUpdate(ui::AXNodeData& node_data,
                                             const SemanticsNode& node);
  void SetIntAttributesFromFlutterUpdate(ui::AXNodeData& node_data,
                                         const SemanticsNode& node);
  void SetIntListAttributesFromFlutterUpdate(ui::AXNodeData& node_data,
                                             const SemanticsNode& node);
  void SetStringListAttributesFromFlutterUpdate(ui::AXNodeData& node_data,
                                                const SemanticsNode& node);
  void SetNameFromFlutterUpdate(ui::AXNodeData& node_data,
                                const SemanticsNode& node);
  void SetValueFromFlutterUpdate(ui::AXNodeData& node_data,
                                 const SemanticsNode& node);
  void SetTooltipFromFlutterUpdate(ui::AXNodeData& node_data,
                                   const SemanticsNode& node);
  void SetTreeData(const SemanticsNode& node, ui::AXTreeUpdate& tree_update);
  SemanticsNode FromFlutterSemanticsNode(
      const FlutterSemanticsNode2& flutter_node);
  SemanticsCustomAction FromFlutterSemanticsCustomAction(
      const FlutterSemanticsCustomAction2& flutter_custom_action);
 
  // |AXTreeObserver|
  void OnNodeWillBeDeleted(ui::AXTree* tree, ui::AXNode* node) override;
 
  // |AXTreeObserver|
  void OnSubtreeWillBeDeleted(ui::AXTree* tree, ui::AXNode* node) override;
 
  // |AXTreeObserver|
  void OnNodeCreated(ui::AXTree* tree, ui::AXNode* node) override;
 
  // |AXTreeObserver|
  void OnNodeDeleted(ui::AXTree* tree, AccessibilityNodeId node_id) override;
 
  // |AXTreeObserver|
  void OnNodeReparented(ui::AXTree* tree, ui::AXNode* node) override;
 
  // |AXTreeObserver|
  void OnRoleChanged(ui::AXTree* tree,
                     ui::AXNode* node,
                     ax::mojom::Role old_role,
                     ax::mojom::Role new_role) override;
 
  // |AXTreeObserver|
  void OnNodeDataChanged(ui::AXTree* tree,
                         const ui::AXNodeData& old_node_data,
                         const ui::AXNodeData& new_node_data) override;
 
  // |AXTreeObserver|
  void OnAtomicUpdateFinished(
      ui::AXTree* tree,
      bool root_changed,
      const std::vector<ui::AXTreeObserver::Change>& changes) override;
 
  // |FlutterPlatformNodeDelegate::OwnerBridge|
  void SetLastFocusedId(AccessibilityNodeId node_id) override;
 
  // |FlutterPlatformNodeDelegate::OwnerBridge|
  AccessibilityNodeId GetLastFocusedId() override;
 
  // |FlutterPlatformNodeDelegate::OwnerBridge|
  gfx::NativeViewAccessible GetNativeAccessibleFromId(
      AccessibilityNodeId id) override;
 
  // |FlutterPlatformNodeDelegate::OwnerBridge|
  gfx::RectF RelativeToGlobalBounds(const ui::AXNode* node,
                                    bool& offscreen,
                                    bool clip_bounds) override;
 
  BASE_DISALLOW_COPY_AND_ASSIGN(AccessibilityBridge);
};
 
}  // namespace flutter
 
#endif  // FLUTTER_SHELL_PLATFORM_COMMON_ACCESSIBILITY_BRIDGE_H_