ui/accessibility/ax_tree.h

   1 // Copyright 2013 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef UI_ACCESSIBILITY_AX_TREE_H_
   6 #define UI_ACCESSIBILITY_AX_TREE_H_
   7
   8 #include <set>
   9
  10 #include "base/containers/hash_tables.h"
  11 #include "ui/accessibility/ax_export.h"
  12 #include "ui/accessibility/ax_tree_update.h"
  13
  14 namespace ui {
  15
  16 class AXNode;
  17 struct AXTreeUpdateState;
  18
  19 // Used when you want to be notified when changes happen to the tree.
  20 //
  21 // Some of the notifications are called in the middle of an update operation.
  22 // Be careful, as the tree may be in an inconsistent state at this time;
  23 // don't walk the parents and children at this time:
  24 //   OnNodeWillBeDeleted
  25 //   OnSubtreeWillBeDeleted
  26 //   OnNodeCreated
  27 //   OnNodeChanged
  28 //
  29 // In addition, one additional notification is fired at the end of an
  30 // atomic update, and it provides a vector of nodes that were added or
  31 // changed, for final postprocessing:
  32 //   OnAtomicUpdateFinished
  33 //
  34 class AX_EXPORT AXTreeDelegate {
  35  public:
  36   AXTreeDelegate();
  37   virtual ~AXTreeDelegate();
  38
  39   // Called just before a node is deleted. Its id and data will be valid,
  40   // but its links to parents and children are invalid. This is called
  41   // in the middle of an update, the tree may be in an invalid state!
  42   virtual void OnNodeWillBeDeleted(AXNode* node) = 0;
  43
  44   // Same as OnNodeWillBeDeleted, but only called once for an entire subtree.
  45   // This is called in the middle of an update, the tree may be in an
  46   // invalid state!
  47   virtual void OnSubtreeWillBeDeleted(AXNode* node) = 0;
  48
  49   // Called immediately after a new node is created. The tree may be in
  50   // the middle of an update, don't walk the parents and children now.
  51   virtual void OnNodeCreated(AXNode* node) = 0;
  52
  53   // Called when a node changes its data or children. The tree may be in
  54   // the middle of an update, don't walk the parents and children now.
  55   virtual void OnNodeChanged(AXNode* node) = 0;
  56
  57   enum ChangeType {
  58     NODE_CREATED,
  59     SUBTREE_CREATED,
  60     NODE_CHANGED
  61   };
  62
  63   struct Change {
  64     Change(AXNode* node, ChangeType type) {
  65       this->node = node;
  66       this->type = type;
  67     }
  68     AXNode* node;
  69     ChangeType type;
  70   };
  71
  72   // Called at the end of the update operation. Every node that was added
  73   // or changed will be included in |changes|, along with an enum indicating
  74   // the type of change - either (1) a node was created, (2) a node was created
  75   // and it's the root of a new subtree, or (3) a node was changed. Finally,
  76   // a bool indicates if the root of the tree was changed or not.
  77   virtual void OnAtomicUpdateFinished(bool root_changed,
  78                                       const std::vector<Change>& changes) = 0;
  79 };
  80
  81 // AXTree is a live, managed tree of AXNode objects that can receive
  82 // updates from another AXTreeSource via AXTreeUpdates, and it can be
  83 // used as a source for sending updates to another client tree.
  84 // It's designed to be subclassed to implement support for native
  85 // accessibility APIs on a specific platform.
  86 class AX_EXPORT AXTree {
  87  public:
  88   AXTree();
  89   explicit AXTree(const AXTreeUpdate& initial_state);
  90   virtual ~AXTree();
  91
  92   virtual void SetDelegate(AXTreeDelegate* delegate);
  93
  94   AXNode* root() const { return root_; }
  95
  96   // Returns the AXNode with the given |id| if it is part of this AXTree.
  97   AXNode* GetFromId(int32 id) const;
  98
  99   // Returns true on success. If it returns false, it's a fatal error
 100   // and this tree should be destroyed, and the source of the tree update
 101   // should not be trusted any longer.
 102   virtual bool Unserialize(const AXTreeUpdate& update);
 103
 104   // Return a multi-line indented string representation, for logging.
 105   std::string ToString() const;
 106
 107   // A string describing the error from an unsuccessful Unserialize,
 108   // for testing and debugging.
 109   const std::string& error() const { return error_; }
 110
 111  private:
 112   AXNode* CreateNode(AXNode* parent, int32 id, int32 index_in_parent);
 113
 114   // This is called from within Unserialize(), it returns true on success.
 115   bool UpdateNode(const AXNodeData& src, AXTreeUpdateState* update_state);
 116
 117   void OnRootChanged();
 118
 119   // Notify the delegate that the subtree rooted at |node| will be destroyed,
 120   // then call DestroyNodeAndSubtree on it.
 121   void DestroySubtree(AXNode* node);
 122
 123   // Call Destroy() on |node|, and delete it from the id map, and then
 124   // call recursively on all nodes in its subtree.
 125   void DestroyNodeAndSubtree(AXNode* node);
 126
 127   // Iterate over the children of |node| and for each child, destroy the
 128   // child and its subtree if its id is not in |new_child_ids|. Returns
 129   // true on success, false on fatal error.
 130   bool DeleteOldChildren(AXNode* node,
 131                          const std::vector<int32>& new_child_ids);
 132
 133   // Iterate over |new_child_ids| and populate |new_children| with
 134   // pointers to child nodes, reusing existing nodes already in the tree
 135   // if they exist, and creating otherwise. Reparenting is disallowed, so
 136   // if the id already exists as the child of another node, that's an
 137   // error. Returns true on success, false on fatal error.
 138   bool CreateNewChildVector(AXNode* node,
 139                             const std::vector<int32>& new_child_ids,
 140                             std::vector<AXNode*>* new_children,
 141                             AXTreeUpdateState* update_state);
 142
 143   AXTreeDelegate* delegate_;
 144   AXNode* root_;
 145   base::hash_map<int32, AXNode*> id_map_;
 146   std::string error_;
 147 };
 148
 149 }  // namespace ui
 150
 151 #endif  // UI_ACCESSIBILITY_AX_TREE_H_