ui/accessibility/ax_tree.cc

   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 #include "ui/accessibility/ax_tree.h"
   6
   7 #include <set>
   8
   9 #include "base/logging.h"
  10 #include "base/strings/stringprintf.h"
  11 #include "ui/accessibility/ax_node.h"
  12
  13 namespace ui {
  14
  15 namespace {
  16
  17 std::string TreeToStringHelper(AXNode* node, int indent) {
  18   std::string result = std::string(2 * indent, ' ');
  19   result += node->data().ToString() + "\n";
  20   for (int i = 0; i < node->child_count(); ++i)
  21     result += TreeToStringHelper(node->ChildAtIndex(i), indent + 1);
  22   return result;
  23 }
  24
  25 }  // anonymous namespace
  26
  27 // Intermediate state to keep track of during a tree update.
  28 struct AXTreeUpdateState {
  29   // During an update, this keeps track of all nodes that have been
  30   // implicitly referenced as part of this update, but haven't been
  31   // updated yet. It's an error if there are any pending nodes at the
  32   // end of Unserialize.
  33   std::set<AXNode*> pending_nodes;
  34
  35   // Keeps track of new nodes created during this update.
  36   std::set<AXNode*> new_nodes;
  37 };
  38
  39 AXTreeDelegate::AXTreeDelegate() {
  40 }
  41
  42 AXTreeDelegate::~AXTreeDelegate() {
  43 }
  44
  45 AXTree::AXTree()
  46     : delegate_(NULL), root_(NULL) {
  47   AXNodeData root;
  48   root.id = -1;
  49   root.role = AX_ROLE_ROOT_WEB_AREA;
  50
  51   AXTreeUpdate initial_state;
  52   initial_state.nodes.push_back(root);
  53   CHECK(Unserialize(initial_state)) << error();
  54 }
  55
  56 AXTree::AXTree(const AXTreeUpdate& initial_state)
  57     : delegate_(NULL), root_(NULL) {
  58   CHECK(Unserialize(initial_state)) << error();
  59 }
  60
  61 AXTree::~AXTree() {
  62   if (root_)
  63     DestroyNodeAndSubtree(root_);
  64 }
  65
  66 void AXTree::SetDelegate(AXTreeDelegate* delegate) {
  67   delegate_ = delegate;
  68 }
  69
  70 AXNode* AXTree::GetRoot() const {
  71   return root_;
  72 }
  73
  74 AXNode* AXTree::GetFromId(int32 id) const {
  75   base::hash_map<int32, AXNode*>::const_iterator iter = id_map_.find(id);
  76   return iter != id_map_.end() ? (iter->second) : NULL;
  77 }
  78
  79 bool AXTree::Unserialize(const AXTreeUpdate& update) {
  80   AXTreeUpdateState update_state;
  81   int32 old_root_id = root_ ? root_->id() : 0;
  82
  83   if (update.node_id_to_clear != 0) {
  84     AXNode* node = GetFromId(update.node_id_to_clear);
  85     if (!node) {
  86       error_ = base::StringPrintf("Bad node_id_to_clear: %d",
  87                                   update.node_id_to_clear);
  88       return false;
  89     }
  90     if (node == root_) {
  91       DestroyNodeAndSubtree(root_);
  92       root_ = NULL;
  93     } else {
  94       for (int i = 0; i < node->child_count(); ++i)
  95         DestroyNodeAndSubtree(node->ChildAtIndex(i));
  96       std::vector<AXNode*> children;
  97       node->SwapChildren(children);
  98       update_state.pending_nodes.insert(node);
  99     }
 100   }
 101
 102   for (size_t i = 0; i < update.nodes.size(); ++i) {
 103     if (!UpdateNode(update.nodes[i], &update_state))
 104       return false;
 105   }
 106
 107   if (!update_state.pending_nodes.empty()) {
 108     error_ = "Nodes left pending by the update:";
 109     for (std::set<AXNode*>::iterator iter = update_state.pending_nodes.begin();
 110          iter != update_state.pending_nodes.end(); ++iter) {
 111       error_ += base::StringPrintf(" %d", (*iter)->id());
 112     }
 113     return false;
 114   }
 115
 116   if (delegate_) {
 117     for (size_t i = 0; i < update.nodes.size(); ++i) {
 118       AXNode* node = GetFromId(update.nodes[i].id);
 119       if (update_state.new_nodes.find(node) != update_state.new_nodes.end()) {
 120         delegate_->OnNodeCreationFinished(node);
 121         update_state.new_nodes.erase(node);
 122       } else {
 123         delegate_->OnNodeChangeFinished(node);
 124       }
 125     }
 126     if (root_->id() != old_root_id)
 127       delegate_->OnRootChanged(root_);
 128   }
 129
 130   return true;
 131 }
 132
 133 std::string AXTree::ToString() const {
 134   return TreeToStringHelper(root_, 0);
 135 }
 136
 137 AXNode* AXTree::CreateNode(
 138     AXNode* parent, int32 id, int32 index_in_parent) {
 139   AXNode* new_node = new AXNode(parent, id, index_in_parent);
 140   id_map_[new_node->id()] = new_node;
 141   if (delegate_)
 142     delegate_->OnNodeCreated(new_node);
 143   return new_node;
 144 }
 145
 146 bool AXTree::UpdateNode(
 147     const AXNodeData& src, AXTreeUpdateState* update_state) {
 148   // This method updates one node in the tree based on serialized data
 149   // received in an AXTreeUpdate. See AXTreeUpdate for pre and post
 150   // conditions.
 151
 152   // Look up the node by id. If it's not found, then either the root
 153   // of the tree is being swapped, or we're out of sync with the source
 154   // and this is a serious error.
 155   AXNode* node = GetFromId(src.id);
 156   AXNode* new_node = NULL;
 157   if (node) {
 158     update_state->pending_nodes.erase(node);
 159     node->SetData(src);
 160     if (delegate_)
 161       delegate_->OnNodeChanged(node);
 162   } else {
 163     if (src.role != AX_ROLE_ROOT_WEB_AREA) {
 164       error_ = base::StringPrintf(
 165           "%d is not in the tree and not the new root", src.id);
 166       return false;
 167     }
 168     new_node = CreateNode(NULL, src.id, 0);
 169     node = new_node;
 170     update_state->new_nodes.insert(node);
 171     node->SetData(src);
 172   }
 173
 174   // First, delete nodes that used to be children of this node but aren't
 175   // anymore.
 176   if (!DeleteOldChildren(node, src.child_ids)) {
 177     if (new_node)
 178       DestroyNodeAndSubtree(new_node);
 179     return false;
 180   }
 181
 182   // Now build a new children vector, reusing nodes when possible,
 183   // and swap it in.
 184   std::vector<AXNode*> new_children;
 185   bool success = CreateNewChildVector(
 186       node, src.child_ids, &new_children, update_state);
 187   node->SwapChildren(new_children);
 188
 189   // Update the root of the tree if needed.
 190   if (src.role == AX_ROLE_ROOT_WEB_AREA &&
 191       (!root_ || root_->id() != src.id)) {
 192     if (root_)
 193       DestroyNodeAndSubtree(root_);
 194     root_ = node;
 195   }
 196
 197   return success;
 198 }
 199
 200 void AXTree::DestroyNodeAndSubtree(AXNode* node) {
 201   id_map_.erase(node->id());
 202   for (int i = 0; i < node->child_count(); ++i)
 203     DestroyNodeAndSubtree(node->ChildAtIndex(i));
 204   if (delegate_)
 205     delegate_->OnNodeWillBeDeleted(node);
 206   node->Destroy();
 207 }
 208
 209 bool AXTree::DeleteOldChildren(AXNode* node,
 210                                const std::vector<int32> new_child_ids) {
 211   // Create a set of child ids in |src| for fast lookup, and return false
 212   // if a duplicate is found;
 213   std::set<int32> new_child_id_set;
 214   for (size_t i = 0; i < new_child_ids.size(); ++i) {
 215     if (new_child_id_set.find(new_child_ids[i]) != new_child_id_set.end()) {
 216       error_ = base::StringPrintf("Node %d has duplicate child id %d",
 217                                   node->id(), new_child_ids[i]);
 218       return false;
 219     }
 220     new_child_id_set.insert(new_child_ids[i]);
 221   }
 222
 223   // Delete the old children.
 224   const std::vector<AXNode*>& old_children = node->children();
 225   for (size_t i = 0; i < old_children.size(); ++i) {
 226     int old_id = old_children[i]->id();
 227     if (new_child_id_set.find(old_id) == new_child_id_set.end())
 228       DestroyNodeAndSubtree(old_children[i]);
 229   }
 230
 231   return true;
 232 }
 233
 234 bool AXTree::CreateNewChildVector(AXNode* node,
 235                                   const std::vector<int32> new_child_ids,
 236                                   std::vector<AXNode*>* new_children,
 237                                   AXTreeUpdateState* update_state) {
 238   bool success = true;
 239   for (size_t i = 0; i < new_child_ids.size(); ++i) {
 240     int32 child_id = new_child_ids[i];
 241     int32 index_in_parent = static_cast<int32>(i);
 242     AXNode* child = GetFromId(child_id);
 243     if (child) {
 244       if (child->parent() != node) {
 245         // This is a serious error - nodes should never be reparented.
 246         // If this case occurs, continue so this node isn't left in an
 247         // inconsistent state, but return failure at the end.
 248         error_ = base::StringPrintf(
 249             "Node %d reparented from %d to %d",
 250             child->id(),
 251             child->parent() ? child->parent()->id() : 0,
 252             node->id());
 253         success = false;
 254         continue;
 255       }
 256       child->SetIndexInParent(index_in_parent);
 257     } else {
 258       child = CreateNode(node, child_id, index_in_parent);
 259       update_state->pending_nodes.insert(child);
 260       update_state->new_nodes.insert(child);
 261     }
 262     new_children->push_back(child);
 263   }
 264
 265   return success;
 266 }
 267
 268 }  // namespace ui