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 }  // 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::GetFromId(int32 id) const {
  71   base::hash_map<int32, AXNode*>::const_iterator iter = id_map_.find(id);
  72   return iter != id_map_.end() ? iter->second : NULL;
  73 }
  74
  75 bool AXTree::Unserialize(const AXTreeUpdate& update) {
  76   AXTreeUpdateState update_state;
  77   int32 old_root_id = root_ ? root_->id() : 0;
  78
  79   if (update.node_id_to_clear != 0) {
  80     AXNode* node = GetFromId(update.node_id_to_clear);
  81     if (!node) {
  82       error_ = base::StringPrintf("Bad node_id_to_clear: %d",
  83                                   update.node_id_to_clear);
  84       return false;
  85     }
  86     if (node == root_) {
  87       DestroySubtree(root_);
  88       root_ = NULL;
  89     } else {
  90       for (int i = 0; i < node->child_count(); ++i)
  91         DestroySubtree(node->ChildAtIndex(i));
  92       std::vector<AXNode*> children;
  93       node->SwapChildren(children);
  94       update_state.pending_nodes.insert(node);
  95     }
  96   }
  97
  98   for (size_t i = 0; i < update.nodes.size(); ++i) {
  99     if (!UpdateNode(update.nodes[i], &update_state))
 100       return false;
 101   }
 102
 103   if (!update_state.pending_nodes.empty()) {
 104     error_ = "Nodes left pending by the update:";
 105     for (std::set<AXNode*>::iterator iter = update_state.pending_nodes.begin();
 106          iter != update_state.pending_nodes.end(); ++iter) {
 107       error_ += base::StringPrintf(" %d", (*iter)->id());
 108     }
 109     return false;
 110   }
 111
 112   if (delegate_) {
 113     std::set<AXNode*>& new_nodes = update_state.new_nodes;
 114     std::vector<AXTreeDelegate::Change> changes;
 115     changes.reserve(update.nodes.size());
 116     for (size_t i = 0; i < update.nodes.size(); ++i) {
 117       AXNode* node = GetFromId(update.nodes[i].id);
 118       if (new_nodes.find(node) != new_nodes.end()) {
 119         if (new_nodes.find(node->parent()) == new_nodes.end()) {
 120           changes.push_back(
 121               AXTreeDelegate::Change(node, AXTreeDelegate::SUBTREE_CREATED));
 122         } else {
 123           changes.push_back(
 124               AXTreeDelegate::Change(node, AXTreeDelegate::NODE_CREATED));
 125         }
 126       } else {
 127         changes.push_back(
 128             AXTreeDelegate::Change(node, AXTreeDelegate::NODE_CHANGED));
 129       }
 130     }
 131     delegate_->OnAtomicUpdateFinished(root_->id() != old_root_id, changes);
 132   }
 133
 134   return true;
 135 }
 136
 137 std::string AXTree::ToString() const {
 138   return TreeToStringHelper(root_, 0);
 139 }
 140
 141 AXNode* AXTree::CreateNode(AXNode* parent, int32 id, int32 index_in_parent) {
 142   AXNode* new_node = new AXNode(parent, id, index_in_parent);
 143   id_map_[new_node->id()] = new_node;
 144   if (delegate_)
 145     delegate_->OnNodeCreated(new_node);
 146   return new_node;
 147 }
 148
 149 bool AXTree::UpdateNode(const AXNodeData& src,
 150                         AXTreeUpdateState* update_state) {
 151   // This method updates one node in the tree based on serialized data
 152   // received in an AXTreeUpdate. See AXTreeUpdate for pre and post
 153   // conditions.
 154
 155   // Look up the node by id. If it's not found, then either the root
 156   // of the tree is being swapped, or we're out of sync with the source
 157   // and this is a serious error.
 158   AXNode* node = GetFromId(src.id);
 159   AXNode* new_root = NULL;
 160   if (node) {
 161     update_state->pending_nodes.erase(node);
 162     node->SetData(src);
 163   } else {
 164     if (src.role != AX_ROLE_ROOT_WEB_AREA) {
 165       error_ = base::StringPrintf(
 166           "%d is not in the tree and not the new root", src.id);
 167       return false;
 168     }
 169     new_root = CreateNode(NULL, src.id, 0);
 170     node = new_root;
 171     update_state->new_nodes.insert(node);
 172     node->SetData(src);
 173   }
 174
 175   if (delegate_)
 176     delegate_->OnNodeChanged(node);
 177
 178   // First, delete nodes that used to be children of this node but aren't
 179   // anymore.
 180   if (!DeleteOldChildren(node, src.child_ids)) {
 181     if (new_root)
 182       DestroySubtree(new_root);
 183     return false;
 184   }
 185
 186   // Now build a new children vector, reusing nodes when possible,
 187   // and swap it in.
 188   std::vector<AXNode*> new_children;
 189   bool success = CreateNewChildVector(
 190       node, src.child_ids, &new_children, update_state);
 191   node->SwapChildren(new_children);
 192
 193   // Update the root of the tree if needed.
 194   if (src.role == AX_ROLE_ROOT_WEB_AREA &&
 195       (!root_ || root_->id() != src.id)) {
 196     if (root_)
 197       DestroySubtree(root_);
 198     root_ = node;
 199   }
 200
 201   return success;
 202 }
 203
 204 void AXTree::DestroySubtree(AXNode* node) {
 205   if (delegate_)
 206     delegate_->OnSubtreeWillBeDeleted(node);
 207   DestroyNodeAndSubtree(node);
 208 }
 209
 210 void AXTree::DestroyNodeAndSubtree(AXNode* node) {
 211   id_map_.erase(node->id());
 212   for (int i = 0; i < node->child_count(); ++i)
 213     DestroyNodeAndSubtree(node->ChildAtIndex(i));
 214   if (delegate_)
 215     delegate_->OnNodeWillBeDeleted(node);
 216   node->Destroy();
 217 }
 218
 219 bool AXTree::DeleteOldChildren(AXNode* node,
 220                                const std::vector<int32>& new_child_ids) {
 221   // Create a set of child ids in |src| for fast lookup, and return false
 222   // if a duplicate is found;
 223   std::set<int32> new_child_id_set;
 224   for (size_t i = 0; i < new_child_ids.size(); ++i) {
 225     if (new_child_id_set.find(new_child_ids[i]) != new_child_id_set.end()) {
 226       error_ = base::StringPrintf("Node %d has duplicate child id %d",
 227                                   node->id(), new_child_ids[i]);
 228       return false;
 229     }
 230     new_child_id_set.insert(new_child_ids[i]);
 231   }
 232
 233   // Delete the old children.
 234   const std::vector<AXNode*>& old_children = node->children();
 235   for (size_t i = 0; i < old_children.size(); ++i) {
 236     int old_id = old_children[i]->id();
 237     if (new_child_id_set.find(old_id) == new_child_id_set.end())
 238       DestroySubtree(old_children[i]);
 239   }
 240
 241   return true;
 242 }
 243
 244 bool AXTree::CreateNewChildVector(AXNode* node,
 245                                   const std::vector<int32>& new_child_ids,
 246                                   std::vector<AXNode*>* new_children,
 247                                   AXTreeUpdateState* update_state) {
 248   bool success = true;
 249   for (size_t i = 0; i < new_child_ids.size(); ++i) {
 250     int32 child_id = new_child_ids[i];
 251     int32 index_in_parent = static_cast<int32>(i);
 252     AXNode* child = GetFromId(child_id);
 253     if (child) {
 254       if (child->parent() != node) {
 255         // This is a serious error - nodes should never be reparented.
 256         // If this case occurs, continue so this node isn't left in an
 257         // inconsistent state, but return failure at the end.
 258         error_ = base::StringPrintf(
 259             "Node %d reparented from %d to %d",
 260             child->id(),
 261             child->parent() ? child->parent()->id() : 0,
 262             node->id());
 263         success = false;
 264         continue;
 265       }
 266       child->SetIndexInParent(index_in_parent);
 267     } else {
 268       child = CreateNode(node, child_id, index_in_parent);
 269       update_state->pending_nodes.insert(child);
 270       update_state->new_nodes.insert(child);
 271     }
 272     new_children->push_back(child);
 273   }
 274
 275   return success;
 276 }
 277
 278 }  // namespace ui