ui/accessibility/ax_tree_update.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_UPDATE_H_
   6 #define UI_ACCESSIBILITY_AX_TREE_UPDATE_H_
   7
   8 #include <string>
   9 #include <vector>
  10
  11 #include "base/strings/string_number_conversions.h"
  12 #include "ui/accessibility/ax_node_data.h"
  13
  14 namespace ui {
  15
  16 // An AXTreeUpdate is a serialized representation of an atomic change
  17 // to an AXTree. The sender and receiver must be in sync; the update
  18 // is only meant to bring the tree from a specific previous state into
  19 // its next state. Trying to apply it to the wrong tree should immediately
  20 // die with a fatal assertion.
  21 //
  22 // An AXTreeUpdate consists of an optional node id to clear (meaning
  23 // that all of that node's children and their descendants are deleted),
  24 // followed by an ordered vector of AXNodeData structures to be applied
  25 // to the tree in order.
  26 //
  27 // Suppose that the next AXNodeData to be applied is |node|. The following
  28 // invariants must hold:
  29 // 1. Either |node.id| is already in the tree, or else the tree is empty,
  30 //        |node| is the new root of the tree, and
  31 //        |node.role| == WebAXRoleRootWebArea.
  32 // 2. Every child id in |node.child_ids| must either be already a child
  33 //        of this node, or a new id not previously in the tree. It is not
  34 //        allowed to "reparent" a child to this node without first removing
  35 //        that child from its previous parent.
  36 // 3. When a new id appears in |node.child_ids|, the tree should create a
  37 //        new uninitialized placeholder node for it immediately. That
  38 //        placeholder must be updated within the same AXTreeUpdate, otherwise
  39 //        it's a fatal error. This guarantees the tree is always complete
  40 //        before or after an AXTreeUpdate.
  41 template<typename AXNodeData> struct AXTreeUpdate {
  42   AXTreeUpdate();
  43   ~AXTreeUpdate();
  44
  45   // The id of a node to clear, before applying any updates,
  46   // or 0 if no nodes should be cleared. Clearing a node means deleting
  47   // all of its children and their descendants, but leaving that node in
  48   // the tree. It's an error to clear a node but not subsequently update it
  49   // as part of the tree update.
  50   int node_id_to_clear;
  51
  52   // A vector of nodes to update, according to the rules above.
  53   std::vector<AXNodeData> nodes;
  54
  55   // Return a multi-line indented string representation, for logging.
  56   std::string ToString() const;
  57
  58   // TODO(dmazzoni): location changes
  59 };
  60
  61 template<typename AXNodeData>
  62 AXTreeUpdate<AXNodeData>::AXTreeUpdate() : node_id_to_clear(0) {
  63 }
  64
  65 template<typename AXNodeData>
  66 AXTreeUpdate<AXNodeData>::~AXTreeUpdate() {
  67 }
  68
  69 template<typename AXNodeData>
  70 std::string AXTreeUpdate<AXNodeData>::ToString() const {
  71   std::string result;
  72   if (node_id_to_clear != 0) {
  73     result += "AXTreeUpdate: clear node " +
  74         base::IntToString(node_id_to_clear) + "\n";
  75   }
  76
  77   // The challenge here is that we want to indent the nodes being updated
  78   // so that parent/child relationships are clear, but we don't have access
  79   // to the rest of the tree for context, so we have to try to show the
  80   // relative indentation of child nodes in this update relative to their
  81   // parents.
  82   base::hash_map<int32, int> id_to_indentation;
  83   for (size_t i = 0; i < nodes.size(); ++i) {
  84     int indent = id_to_indentation[nodes[i].id];
  85     result += std::string(2 * indent, ' ');
  86     result += nodes[i].ToString() + "\n";
  87     for (size_t j = 0; j < nodes[i].child_ids.size(); ++j)
  88       id_to_indentation[nodes[i].child_ids[j]] = indent + 1;
  89   }
  90
  91   return result;
  92 }
  93
  94 }  // namespace ui
  95
  96 #endif  // UI_ACCESSIBILITY_AX_TREE_UPDATE_H_