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 "ui/accessibility/ax_node_data.h"
  12
  13 namespace ui {
  14
  15 // An AXTreeUpdate is a serialized representation of an atomic change
  16 // to an AXTree. The sender and receiver must be in sync; the update
  17 // is only meant to bring the tree from a specific previous state into
  18 // its next state. Trying to apply it to the wrong tree should immediately
  19 // die with a fatal assertion.
  20 //
  21 // An AXTreeUpdate consists of an optional node id to clear (meaning
  22 // that all of that node's children and their descendants are deleted),
  23 // followed by an ordered vector of AXNodeData structures to be applied
  24 // to the tree in order.
  25 //
  26 // Suppose that the next AXNodeData to be applied is |node|. The following
  27 // invariants must hold:
  28 // 1. Either |node.id| is already in the tree, or else the tree is empty,
  29 //        |node| is the new root of the tree, and
  30 //        |node.role| == WebAXRoleRootWebArea.
  31 // 2. Every child id in |node.child_ids| must either be already a child
  32 //        of this node, or a new id not previously in the tree. It is not
  33 //        allowed to "reparent" a child to this node without first removing
  34 //        that child from its previous parent.
  35 // 3. When a new id appears in |node.child_ids|, the tree should create a
  36 //        new uninitialized placeholder node for it immediately. That
  37 //        placeholder must be updated within the same AXTreeUpdate, otherwise
  38 //        it's a fatal error. This guarantees the tree is always complete
  39 //        before or after an AXTreeUpdate.
  40 struct AX_EXPORT AXTreeUpdate {
  41   AXTreeUpdate();
  42   ~AXTreeUpdate();
  43
  44   // The id of a node to clear, before applying any updates,
  45   // or 0 if no nodes should be cleared. Clearing a node means deleting
  46   // all of its children and their descendants, but leaving that node in
  47   // the tree. It's an error to clear a node but not subsequently update it
  48   // as part of the tree update.
  49   int node_id_to_clear;
  50
  51   // A vector of nodes to update, according to the rules above.
  52   std::vector<AXNodeData> nodes;
  53
  54   // Return a multi-line indented string representation, for logging.
  55   std::string ToString() const;
  56
  57   // TODO(dmazzoni): location changes
  58 };
  59
  60 }  // namespace ui
  61
  62 #endif  // UI_ACCESSIBILITY_AX_TREE_UPDATE_H_