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 <vector>
   9
  10 #include "ui/accessibility/ax_node_data.h"
  11
  12 namespace ui {
  13
  14 // An AXTreeUpdate is a serialized representation of an atomic change
  15 // to an AXTree. The sender and receiver must be in sync; the update
  16 // is only meant to bring the tree from a specific previous state into
  17 // its next state. Trying to apply it to the wrong tree should immediately
  18 // die with a fatal assertion.
  19 //
  20 // An AXTreeUpdate consists of an optional node id to clear (meaning
  21 // that all of that node's children and their descendants are deleted),
  22 // followed by an ordered vector of AXNodeData structures to be applied
  23 // to the tree in order.
  24 //
  25 // Suppose that the next AXNodeData to be applied is |node|. The following
  26 // invariants must hold:
  27 // 1. Either |node.id| is already in the tree, or else the tree is empty,
  28 //        |node| is the new root of the tree, and
  29 //        |node.role| == WebAXRoleRootWebArea.
  30 // 2. Every child id in |node.child_ids| must either be already a child
  31 //        of this node, or a new id not previously in the tree. It is not
  32 //        allowed to "reparent" a child to this node without first removing
  33 //        that child from its previous parent.
  34 // 3. When a new id appears in |node.child_ids|, the tree should create a
  35 //        new uninitialized placeholder node for it immediately. That
  36 //        placeholder must be updated within the same AXTreeUpdate, otherwise
  37 //        it's a fatal error. This guarantees the tree is always complete
  38 //        before or after an AXTreeUpdate.
  39 struct AX_EXPORT AXTreeUpdate {
  40   AXTreeUpdate();
  41   ~AXTreeUpdate();
  42
  43   // The id of a node to clear, before applying any updates,
  44   // or 0 if no nodes should be cleared. Clearing a node means deleting
  45   // all of its children and their descendants, but leaving that node in
  46   // the tree. It's an error to clear a node but not subsequently update it
  47   // as part of the tree update.
  48   int node_id_to_clear;
  49
  50   // A vector of nodes to update, according to the rules above.
  51   std::vector<AXNodeData> nodes;
  52
  53   // TODO(dmazzoni): location changes
  54 };
  55
  56 }  // namespace ui
  57
  58 #endif  // UI_ACCESSIBILITY_AX_TREE_UPDATE_H_