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// Copyright 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef UI_ACCESSIBILITY_AX_TREE_UPDATE_H_
#define UI_ACCESSIBILITY_AX_TREE_UPDATE_H_
#include <stddef.h>
#include <stdint.h>
#include <string>
#include <vector>
#include "base/containers/hash_tables.h"
#include "base/strings/string_number_conversions.h"
#include "ui/accessibility/ax_node_data.h"
#include "ui/accessibility/ax_tree_data.h"
namespace ui {
// An AXTreeUpdate is a serialized representation of an atomic change
// to an AXTree. The sender and receiver must be in sync; the update
// is only meant to bring the tree from a specific previous state into
// its next state. Trying to apply it to the wrong tree should immediately
// die with a fatal assertion.
//
// An AXTreeUpdate consists of an optional node id to clear (meaning
// that all of that node's children and their descendants are deleted),
// followed by an ordered vector of zero or more AXNodeData structures to
// be applied to the tree in order. An update may also include an optional
// update to the AXTreeData structure that applies to the tree as a whole.
//
// Suppose that the next AXNodeData to be applied is |node|. The following
// invariants must hold:
// 1. Either |node.id| is already in the tree, or else the tree is empty,
// |node| is the new root of the tree, and
// |node.role| == WebAXRoleRootWebArea.
// 2. Every child id in |node.child_ids| must either be already a child
// of this node, or a new id not previously in the tree. It is not
// allowed to "reparent" a child to this node without first removing
// that child from its previous parent.
// 3. When a new id appears in |node.child_ids|, the tree should create a
// new uninitialized placeholder node for it immediately. That
// placeholder must be updated within the same AXTreeUpdate, otherwise
// it's a fatal error. This guarantees the tree is always complete
// before or after an AXTreeUpdate.
template<typename AXNodeData, typename AXTreeData> struct AXTreeUpdateBase {
AXTreeUpdateBase() = default;
~AXTreeUpdateBase() = default;
// If |has_tree_data| is true, the value of |tree_data| should be used
// to update the tree data, otherwise it should be ignored.
bool has_tree_data = false;
AXTreeData tree_data;
// The id of a node to clear, before applying any updates,
// or 0 if no nodes should be cleared. Clearing a node means deleting
// all of its children and their descendants, but leaving that node in
// the tree. It's an error to clear a node but not subsequently update it
// as part of the tree update.
int node_id_to_clear = 0;
// The id of the root of the tree, if the root is changing. This is
// required to be set if the root of the tree is changing or Unserialize
// will fail. If the root of the tree is not changing this is optional
// and it is allowed to pass 0.
int root_id = 0;
// A vector of nodes to update, according to the rules above.
std::vector<AXNodeData> nodes;
// Return a multi-line indented string representation, for logging.
std::string ToString() const;
// TODO(dmazzoni): location changes
};
using AXTreeUpdate = AXTreeUpdateBase<AXNodeData, AXTreeData>;
template<typename AXNodeData, typename AXTreeData>
std::string AXTreeUpdateBase<AXNodeData, AXTreeData>::ToString() const {
std::string result;
if (has_tree_data) {
result += "AXTreeUpdate tree data:" + tree_data.ToString() + "\n";
}
if (node_id_to_clear != 0) {
result += "AXTreeUpdate: clear node " +
base::IntToString(node_id_to_clear) + "\n";
}
if (root_id != 0) {
result += "AXTreeUpdate: root id " +
base::IntToString(root_id) + "\n";
}
// The challenge here is that we want to indent the nodes being updated
// so that parent/child relationships are clear, but we don't have access
// to the rest of the tree for context, so we have to try to show the
// relative indentation of child nodes in this update relative to their
// parents.
base::hash_map<int32_t, int> id_to_indentation;
for (size_t i = 0; i < nodes.size(); ++i) {
int indent = id_to_indentation[nodes[i].id];
result += std::string(2 * indent, ' ');
result += nodes[i].ToString() + "\n";
for (size_t j = 0; j < nodes[i].child_ids.size(); ++j)
id_to_indentation[nodes[i].child_ids[j]] = indent + 1;
}
return result;
}
} // namespace ui
#endif // UI_ACCESSIBILITY_AX_TREE_UPDATE_H_
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