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// Copyright (c) 2011 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_BASE_MODELS_TREE_NODE_ITERATOR_H_
#define UI_BASE_MODELS_TREE_NODE_ITERATOR_H_
#include <stack>
#include "base/callback.h"
#include "base/logging.h"
#include "base/macros.h"
namespace ui {
// Iterator that iterates over the descendants of a node. The iteration does
// not include the node itself, only the descendants. The following illustrates
// typical usage:
// while (iterator.has_next()) {
// Node* node = iterator.Next();
// // do something with node.
// }
template <class NodeType>
class TreeNodeIterator {
public:
typedef base::Callback<bool(NodeType*)> PruneCallback;
// This contructor accepts an optional filter function |prune| which could be
// used to prune complete branches of the tree. The filter function will be
// evaluated on each tree node and if it evaluates to true the node and all
// its descendants will be skipped by the iterator.
TreeNodeIterator(NodeType* node, const PruneCallback& prune)
: prune_(prune) {
int index = 0;
// Move forward through the children list until the first non prunable node.
// This is to satisfy the iterator invariant that the current index in the
// Position at the top of the _positions list must point to a node the
// iterator will be returning.
for (; index < node->child_count(); ++index)
if (prune.is_null() || !prune.Run(node->GetChild(index)))
break;
if (index < node->child_count())
positions_.push(Position<NodeType>(node, index));
}
explicit TreeNodeIterator(NodeType* node) {
if (!node->empty())
positions_.push(Position<NodeType>(node, 0));
}
// Returns true if there are more descendants.
bool has_next() const { return !positions_.empty(); }
// Returns the next descendant.
NodeType* Next() {
if (!has_next()) {
NOTREACHED();
return NULL;
}
// There must always be a valid node in the current Position index.
NodeType* result = positions_.top().node->GetChild(positions_.top().index);
// Make sure we don't attempt to visit result again.
positions_.top().index++;
// Iterate over result's children.
positions_.push(Position<NodeType>(result, 0));
// Advance to next valid node by skipping over the pruned nodes and the
// empty Positions. At the end of this loop two cases are possible:
// - the current index of the top() Position points to a valid node
// - the _position list is empty, the iterator has_next() will return false.
while (!positions_.empty()) {
if (positions_.top().index >= positions_.top().node->child_count())
positions_.pop(); // This Position is all processed, move to the next.
else if (!prune_.is_null() &&
prune_.Run(positions_.top().node->GetChild(positions_.top().index)))
positions_.top().index++; // Prune the branch.
else
break; // Now positioned at the next node to be returned.
}
return result;
}
private:
template <class PositionNodeType>
struct Position {
Position(PositionNodeType* node, int index) : node(node), index(index) {}
Position() : node(NULL), index(-1) {}
PositionNodeType* node;
int index;
};
std::stack<Position<NodeType> > positions_;
PruneCallback prune_;
DISALLOW_COPY_AND_ASSIGN(TreeNodeIterator);
};
} // namespace ui
#endif // UI_BASE_MODELS_TREE_NODE_ITERATOR_H_
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