QTreeView display of graph (multiple parents of item)

[wysota]

Usually one implements the following structure:

struct Item {
    Item *parent;
    QList<Item*> children;
};

struct Item {
    Item *parent;
    QList<Item*> children;
};

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and then parent() becomes something like:

QModelIndex Model::parent(const QModelIndex &index) const {
  if(!index.isValid()) return QModelIndex();
  Item *item = static_cast<Item*>(index.internalPointer());
  Item *parent = item->parent;
  if(parent == m_rootItem ) { return QModelIndex(); } // I'm top level
  Item *grandParent = parent->parent;
  int row = grandParent->children.indexOf(parent); // find out the row number of the parent
  return createIndex(row, 0, parent);
};

QModelIndex Model::parent(const QModelIndex &index) const {
  if(!index.isValid()) return QModelIndex();
  Item *item = static_cast<Item*>(index.internalPointer());
  Item *parent = item->parent;
  if(parent == m_rootItem ) { return QModelIndex(); } // I'm top level
  Item *grandParent = parent->parent;
  int row = grandParent->children.indexOf(parent); // find out the row number of the parent
  return createIndex(row, 0, parent);
};

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This makes sense for trees while it doesn't have to make sense for arbitrary graphs (there is no concept of a root item). And I understood the OP's question correctly and I gave a good answer (to make the tree model a subset of an external graph representation) for it.