QTreeView display of graph (multiple parents of item)

[Petro Svintsitskyi]

I know this thread is too old, but maybe my findings will be useful.

I also wanted to have multiple parents for my qtreeview entities (items) and came up with the following solution.

I have an IndexData structure that contains information about current item and it's parent:

struct IndexData{
        IndexData *parentIndex;
        Entity *parent;
        Entity *item;
        int row;
};

struct IndexData{
        IndexData *parentIndex;
        Entity *parent;
        Entity *item;
        int row;
};

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When QAbstractItemModel::createIndex() function is called, I pass a pointer to IndexData structure as the third parameter.

Full item model class is the following (Please note that it is a quick and dirty solution with memory leaks that was not well tested):

#include "entitymodel.h"
#include <QDebug>
 
EntityModel::EntityModel(Entity *root, QObject *parent) :
    QAbstractItemModel(parent)
{
    m_root = root;
    m_rootIndexData = new IndexData;
    m_rootIndexData->parent = 0;
    m_rootIndexData->parentIndex = 0;
    m_rootIndexData->row = 0;
    m_rootIndexData->item = root;
}
 
QModelIndex EntityModel::index(int row, int column, const QModelIndex &parent) const
{
    if (!hasIndex(row, column, parent)) {
        return QModelIndex();
    }
 
    IndexData *parentData = indexData(parent);
    Entity *child = parentData->item->child(row);
 
    if (child)
        return createIndex(row, column, createIndexData(parentData, child, row));
 
    return QModelIndex();
}
 
QModelIndex EntityModel::parent(const QModelIndex &child) const
{
    if (!child.isValid())
        return QModelIndex();
 
    IndexData *data = indexData(child);
    if (data->parent == m_root) {
        return QModelIndex();
    }
 
    if (data->parentIndex == 0)
        return QModelIndex();
 
    return createIndex(data->parentIndex->row, 0, data->parentIndex);
}
 
int EntityModel::rowCount(const QModelIndex &parent) const
{
    IndexData *data = indexData(parent);
    return data->item->childrenCount();
}
 
int EntityModel::columnCount(const QModelIndex &parent) const
{
    return 2;
}
 
QVariant EntityModel::data(const QModelIndex &index, int role) const
{
    if (!index.isValid())
        return QVariant();
 
    if (role != Qt::DisplayRole)
        return QVariant();
 
    Entity *item = indexData(index)->item;
 
    if (index.column() == 0) {
        return item->name();
    } else if (index.column() == 1) {
        return "Entity";
    } else {
        qCritical() << "Invalid column";
        return "";
    }
}
 
EntityModel::IndexData *EntityModel::indexData(const QModelIndex &index) const
{
    if (index.isValid()) {
        IndexData *data = static_cast<IndexData*>(index.internalPointer());
        if (data)
            return data;
    }
 
    return m_rootIndexData;
}
 
EntityModel::IndexData *EntityModel::createIndexData(IndexData *parent, Entity *item, int row) const
{
    if (!m_indexData.contains(quintptr(parent->item))) {
        QHash<quintptr, IndexData*>* hash = new QHash<quintptr, IndexData*>();
        m_indexData.insert(quintptr(parent->item), hash);
    }
 
    if (!m_indexData[quintptr(parent->item)]->contains(quintptr(item))) {
        IndexData *data = new IndexData;
        data->parent = parent->item;
        data->item = item;
        data->parentIndex = parent;
        data->row = row;
        m_indexData[quintptr(parent->item)]->insert(quintptr(item), data);
    }
 
    return m_indexData[quintptr(parent->item)]->value(quintptr(item));
}

#include "entitymodel.h"
#include <QDebug>

EntityModel::EntityModel(Entity *root, QObject *parent) :
    QAbstractItemModel(parent)
{
    m_root = root;
    m_rootIndexData = new IndexData;
    m_rootIndexData->parent = 0;
    m_rootIndexData->parentIndex = 0;
    m_rootIndexData->row = 0;
    m_rootIndexData->item = root;
}

QModelIndex EntityModel::index(int row, int column, const QModelIndex &parent) const
{
    if (!hasIndex(row, column, parent)) {
        return QModelIndex();
    }

    IndexData *parentData = indexData(parent);
    Entity *child = parentData->item->child(row);

    if (child)
        return createIndex(row, column, createIndexData(parentData, child, row));

    return QModelIndex();
}

QModelIndex EntityModel::parent(const QModelIndex &child) const
{
    if (!child.isValid())
        return QModelIndex();

    IndexData *data = indexData(child);
    if (data->parent == m_root) {
        return QModelIndex();
    }

    if (data->parentIndex == 0)
        return QModelIndex();

    return createIndex(data->parentIndex->row, 0, data->parentIndex);
}

int EntityModel::rowCount(const QModelIndex &parent) const
{
    IndexData *data = indexData(parent);
    return data->item->childrenCount();
}

int EntityModel::columnCount(const QModelIndex &parent) const
{
    return 2;
}

QVariant EntityModel::data(const QModelIndex &index, int role) const
{
    if (!index.isValid())
        return QVariant();

    if (role != Qt::DisplayRole)
        return QVariant();

    Entity *item = indexData(index)->item;

    if (index.column() == 0) {
        return item->name();
    } else if (index.column() == 1) {
        return "Entity";
    } else {
        qCritical() << "Invalid column";
        return "";
    }
}

EntityModel::IndexData *EntityModel::indexData(const QModelIndex &index) const
{
    if (index.isValid()) {
        IndexData *data = static_cast<IndexData*>(index.internalPointer());
        if (data)
            return data;
    }

    return m_rootIndexData;
}

EntityModel::IndexData *EntityModel::createIndexData(IndexData *parent, Entity *item, int row) const
{
    if (!m_indexData.contains(quintptr(parent->item))) {
        QHash<quintptr, IndexData*>* hash = new QHash<quintptr, IndexData*>();
        m_indexData.insert(quintptr(parent->item), hash);
    }

    if (!m_indexData[quintptr(parent->item)]->contains(quintptr(item))) {
        IndexData *data = new IndexData;
        data->parent = parent->item;
        data->item = item;
        data->parentIndex = parent;
        data->row = row;
        m_indexData[quintptr(parent->item)]->insert(quintptr(item), data);
    }

    return m_indexData[quintptr(parent->item)]->value(quintptr(item));
}

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[d_stranz]

Thanks for this. Now I need to figure out how to implement a model that will handle an undirected cyclic graph which may contain disjoint subgraphs :-) I might have to save that for another lifetime.