QAbstractItemModel newbie question

[okellogg]

Many thanks for replying, wysota.

> your parent() implementation is invalid - you can't return an index by using
> ModelIndex:arent() because this method will call the model's parent() method
> to find the proper parent index

Okay. The problem then is, how do I get to the parent index when only given the
child index.
I resorted to a trick with internalPointer inEnumItemModel::index() :[*] on a top level item, call createIndex() with (void*)0 as the internalPointer[*] on a non toplevel item, call createIndex() with (parent.row() + 1) as the internalPointer

I would hope that there's a better way to get the parent index but I can't think of one...

> rowCount() will take an invalid model index for top level items, thus row() will
> return -1 and your rowCount() method will break

I'm not sure I understand that comment.
Here's my modified enumitemmodel.cpp:

#include <QtGui>
#include <iostream>
 
#include "enumitemmodel.h"
 
EnumItemModel::EnumItemModel(QObject *parent)
    : QAbstractItemModel(parent)
{
    setupModelData();
}
 
EnumItemModel::~EnumItemModel()
{
}
 
int EnumItemModel::columnCount(const QModelIndex &parent) const
{
    return 1;
}
 
QVariant EnumItemModel::data(const QModelIndex &index, int role) const
{
    if (!index.isValid())
        return QVariant();
 
    if (role != Qt::DisplayRole)
        return QVariant();
 
    const QModelIndex &parentIndex = index.parent();
 
    if (!parentIndex.isValid())
        return QVariant(enumTypes[index.row()].first);
 
    int parentRow = parentIndex.row();
    return QVariant(enumTypes[parentRow].second[index.row()]);
}
 
Qt::ItemFlags EnumItemModel::flags(const QModelIndex &index) const
{
    if (!index.isValid())
        return 0;
 
    return Qt::ItemIsEnabled | Qt::ItemIsSelectable;
}
 
QModelIndex EnumItemModel::index(int row, int column, const QModelIndex &parent)
            const
{
    if (!hasIndex(row, column, parent))
        return QModelIndex();
 
    if (!parent.isValid())
        return createIndex(row, column, NULL);
 
    long parentRowPlusOne = (long) parent.row() + 1;
    return createIndex(row, column, (void*)parentRowPlusOne);
}
 
QModelIndex EnumItemModel::parent(const QModelIndex &index) const
{
    if (!index.isValid())
        return QModelIndex();
 
    long parentRowPlusOne = (long)index.internalPointer();
    if (!parentRowPlusOne)  // Top level item
        return QModelIndex();
 
    return createIndex((int)parentRowPlusOne - 1, 0, NULL);
}
 
int EnumItemModel::rowCount(const QModelIndex &parent) const
{
    if (!parent.isValid())
        return 0;
 
    if (parent.column() > 0)
        return 0;
 
    //return enumTypes[parent.row()].second.count();   // or perhaps:
    long parentRowPlusOne = (long)parent.internalPointer();
    if (!parentRowPlusOne)
    {
        std::cerr << "EnumItemModel::rowCount(row=" << parent.row()
            << "): parentRowPlusOne is 0 ?!?" << std::endl;
        return 0;
    }
    return enumTypes[parentRowPlusOne - 1].second.count();
}
 
void EnumItemModel::setupModelData()
{
    QStringList booleanValues;
    booleanValues.append("False");
    booleanValues.append("True");
    enumTypes.append(EnumDefinition("Boolean", booleanValues));
 
    QStringList colorValues;
    colorValues.append("Red");
    colorValues.append("Green");
    colorValues.append("Blue");
    enumTypes.append(EnumDefinition("Color", colorValues));
}

#include <QtGui>
#include <iostream>

#include "enumitemmodel.h"

EnumItemModel::EnumItemModel(QObject *parent)
    : QAbstractItemModel(parent)
{
    setupModelData();
}

EnumItemModel::~EnumItemModel()
{
}

int EnumItemModel::columnCount(const QModelIndex &parent) const
{
    return 1;
}

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

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

    const QModelIndex &parentIndex = index.parent();

    if (!parentIndex.isValid())
        return QVariant(enumTypes[index.row()].first);

    int parentRow = parentIndex.row();
    return QVariant(enumTypes[parentRow].second[index.row()]);
}

Qt::ItemFlags EnumItemModel::flags(const QModelIndex &index) const
{
    if (!index.isValid())
        return 0;

    return Qt::ItemIsEnabled | Qt::ItemIsSelectable;
}

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

    if (!parent.isValid())
        return createIndex(row, column, NULL);

    long parentRowPlusOne = (long) parent.row() + 1;
    return createIndex(row, column, (void*)parentRowPlusOne);
}

QModelIndex EnumItemModel::parent(const QModelIndex &index) const
{
    if (!index.isValid())
        return QModelIndex();

    long parentRowPlusOne = (long)index.internalPointer();
    if (!parentRowPlusOne)  // Top level item
        return QModelIndex();

    return createIndex((int)parentRowPlusOne - 1, 0, NULL);
}

int EnumItemModel::rowCount(const QModelIndex &parent) const
{
    if (!parent.isValid())
        return 0;

    if (parent.column() > 0)
        return 0;

    //return enumTypes[parent.row()].second.count();   // or perhaps:
    long parentRowPlusOne = (long)parent.internalPointer();
    if (!parentRowPlusOne)
    {
        std::cerr << "EnumItemModel::rowCount(row=" << parent.row()
            << "): parentRowPlusOne is 0 ?!?" << std::endl;
        return 0;
    }
    return enumTypes[parentRowPlusOne - 1].second.count();
}

void EnumItemModel::setupModelData()
{
    QStringList booleanValues;
    booleanValues.append("False");
    booleanValues.append("True");
    enumTypes.append(EnumDefinition("Boolean", booleanValues));

    QStringList colorValues;
    colorValues.append("Red");
    colorValues.append("Green");
    colorValues.append("Blue");
    enumTypes.append(EnumDefinition("Color", colorValues));
}

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[jacek]

> rowCount() will take an invalid model index for top level items, thus row() will
> return -1 and your rowCount() method will break

I'm not sure I understand that comment.

"model.rowCount()" (or more precisely: "model.rowCount( QModelIndex() )" ) should return the number of top-level items and you have two such items ("Boolean" and "Color").

[okellogg]

"model.rowCount()" (or more precisely: "model.rowCount( QModelIndex() )" ) should return the number of top-level items and you have two such items ("Boolean" and "Color").

Yippie!

int EnumItemModel::rowCount(const QModelIndex &parent) const
{
    if (!parent.isValid())
        return enumTypes.count();
    [...]

int EnumItemModel::rowCount(const QModelIndex &parent) const
{
    if (!parent.isValid())
        return enumTypes.count();
    [...]

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With that change, I now got the top level items displayed:

- Boolean
- Color

And with the following, I got everything displayed:

int EnumItemModel::rowCount(const QModelIndex &parent) const
{
    if (parent.column() > 0)
        return 0;
    if (!parent.isValid())
        return enumTypes.count();
    return enumTypes[parent.row()].second.count();
}

int EnumItemModel::rowCount(const QModelIndex &parent) const
{
    if (parent.column() > 0)
        return 0;
    if (!parent.isValid())
        return enumTypes.count();
    return enumTypes[parent.row()].second.count();
}

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Last remaining problem: The leaf items ("False", "True", etc.) have a
"+" symbol and are expandable, and when expanding they show again
the same leaf items, again with "+" ad infinitum. (I'm sure that's an
easy one

Thanks again for your help, jacek and wysota.

[jacek]

Last remaining problem: The leaf items ("False", "True", etc.) have a
"+" symbol and are expandable, and when expanding they show again
the same leaf items, again with "+" ad infinitum. (I'm sure that's an
easy one

Try this: http://labs.trolltech.com/page/Proje...view/Modeltest.

[okellogg]

Just for completeness, the rowCount() was still faulty. Here's the corrected version:

int EnumItemModel::rowCount(const QModelIndex &parent) const
{
    if (parent.column() > 0)
        return 0;
    if (!parent.isValid())  // return total top level items
        return enumTypes.count();
    long parentRowPlusOne = (long)parent.internalPointer();
    if (!parentRowPlusOne)  // type name, e.g. "Color"
        return enumTypes[parent.row()].second.count();
    // leaf item, e.g. "Red"
    return 0;
}

int EnumItemModel::rowCount(const QModelIndex &parent) const
{
    if (parent.column() > 0)
        return 0;
    if (!parent.isValid())  // return total top level items
        return enumTypes.count();
    long parentRowPlusOne = (long)parent.internalPointer();
    if (!parentRowPlusOne)  // type name, e.g. "Color"
        return enumTypes[parent.row()].second.count();
    // leaf item, e.g. "Red"
    return 0;
}

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[wysota]

long parentRowPlusOne = (long)index.internalPointer();

long parentRowPlusOne = (long)index.internalPointer();

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How about QModelIndex::internalId() instead?

BTW. a trivial rowCount() implementation:

int Model::rowCount(const QModelIndex &parent) const {
  // if parent is invalid, return number of top level items
  if(!parent.isValid())
    return enumTypes.count();
  // if parent's parent is invalid, this is level one - return components' count
  if(!parent.parent().isValid() && hasIndex(parent))
    return enumTypes[parent.row()].second.count();
  // otherwise at least level 2 - none in our case
  return 0;
}

int Model::rowCount(const QModelIndex &parent) const {
  // if parent is invalid, return number of top level items
  if(!parent.isValid())
    return enumTypes.count();
  // if parent's parent is invalid, this is level one - return components' count
  if(!parent.parent().isValid() && hasIndex(parent))
    return enumTypes[parent.row()].second.count();
  // otherwise at least level 2 - none in our case
  return 0;
}

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No need for internal data and you can continue the descent ad infinitum depending on your needs. (for instance root -> QRect -> QPoint -> (int, int))

[rickbsgu]

How about QModelIndex::internalId() instead?

BTW. a trivial rowCount() implementation:

int Model::rowCount(const QModelIndex &parent) const {
  // if parent is invalid, return number of top level items
  if(!parent.isValid())
    return enumTypes.count();
  // if parent's parent is invalid, this is level one - return components' count
  if(!parent.parent().isValid() && hasIndex(parent))
    return enumTypes[parent.row()].second.count();
  // otherwise at least level 2 - none in our case
  return 0;
}

int Model::rowCount(const QModelIndex &parent) const {
  // if parent is invalid, return number of top level items
  if(!parent.isValid())
    return enumTypes.count();
  // if parent's parent is invalid, this is level one - return components' count
  if(!parent.parent().isValid() && hasIndex(parent))
    return enumTypes[parent.row()].second.count();
  // otherwise at least level 2 - none in our case
  return 0;
}

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No need for internal data and you can continue the descent ad infinitum depending on your needs. (for instance root -> QRect -> QPoint -> (int, int))

Following along, here - very interesting. Can you explain what the 'hasIndex' call does/verifies in this context?

thanx,
rickb

[wysota]

Whether parent.row() is within the valid range - [0 - rowCount(parent.parent())-1]. Instead you could use (enumTypes.count()>parent.row() && parent.row()>=0).

[ganeshshenoy]

Can you please post the updated code for this problem?