Reimpementing mapFromSource and mapToSource of QidentityProxyModel

[Guett_31]

Hello,

I'm trying to alter a QFileSystemModel by means of a subclassed QidentityProyModel. The alteration consists in removing all rows but one at a specific location in the proxy model, and I don't want any modifications in the source model.
I tried to reimplement the mapToSource and mapFromSource methods that way:

QModelIndex RootItemProxyModel::mapFromSource(const QModelIndex & sourceIdx) const
{
    // If the proxy is not activated, use the base mapFromSource function.
    if (m_ActivatedProxy == false)
        return IdentityFileSystemProxyModel::mapFromSource(sourceIdx);
 
    // Alter the mapping so the proxy model sees only m_rootSrcIdx's row as m_rootSrcParentIdx child.
    if (sourceIdx.parent().internalPointer() == m_rootSrcParentIdx.internalPointer())
    {
        if (sourceIdx.row() != 0)
            return QModelIndex();
        else
            return createIndex(0,
                               sourceIdx.column(),
                               sourceModel()->sibling(m_rootSrcIdx.row(),sourceIdx.column(),m_rootSrcIdx).internalPointer());
    }
    // In any other cases, use the base mapFromSource function.
    return IdentityFileSystemProxyModel::mapFromSource(sourceIdx);
}

QModelIndex RootItemProxyModel::mapFromSource(const QModelIndex & sourceIdx) const
{
    // If the proxy is not activated, use the base mapFromSource function.
    if (m_ActivatedProxy == false)
        return IdentityFileSystemProxyModel::mapFromSource(sourceIdx);

    // Alter the mapping so the proxy model sees only m_rootSrcIdx's row as m_rootSrcParentIdx child.
    if (sourceIdx.parent().internalPointer() == m_rootSrcParentIdx.internalPointer())
    {
        if (sourceIdx.row() != 0)
            return QModelIndex();
        else
            return createIndex(0,
                               sourceIdx.column(),
                               sourceModel()->sibling(m_rootSrcIdx.row(),sourceIdx.column(),m_rootSrcIdx).internalPointer());
    }
    // In any other cases, use the base mapFromSource function.
    return IdentityFileSystemProxyModel::mapFromSource(sourceIdx);
}

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QModelIndex RootItemProxyModel::mapToSource(const QModelIndex & proxyIndex) const
{
    // If the proxy is not activated, use the base mapToSource function.
    if (m_ActivatedProxy == false)
        return IdentityFileSystemProxyModel::mapToSource(proxyIndex);
 
    // Alter the mapping so the proxy model sees only m_rootSrcIdx's row as m_rootSrcParentIdx child.
    QModelIndex sourceIdx = IdentityFileSystemProxyModel::mapToSource(proxyIndex);
    if (sourceIdx.parent().internalPointer() == m_rootSrcParentIdx.internalPointer())
    {
        if (proxyIndex.row() != 0)
            return QModelIndex();
        else
            return sourceModel()->sibling(m_rootSrcIdx.row(),
                                          proxyIndex.column(),
                                          m_rootSrcIdx);
    }
    // In any other cases, use the base mapToSource function.
    return sourceIdx;
}

QModelIndex RootItemProxyModel::mapToSource(const QModelIndex & proxyIndex) const
{
    // If the proxy is not activated, use the base mapToSource function.
    if (m_ActivatedProxy == false)
        return IdentityFileSystemProxyModel::mapToSource(proxyIndex);

    // Alter the mapping so the proxy model sees only m_rootSrcIdx's row as m_rootSrcParentIdx child.
    QModelIndex sourceIdx = IdentityFileSystemProxyModel::mapToSource(proxyIndex);
    if (sourceIdx.parent().internalPointer() == m_rootSrcParentIdx.internalPointer())
    {
        if (proxyIndex.row() != 0)
            return QModelIndex();
        else
            return sourceModel()->sibling(m_rootSrcIdx.row(),
                                          proxyIndex.column(),
                                          m_rootSrcIdx);
    }
    // In any other cases, use the base mapToSource function.
    return sourceIdx;
}

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The only examples I could find about mapToSource and mapFromSource reimplemented methods were for transpose proxy models in which each Modelindex in the Source model maps to a Modelindex in the Proxy model. In my case, the Proxy model has less Modelindexes than the SourceModel. I return QModelIndex() for any ModelIndex that maps to, or from, a ModelIndex that belong to the rows I want to remove.
I'm not sure that it is what I should return in that case. I'm not even sure that my overall strategy is correct.

If someone experienced can put me on the right track, that would be great.
Thanks.

[anda_skoa]

Let me try to understand this: you want the proxy model to filter out rows, yet you are using the QIdentityProxyModel as a base class, which works with the base assumption that it does not change the data's structure.
Hence it being called QIdentityProxyModel.

Wouldn't it be much easier to base this on QSortFilterProxyModel and implement filterAcceptsRow()?

Cheers,
_

[Guett_31]

Ideally I would use a QSortFilterProxyModel as you suggested. My problem is that other QIdentityProxyModels would be chained to that QSortFilterProxyModel for subsequent data processing in my project. According to my limited Qt experience, QSortFilterProxyModels and QIdentityProxyModels don't go well together. I reported a bug about that 9 month ago and it has not even been evaluated yet: QTBUG-32981
[URL="https://bugreports.qt-project.org/browse/QTBUG-32981"]
I tried to work around that by using a QIdentityProxyModel instead, so I have only QIdentityProxyModels in my proxy model chain.

[anda_skoa]

Well, my guess would be that time would best be spent on fixing the bug, but if you really need your own filter model it is probably better to base it off QAbstractProxyModel instead of making QIdentityProxyModel do the opposite of that it is intended for.

Cheers,
_